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• How can I structure and recode messy categorical data in R?

  - by briandk

  I'm struggling with how to best structure categorical data that's messy, and comes from a dataset I'll need to clean. The Coding Scheme I'm analyzing data from a university science course exam. We're looking at patterns in student responses, and we developed a coding scheme to represent the kinds of things students are doing in their answers. A subset of the coding scheme is shown below. Note that within each major code (1, 2, 3) are nested non-unique sub-codes (a, b, ...). What the Raw Data Looks Like I've created an anonymized, raw subset of my actual data which you can view here. Part of my problem is that those who coded the data noticed that some students displayed multiple patterns. The coders' solution was to create enough columns (reason1, reason2, ...) to hold students with multiple patterns. That becomes important because the order (reason1, reason2) is arbitrary--two students (like student 41 and student 42 in my dataset) who correctly applied "dependency" should both register in an analysis, regardless of whether 3a appears in the reason column or the reason2 column. How Can I Best Structure Student Data? Part of my problem is that in the raw data, not all students display the same patterns, or the same number of them, in the same order. Some students may do just one thing, others may do several. So, an abstracted representation of example students might look like this: Note in the example above that student002 and student003 both are coded as "1b", although I've deliberately shown the order as different to reflect the reality of my data. My (Practical) Questions Should I concatenate reason1, reason2, ... into one column? How can I (re)code the reasons in R to reflect the multiplicity for some students? Thanks I realize this question is as much about good data conceptualization as it is about specific features of R, but I thought it would be appropriate to ask it here. If you feel it's inappropriate for me to ask the question, please let me know in the comments, and stackoverflow will automatically flood my inbox with sadface emoticons. If I haven't been specific enough, please let me know and I'll do my best to be clearer.

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• How to initiate chatting between two clients and two clients only, using applets and servlets?

  - by mithun1538

  Hello everyone, I first need to apologize for my earlier questions. (You can check my profile for them)They seemed to ask more questions than give answers. Hence, I am laying down the actual question that started all them absurd questions. I am trying to design a chat applet. Till now, I have coded the applet, servlet and communication between the applet and the servlet. The code in the servlet side is such that I was able to establish chatting between clients using the applets, but the code was more like a broadcast all feature, i.e. all clients would be chatting with each other. That was my first objective when I started designing the chat applet. The second step is chatting between only two specific users, much like any other chat application we have. So this was my idea for it: I create an instance of the servlet that has the 'broadcast-all' code. I then pass the address of this instance to the respective clients. 2 client applets use the address to then chat. Technically the code is 'broadcast-all', but since only 2 clients are connected to it, it gives the chatting between two clients feature. Thus, groups of 2 clients have different instances of the same servlet, and each instance handles chatting between two clients at a max. However, as predicted, the idea didn't materialize! I tried to create an instance of the servlet but the only solution for that was using sessions on the servlet side, and I don't know how to use this session for later communications. I then tried to modify my broadcast-all code. In that code, I was using classes that implemented Observer and Observable interfaces. So the next idea that I got was: Create a new object of the Observable class(say class_1). This object be common to 2 clients. 2 clients that wish to chat will use same object of the class_1. 2 other clients will use a different object of class_1. But the problem here lies with the class that implements the Observer interface(say class_2). Since this has observers monitoring the same type of class, namely class_1, how do I establish an observer monitoring one object of class_1 and another observer monitoring another object of the same class class_1 (Because notifyObservers() would notify all the observers and I can't assign a particular observer to a particular object)? I first decided to ask individual problems, like how to create instances of servlets, using objects of observable and observer and so on in stackoverflow... but I got confused even more. Can anyone give me an idea how to establish chatting between two clients only?(I am using Http and not sockets or RMI). Regards, Mithun. P.S. Thanks to all who replied to my previous (absurd) queries. I should have stated the purpose earlier so that you guys could help me better.

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• Autocomplete server-side implementation

  - by toluju

  What is a fast and efficient way to implement the server-side component for an autocomplete feature in an html input box? I am writing a service to autocomplete user queries in our web interface's main search box, and the completions are displayed in an ajax-powered dropdown. The data we are running queries against is simply a large table of concepts our system knows about, which matches roughly with the set of wikipedia page titles. For this service obviously speed is of utmost importance, as responsiveness of the web page is important to the user experience. The current implementation simply loads all concepts into memory in a sorted set, and performs a simple log(n) lookup on a user keystroke. The tailset is then used to provide additional matches beyond the closest match. The problem with this solution is that it does not scale. It currently is running up against the VM heap space limit (I've set -Xmx2g, which is about the most we can push on our 32 bit machines), and this prevents us from expanding our concept table or adding more functionality. Switching to 64-bit VMs on machines with more memory isn't an immediate option. I've been hesitant to start working on a disk-based solution as I am concerned that disk seek time will kill performance. Are there possible solutions that will let me scale better, either entirely in memory or with some fast disk-backed implementations? Edits: @Gandalf: For our use case it is important the the autocompletion is comprehensive and isn't just extra help for the user. As for what we are completing, it is a list of concept-type pairs. For example, possible entries are [("Microsoft", "Software Company"), ("Jeff Atwood", "Programmer"), ("StackOverflow.com", "Website")]. We are using Lucene for the full search once a user selects an item from the autocomplete list, but I am not yet sure Lucene would work well for the autocomplete itself. @Glen: No databases are being used here. When I'm talking about a table I just mean the structured representation of my data. @Jason Day: My original implementation to this problem was to use a Trie, but the memory bloat with that was actually worse than the sorted set due to needing a large number of object references. I'll read on the ternary search trees to see if it could be of use.

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• How come my South migrations doesn't work for Django?

  - by TIMEX

  First, I create my database. create database mydb; I add "south" to installed Apps. Then, I go to this tutorial: http://south.aeracode.org/docs/tutorial/part1.html The tutorial tells me to do this: $ py manage.py schemamigration wall --initial >>> Created 0001_initial.py. You can now apply this migration with: ./manage.py migrate wall Great, now I migrate. $ py manage.py migrate wall But it gives me this error... django.db.utils.DatabaseError: (1146, "Table 'fable.south_migrationhistory' doesn't exist") So I use Google (which never works. hence my 870 questions asked on Stackoverflow), and I get this page: http://groups.google.com/group/south-users/browse_thread/thread/d4c83f821dd2ca1c Alright, so I follow that instructions >> Drop database mydb; >> Create database mydb; $ rm -rf ./wall/migrations $ py manage.py syncdb But when I run syncdb, Django creates a bunch of tables. Yes, it creates the south_migrationhistory table, but it also creates my app's tables. Synced: > django.contrib.admin > django.contrib.auth > django.contrib.contenttypes > django.contrib.sessions > django.contrib.sites > django.contrib.messages > south > fable.notification > pagination > timezones > fable.wall > mediasync > staticfiles > debug_toolbar Not synced (use migrations): - (use ./manage.py migrate to migrate these) Cool....now it tells me to migrate these. So, I do this: $ py manage.py migrate wall The app 'wall' does not appear to use migrations. Alright, so fine. I'll add wall to initial migrations. $ py manage.py schemamigration wall --initial Then I migrate: $ py manage.py migrate wall You know what? It gives me this BS: _mysql_exceptions.OperationalError: (1050, "Table 'wall_content' already exists") Sorry, this is really pissing me off. Can someone help ? thanks. How do I get South to work and sync correctly with everything?

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• Idiomatic use of auto_ptr to transfer ownership to a container

  - by heycam

  I'm refreshing my C++ knowledge after not having used it in anger for a number of years. In writing some code to implement some data structure for practice, I wanted to make sure that my code was exception safe. So I've tried to use std::auto_ptrs in what I think is an appropriate way. Simplifying somewhat, this is what I have: class Tree { public: ~Tree() { /* delete all Node*s in the tree */ } void insert(const string& to_insert); ... private: struct Node { ... vector<Node*> m_children; }; Node* m_root; }; template<T> void push_back(vector<T*>& v, auto_ptr<T> x) { v.push_back(x.get()); x.release(); } void Tree::insert(const string& to_insert) { Node* n = ...; // find where to insert the new node ... push_back(n->m_children, auto_ptr<Node>(new Node(to_insert)); ... } So I'm wrapping the function that would put the pointer into the container, vector::push_back, and relying on the by-value auto_ptr argument to ensure that the Node* is deleted if the vector resize fails. Is this an idiomatic use of auto_ptr to save a bit of boilerplate in my Tree::insert? Any improvements you can suggest? Otherwise I'd have to have something like: Node* n = ...; // find where to insert the new node auto_ptr<Node> new_node(new Node(to_insert)); n->m_children.push_back(new_node.get()); new_node.release(); which kind of clutters up what would have been a single line of code if I wasn't worrying about exception safety and a memory leak. (Actually I was wondering if I could post my whole code sample (about 300 lines) and ask people to critique it for idiomatic C++ usage in general, but I'm not sure whether that kind of question is appropriate on stackoverflow.)

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• How do I stack images to simulate depth using Core Animation?

  - by Jeffrey Berthiaume

  I have a series of UIImages with which I need to simulate depth. I can't use scaling because I need to be able to rotate the parent view, and the images should look like they're stacked visibly in front of each other, not on the same plane. I made a new ViewController-based project and put this in the viewDidLoad (as well as attached three 120x120 pixel images named 1.png, 2.png, and 3.png): - (void)viewDidLoad { // display image 3 UIImageView *three = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"3.png"]]; three.center = CGPointMake(160 + 60, 240 - 60); [self.view addSubview:three]; // rotate image 3 around the z axis // THIS IS INCORRECT CATransform3D theTransform = three.layer.transform; theTransform.m34 = 1.0 / -1000; three.layer.transform = theTransform; // display image 2 UIImageView *two = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"2.png"]]; two.center = CGPointMake(160, 240); [self.view addSubview:two]; // display image 1 UIImageView *one = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"1.png"]]; one.center = CGPointMake(160 - 60, 240 + 60); [self.view addSubview:one]; // rotate image 3 around the z axis // THIS IS INCORRECT theTransform = one.layer.transform; theTransform.m34 = 1.0 / 1000; one.layer.transform = theTransform; // release the images [one release]; [two release]; [three release]; // rotate the parent view around the y axis theTransform = self.view.layer.transform; theTransform.m14 = 1.0 / -500; self.view.layer.transform = theTransform; [super viewDidLoad]; } I have very specific reasons why I'm not using an EAGLView and why I'm not loading the images as CALayers (i.e. why I'm using UIImageViews for each one). This is just a quick demo that I can use to work out exactly what I need in my parent application. Is there some matrix way to translate these 2d images along the z-axis so they will look like what I'm trying to represent? I've gone through the other StackOverflow articles as well as the Wikipedia references, and have not found what I'm looking for -- although I might not necessarily be using the right terms for what I'm trying to do.

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• HTML: order of divs and a tags for href

  - by user2962389

  I'm busy with HTML and CSS and got stuck with this. I have created a button with :hover and :active options, which is centered on the page. Clicking on this button needs to lead to a website. My HTML is: <div> <a href="website"><div id="button">Text</div></a> </div> The CSS is: body, html { height: 100%; } a { text-decoration: none; } #button { text-transform: uppercase; font-size: 18px; text-align: center; padding: 1em 0.5em 0.8em; background-color: white; font-family: Myriad Pro, Source Sans Pro, Helvetica, Arial, sans-serif; color: #ff4700; cursor: pointer; width: 150px; -webkit-border-radius: 5px; -moz-border-radius: 5px; border-radius: 5px; border: 1px solid #ff4700; margin-left: auto; margin-right: auto; margin-bottom: 50px; -webkit-transition: all .1s ease; -moz-transition: all .1s ease; -ms-transition: all .1s ease; -o-transition: all .1s ease; transition: all .1s ease; } #button:hover { background-color: #ff4700; color: white; border: 1px solid white; } #button:active { background-color: #cc3900; } The problem lies in the fact that the whole width of the page is clickable at the height of the button and not only the button itself that is 150px wide and is centered on the page. I think I have my divs mixed up and it needs other formatting and precedence, but I'm not sure. Thanks for your help! P.S. First time on StackOverflow, sorry if I formatted something wrong.

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• UITableViewCell outlets not set during bundle load (possibly very elementary question)

  - by Jan Zich

  What are the most common reasons for an outlet (a class property) not being set during a bundle load? I'm sorry; most likely I'm not using the correct terms. It's my first steps with iPhone OS development and Objective-C, so please bear with me. Here is more details. Basically, I'm trying to create a table view based form with a fixed number of static rows. I followed this example: http://developer.apple.com/iphone/library/documentation/userexperience/conceptual/TableView_iPhone/TableViewCells/TableViewCells.html Scroll down to The Technique for Static Row Content please. I have one nib file with one table view, three table cells and all connections set as in the example. The problem is that the corresponding cell properties in my controller are never initialised. I get an exception in cellForRowAtIndexPath complaining that the returned cell is nil: UITableView dataSource must return a cell from tableView:cellForRowAtIndexPath. Here are the relevant parts from the implementation of the controller: @synthesize cellA; @synthesize cellB; @synthesize cellC; - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return 1; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return 3; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { switch (indexPath.row) { case 0: return cellA; break; case 1: return cellB; break; case 2: return cellC; break; default: return nil; } } And here is the interface part: @interface AssociatePhoneViewController : UITableViewController { UITableViewCell *cellA; UITableViewCell *cellB; UITableViewCell *cellB; } @property (nonatomic, retain) IBOutlet UITableViewCell *cellA; @property (nonatomic, retain) IBOutlet UITableViewCell *cellB; @property (nonatomic, retain) IBOutlet UITableViewCell *cellC; @end This must be possibly one of the the most embarrassing questions on StackOverflow. It looks like the most basic example code. Is is possible that the cells are not instantiated with the nib file? I have them on the same level before the tabula view in the nib file. I tried to move them after the table view, but it did not make any difference. Are table cells in some way special? Do I need to set some flag or some property on them in the nib file? I was under the impression that all classes (views, windows, controllers …) listed in a nib file are simply instantiated (and linked using the provided connections). Could it possibly be some memory issue? The cell properties in my controller are not defined in any special way.

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• impress.js Navigation with active class

  - by ArtGoddess

  I would like to use impress.js in order to make a website, with a navigation bar. In each slide, the corresponding anchor or div must have an "active" class, in order to achieve a different link appearance. I have followed all instructions provided here: https://github.com/Ralt/impress.js/commit/f88feb8cae704ce27bd2168bdb77768f516ac2da#L2R605 but the "active" class on the correct menu must be added. This is the code that generates the menu items. How can I add for example the "active" class in the first link? /* ************************ MENU ***************************** */ // Capitalize first letter of string // @see http://stackoverflow.com/a/1026087/851498 var capitalize = function( str ) { return str.charAt(0).toUpperCase() + str.slice(1); } // `showMenu` API function creates the menu // It defines the names of each entry by the id capitalized. var showMenu = function() { // Create the menu wrapper and the element that will be cloned // for each entry. var menu = document.createElement('div'), el = document.createElement('div'); // Apply some classes menu.className = 'menu'; el.className = 'menu-item'; // Create an element that will be the "button" and append it // to the menu var button = document.createElement('div'); button.className = 'menu-button'; button.textContent = 'Menu'; menu.appendChild(button); // Now, for each div in #impress, add an entry to the menu [].forEach.call(byId('impress').firstElementChild.children, function( child, index ) { var newEl = el.cloneNode(), i = index + 1, text = i + '. ' + capitalize(child.id); // Set the text of the new element newEl.textContent = text; // Add an onclick event to the new element // We need to use a closure to make sure the index is correct (function( index ) { newEl.addEventListener('click', function() { goto(index); }); }( index )); // And append the new element to the menu menu.appendChild(newEl); }); // And append the menu to #impress document.body.appendChild(menu); }; Then, in each click it must be removed the active class on the current, and add it to the clicked element. // Remove the active class from the current active document.querySelector( '.active' )[ 0 ].classList.remove( 'active' ); // And add it to the clicked index byId('impress').firstElementChild.children[ index ].classList.add( 'active' ); Where do I have to apply this code? Thank you!

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• Setting up Netbeans/Eclipse for Linux Kernel Development

  - by red.october

  Hi: I'm doing some Linux kernel development, and I'm trying to use Netbeans. Despite declared support for Make-based C projects, I cannot create a fully functional Netbeans project. This is despite compiling having Netbeans analyze a kernel binary that was compiled with full debugging information. Problems include: files are wrongly excluded: Some files are incorrectly greyed out in the project, which means Netbeans does not believe they should be included in the project, when in fact they are compiled into the kernel. The main problem is that Netbeans will miss any definitions that exist in these files, such as data structures and functions, but also miss macro definitions. cannot find definitions: Pretty self-explanatory - often times, Netbeans cannot find the definition of something. This is partly a result of the above problem. can't find header files: self-explanatory I'm wondering if anyone has had success with setting up Netbeans for Linux kernel development, and if so, what settings they used. Ultimately, I'm looking for Netbeans to be able to either parse the Makefile (preferred) or extract the debug information from the binary (less desirable, since this can significantly slow down compilation), and automatically determine which files are actually compiled and which macros are actually defined. Then, based on this, I would like to be able to find the definitions of any data structure, variable, function, etc. and have complete auto-completion. Let me preface this question with some points: I'm not interested in solutions involving Vim/Emacs. I know some people like them, but I'm not one of them. As the title suggest, I would be also happy to know how to set-up Eclipse to do what I need While I would prefer perfect coverage, something that only misses one in a million definitions is obviously fine SO's useful "Related Questions" feature has informed me that the following question is related: http://stackoverflow.com/questions/149321/what-ide-would-be-good-for-linux-kernel-driver-development. Upon reading it, the question is more of a comparison between IDE's, whereas I'm looking for how to set-up a particular IDE. Even so, the user Wade Mealing seems to have some expertise in working with Eclipse on this kind of development, so I would certainly appreciate his (and of course all of your) answers. Cheers

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• Python/Biomolecular Physics- Trying to code a simple stochastic simulation of a system exhibiting co

  - by user359597

  *edited 6/17/10 I'm trying to understand how to improve my code (make it more pythonic). Also, I'm interested in writing more intuitive 'conditionals' that would describe scenarios that are commonplace in biochemistry. The conditional criteria in the below program is explained in Answer #2, but I am not satisfied with it- it is correct, but isn't obvious and isn't easy to implement for more complicated conditional scenarios. Ideas welcome. Comments/criticisms welcome. First posting experience @ stackoverflow- please comment on etiquette if needed. The code generates a list of values that are the solution to the following exercise: "In a programming language of your choice, implement Gillespie’s First Reaction Algorithm to study the temporal behaviour of the reaction A---B in which the transition from A to B can only take place if another compound, C, is present, and where C dynamically interconverts with D, as modelled in the Petri-net below. Assume that there are 100 molecules of A, 1 of C, and no B or D present at the start of the reaction. Set kAB to 0.1 s-1 and both kCD and kDC to 1.0 s-1. Simulate the behaviour of the system over 100 s." def sim(): # Set the rate constants for all transitions kAB = 0.1 kCD = 1.0 kDC = 1.0 # Set up the initial state A = 100 B = 0 C = 1 D = 0 # Set the start and end times t = 0.0 tEnd = 100.0 print "Time\t", "Transition\t", "A\t", "B\t", "C\t", "D" # Compute the first interval transition, interval = transitionData(A, B, C, D, kAB, kCD, kDC) # Loop until the end time is exceded or no transition can fire any more while t <= tEnd and transition >= 0: print t, '\t', transition, '\t', A, '\t', B, '\t', C, '\t', D t += interval if transition == 0: A -= 1 B += 1 if transition == 1: C -= 1 D += 1 if transition == 2: C += 1 D -= 1 transition, interval = transitionData(A, B, C, D, kAB, kCD, kDC) def transitionData(A, B, C, D, kAB, kCD, kDC): """ Returns nTransition, the number of the firing transition (0: A->B, 1: C->D, 2: D->C), and interval, the interval between the time of the previous transition and that of the current one. """ RAB = kAB * A * C RCD = kCD * C RDC = kDC * D dt = [-1.0, -1.0, -1.0] if RAB > 0.0: dt[0] = -math.log(1.0 - random.random())/RAB if RCD > 0.0: dt[1] = -math.log(1.0 - random.random())/RCD if RDC > 0.0: dt[2] = -math.log(1.0 - random.random())/RDC interval = 1e36 transition = -1 for n in range(len(dt)): if dt[n] > 0.0 and dt[n] < interval: interval = dt[n] transition = n return transition, interval if __name__ == '__main__': sim()

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• Publish to Facebook Stream via PHP using Graph API

  - by Liquid

  I'm trying to post a message to a user's wall using the new graph API and PHP. Connection seems to work fine, but no post appears. I'm not sure how to set up the posting code correctly. Please help me out. Sorry for the broken-looking code, for some reason StackOverflow didn't want to close it all in the code block. Below is my full code. Am I missing an extender permission requests, or is that taken care in this code: PHP Code <?php include_once 'facebook.php'; $facebook = new Facebook(array( 'appId' => 'xxxxxxxxxxxxxxxxxx', 'secret' => 'xxxxxxxxxxxxxxxxxxxxxxxxxx', 'cookie' => true )); $session = $facebook->getSession(); if (!$session) { $url = $facebook->getLoginUrl(array( 'canvas' => 1, 'fbconnect' => 0 )); echo "<script type='text/javascript'>top.location.href = '$url';</script>"; } else { try { $uid = $facebook->getUser(); $me = $facebook->api('/me'); $updated = date("l, F j, Y", strtotime($me['updated_time'])); echo "Hello " . $me['name'] . "<br />"; echo "You last updated your profile on " . $updated; $connectUrl = $facebook->getUrl( 'www', 'login.php', array_merge(array( 'api_key' => $facebook->getAppId(), 'cancel_url' => 'http://www.test.com', 'req_perms' => 'publish_stream', 'display' => 'page', 'fbconnect' => 1, 'next' => 'http://www.test.com', 'return_session' => 1, 'session_version' => 3, 'v' => '1.0', ), $params) ); $result = $facebook->api( '/me/feed/', 'post', array('access_token' => $facebook->access_token, 'message' => 'Playing around with FB Graph..') ); } catch (FacebookApiException $e) { echo "Error:" . print_r($e, true); } } ?>

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• DataContractSerializer and XSLT

  - by Russ Clark

  I've got a simple Employee class that I'm trying to serialize to an XDocument and then use XSLT to transform the document to a page that displays both the properties (Name and ID) from the Employee class, and an html form with 2 radio buttons (Approve and Reject) and a submit button. Here is the Employee class: [Serializable, DataContract(Namespace="XSLT_MVC.Controllers/")] public class Employee { [DataMember] public string Name { get; set; } [DataMember] public int ID { get; set; } public Employee() { } public Employee(string name, int id) { Name = name; ID = id; } public XDocument GetDoc() { XDocument doc = new XDocument(); var serializer = new DataContractSerializer(typeof(Employee)); using (var writer = doc.CreateWriter()) { serializer.WriteObject(writer, this); writer.Close(); } return doc; } } And here is the XSLT file: <?xml version="1.0" encoding="utf-8"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" > <xsl:output method="html" indent="yes"/> <xsl:template match="/"> <html> <body> <xsl:value-of select="Employee/Name"/> <br /> <xsl:value-of select="Employee/ID"/> <br /> <form method="post" action="/Home/ProcessRequest?id={Employee/ID}"> <input id="Action" name="Action" type="radio" value="Approved"></input> Approved <br /> <input id="Action" name="Action" type="radio" value="Rejected"></input> Rejected <br /> <input type="submit" value="Submit"></input> </form> </body> </html> </xsl:template> </xsl:stylesheet> When I run this, all I get is the html form with the 2 radio buttons and the submit button, but not the properties from the Employee class. I saw a separate StackOverflow post that said I need to change the <xsl:template match="/"> to match on the namespace of my Employee class like this: <xsl:template match="/XSLT_MVC.Controllers">, but when I do that, now all I get are the Employee properties, and not the html form with the 2 radio buttons and the submit button. Does anyone know what needs to be done so that my transform will select and display both the Employee properties and the html form?

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• Supporting multiple instances of a plugin DLL with global data

  - by Bruno De Fraine

  Context: I converted a legacy standalone engine into a plugin component for a composition tool. Technically, this means that I compiled the engine code base to a C DLL which I invoke from a .NET wrapper using P/Invoke; the wrapper implements an interface defined by the composition tool. This works quite well, but now I receive the request to load multiple instances of the engine, for different projects. Since the engine keeps the project data in a set of global variables, and since the DLL with the engine code base is loaded only once, loading multiple projects means that the project data is overwritten. I can see a number of solutions, but they all have some disadvantages: You can create multiple DLLs with the same code, which are seen as different DLLs by Windows, so their code is not shared. Probably this already works if you have multiple copies of the engine DLL with different names. However, the engine is invoked from the wrapper using DllImport attributes and I think the name of the engine DLL needs to be known when compiling the wrapper. Obviously, if I have to compile different versions of the wrapper for each project, this is quite cumbersome. The engine could run as a separate process. This means that the wrapper would launch a separate process for the engine when it loads a project, and it would use some form of IPC to communicate with this process. While this is a relatively clean solution, it requires some effort to get working, I don't now which IPC technology would be best to set-up this kind of construction. There may also be a significant overhead of the communication: the engine needs to frequently exchange arrays of floating-point numbers. The engine could be adapted to support multiple projects. This means that the global variables should be put into a project structure, and every reference to the globals should be converted to a corresponding reference that is relative to a particular project. There are about 20-30 global variables, but as you can imagine, these global variables are referenced from all over the code base, so this conversion would need to be done in some automatic manner. A related problem is that you should be able to reference the "current" project structure in all places, but passing this along as an extra argument in each and every function signature is also cumbersome. Does there exist a technique (in C) to consider the current call stack and find the nearest enclosing instance of a relevant data value there? Can the stackoverflow community give some advice on these (or other) solutions?

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• embed a jquery script after jquery is loaded by widget

  - by matthew k

  http://stackoverflow.com/a/6065421 was helpful to see how to confirm jquery has been loaded. my widget will need a class that was written using jquery. may i have some assistance on embedding this other class built using jquery? thank you, below is the snippet from the above link with my code added in the final portion as noted in the code comments: (function(window, document, version, callback) { var j, d; var loaded = false; if (!(j = window.jQuery) || version > j.fn.jquery || callback(j, loaded)) { var script = document.createElement("script"); script.type = "text/javascript"; script.src = "/media/jquery.js"; script.onload = script.onreadystatechange = function() { if (!loaded && (!(d = this.readyState) || d == "loaded" || d == "complete")) { callback((j = window.jQuery).noConflict(1), loaded = true); j(script).remove(); } }; document.documentElement.childNodes[0].appendChild(script) } })(window, document, "1.3", function($, jquery_loaded) { //my code added below var script_tag = document.createElement('script'); script_tag.setAttribute("type","text/javascript"); script_tag.setAttribute("src", "http://mysite.com/widget/slides.jquery.js"); (document.getElementsByTagName("head")[0] || document.documentElement).appendChild(script_tag); $('#slides').slides({}); //this line gives an error. }); right now, i am trying the following based on the response(s) provided to this question (line that throws error is noted with a comment): //this function is called after jquery being embedded has been confirmed. {mysite} placeholder is nonexistent in actual code. function main() { jQuery(document).ready(function($) { var css_link = $("<link>", { rel: "stylesheet", type: "text/css", href: "http://mysite/widget/widget.css" }); css_link.appendTo('head'); $('#crf_widget').after('<div id="crf_widget_container"></div>'); /******* Load HTML *******/ var jsonp_url = "http://mysite/widget.php?callback=?"; $.getJSON(jsonp_url, function(data) { $('#crf_widget_container').html(data); $('#category_sel').change(function(){ alert(this.value); }); $.getScript("http://mysite/widget/slides.jquery.js", function(data, textStatus, jqxhr) { alert(1); //fires ok $('#slides').slides({}); //errors }); }); }); }

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• Why is my namespace not recognized in Visual Studio / xaml

  - by msfanboy

  Hello, these are my 2 classes a Attachable Property SelectedItems: code is from here: http://stackoverflow.com/questions/1297643/sync-selecteditems-in-a-muliselect-listbox-with-a-collection-in-viewmodel The namespace TBM.Helper is for sure proper as it works for other classes too. The namespace reference is also in the xaml file: xmlns:Helper="clr_namespace:TBM.Helper" But <ListBox Helper:SelectedItems.Items="{Binding SelectedItems}" ... does not work because = The property 'SelectedItems.Items' does not exist in XML namespace 'clr_namespace:TBM.Helper'. The attachable property 'Items' was not found in type 'SelectedItems What do I have to change ? using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Windows.Controls; using System.Collections; using System.Windows; namespace TBM.Helper { public static class SelectedItems : DependencyObject { private static readonly DependencyProperty SelectedItemsBehaviorProperty = DependencyProperty.RegisterAttached( "SelectedItemsBehavior", typeof(SelectedItemsBehavior), typeof(ListBox), null); public static readonly DependencyProperty ItemsProperty = DependencyProperty.RegisterAttached( "Items", typeof(IList), typeof(SelectedItems), new PropertyMetadata(null, ItemsPropertyChanged)); public static void SetItems(ListBox listBox, IList list) { listBox.SetValue(ItemsProperty, list); } public static IList GetItems(ListBox listBox) { return listBox.GetValue(ItemsProperty) as IList; } private static void ItemsPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { var target = d as ListBox; if (target != null) { GetOrCreateBehavior(target, e.NewValue as IList); } } private static SelectedItemsBehavior GetOrCreateBehavior(ListBox target, IList list) { var behavior = target.GetValue(SelectedItemsBehaviorProperty) as SelectedItemsBehavior; if (behavior == null) { behavior = new SelectedItemsBehavior(target, list); target.SetValue(SelectedItemsBehaviorProperty, behavior); } return behavior; } } } using System.Windows; using System.Windows.Controls; using System.Collections; namespace TBM.Helper { public class SelectedItemsBehavior { private readonly ListBox _listBox; private readonly IList _boundList; public SelectedItemsBehavior(ListBox listBox, IList boundList) { _boundList = boundList; _listBox = listBox; SetSelectedItems(); _listBox.SelectionChanged += OnSelectionChanged; _listBox.DataContextChanged += OnDataContextChanged; } private void SetSelectedItems() { _listBox.SelectedItems.Clear(); foreach (object item in _boundList) { // References in _boundList might not be the same as in _listBox.Items int i = _listBox.Items.IndexOf(item); if (i >= 0) _listBox.SelectedItems.Add(_listBox.Items[i]); } } private void OnDataContextChanged(object sender, DependencyPropertyChangedEventArgs e) { SetSelectedItems(); } private void OnSelectionChanged(object sender, SelectionChangedEventArgs e) { _boundList.Clear(); foreach (var item in _listBox.SelectedItems) _boundList.Add(item); } } }

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• Click on notification starts activity twice

  - by Karussell

  I'm creating a notification from a service with the following code: NotificationManager notificationManager = (NotificationManager) ctx .getSystemService(Context.NOTIFICATION_SERVICE); CharSequence tickerText = "bla ..."; long when = System.currentTimeMillis(); Notification notification = new Notification(R.drawable.icon, tickerText, when); Intent notificationIntent = new Intent(ctx, SearchActivity.class). putExtra(SearchActivity.INTENT_SOURCE, MyNotificationService.class.getSimpleName()); PendingIntent contentIntent = PendingIntent.getActivity(ctx, 0, notificationIntent, 0); notification.setLatestEventInfo(ctx, ctx.getString(R.string.app_name), tickerText, contentIntent); notification.flags |= Notification.FLAG_AUTO_CANCEL; notificationManager.notify(1, notification); The logs clearly says that the the method startActivity is called twice times: 04-02 23:48:06.923: INFO/ActivityManager(2466): Starting activity: Intent { act=android.intent.action.SEARCH cmp=com.xy/.SearchActivity bnds=[0,520][480,616] (has extras) } 04-02 23:48:06.923: WARN/ActivityManager(2466): startActivity called from non-Activity context; forcing Intent.FLAG_ACTIVITY_NEW_TASK for: Intent { act=android.intent.action.SEARCH cmp=com.xy/.SearchActivity bnds=[0,520][480,616] (has extras) } 04-02 23:48:06.958: INFO/ActivityManager(2466): Starting activity: Intent { act=android.intent.action.SEARCH cmp=com.xy/.SearchActivity bnds=[0,0][480,96] (has extras) } 04-02 23:48:06.958: WARN/ActivityManager(2466): startActivity called from non-Activity context; forcing Intent.FLAG_ACTIVITY_NEW_TASK for: Intent { act=android.intent.action.SEARCH cmp=com.xy/.SearchActivity bnds=[0,0][480,96] (has extras) } 04-02 23:48:07.087: INFO/notification(5028): onStartCmd: received start id 2: Intent { cmp=com.xy/.NotificationService } 04-02 23:48:07.310: INFO/notification(5028): onStartCmd: received start id 3: Intent { cmp=com.xy/.NotificationService } 04-02 23:48:07.392: INFO/ActivityManager(2466): Displayed activity com.xy/.SearchActivity: 462 ms (total 462 ms) 04-02 23:48:07.392: INFO/ActivityManager(2466): Displayed activity com.xy/.SearchActivity: 318 ms (total 318 ms) Why are they started twice? There are two identical questions on stackoverflow: here and here. But they do not explain what the initial issue could be and they do not work for me. E.g. changing to launchMode singleTop is not appropriated for me and it should work without changing launchMode according to the official docs (see Invoking the search dialog). Nevertheless I also tried to add the following flags to notificationIntent Intent.FLAG_ACTIVITY_CLEAR_TOP | PendingIntent.FLAG_UPDATE_CURRENT but the problem remains the same.

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• Scalable Database Tagging Schema

  - by Longpoke

  EDIT: To people building tagging systems. Don't read this. It is not what you are looking for. I asked this when I wasn't aware that RDBMS all have their own optimization methods, just use a simple many to many scheme. I have a posting system that has millions of posts. Each post can have an infinite number of tags associated with it. Users can create tags which have notes, date created, owner, etc. A tag is almost like a post itself, because people can post notes about the tag. Each tag association has an owner and date, so we can see who added the tag and when. My question is how can I implement this? It has to be fast searching posts by tag, or tags by post. Also, users can add tags to posts by typing the name into a field, kind of like the google search bar, it has to fill in the rest of the tag name for you. I have 3 solutions at the moment, but not sure which is the best, or if there is a better way. Note that I'm not showing the layout of notes since it will be trivial once I get a proper solution for tags. Method 1. Linked list tagId in post points to a linked list in tag_assoc, the application must traverse the list until flink=0 post: id, content, ownerId, date, tagId, notesId tag_assoc: id, tagId, ownerId, flink tag: id, name, notesId Method 2. Denormalization tags is simply a VARCHAR or TEXT field containing a tab delimited array of tagId:ownerId. It cannot be a fixed size. post: id, content, ownerId, date, tags, notesId tag: id, name, notesId Method 3. Toxi (from: http://www.pui.ch/phred/archives/2005/04/tags-database-schemas.html, also same thing here: http://stackoverflow.com/questions/20856/how-do-you-recommend-implementing-tags-or-tagging) post: id, content, ownerId, date, notesId tag_assoc: ownerId, tagId, postId tag: id, name, notesId Method 3 raises the question, how fast will it be to iterate through every single row in tag_assoc? Methods 1 and 2 should be fast for returning tags by post, but for posts by tag, another lookup table must be made. The last thing I have to worry about is optimizing searching tags by name, I have not worked that out yet. I made an ASCII diagram here: http://pastebin.com/f1c4e0e53

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• how to update an Android ListActivity on changing data of the connected SimpleCursorAdapter

  - by 4485670

  I have the following code. What I want to achieve is to update the shown list when I click an entry so I can traverse through the list. I found the two uncommented ways to do it here on stackoverflow, but neither works. I also got the advice to create a new ListActivity on the data update, but that sounds like wasting resources? EDIT: I found the solution myself. All you need to do is call "SimpleCursorAdapter.changeCursor(new Cursor);". No notifying, no things in UI-Thread or whatever. import android.app.ListActivity; import android.database.Cursor; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.ListView; import android.widget.SimpleCursorAdapter; public class MyActivity extends ListActivity { private DepartmentDbAdapter mDbHelper; private Cursor cursor; private String[] from = new String[] { DepartmentDbAdapter.KEY_NAME }; private int[] to = new int[] { R.id.text1 }; private SimpleCursorAdapter notes; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.departments_list); mDbHelper = new DepartmentDbAdapter(this); mDbHelper.open(); // Get all of the departments from the database and create the item list cursor = mDbHelper.fetchSubItemByParentId(1); this.startManagingCursor(cursor); // Now create an array adapter and set it to display using our row notes = new SimpleCursorAdapter(this, R.layout.department_row, cursor, from, to); this.setListAdapter(notes); } @Override protected void onListItemClick(ListView l, View v, int position, long id) { super.onListItemClick(l, v, position, id); // get new data and update the list this.updateData(safeLongToInt(id)); } /** * update data for the list * * @param int departmentId id of the parent department */ private void updateData(int departmentId) { // close the old one, get a new one cursor.close(); cursor = mDbHelper.fetchSubItemByParentId(departmentId); // change the cursor of the adapter to the new one notes.changeCursor(cursor); } /** * safely convert long to in to save memory * * @param long l the long variable * * @return integer */ public static int safeLongToInt(long l) { if (l < Integer.MIN_VALUE || l > Integer.MAX_VALUE) { throw new IllegalArgumentException (l + " cannot be cast to int without changing its value."); } return (int) l; } }

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• Design patterns and interview question

  - by user160758

  When I was learning to code, I read up on the design patterns like a good boy. Long after this, I started to actually understand them. Design discussions such as those on this site constantly try to make the rules more and more general, which is good. But there is a line, over which it becomes over-analysis starts to feed off itself and as such I think begins to obfuscate the original point - for example the "What's Alternative to Singleton" post and the links contained therein. http://stackoverflow.com/questions/1300655/whats-alternative-to-singleton I say this having been asked in both interviews I’ve had over the last 2 weeks what a singleton is and what criticisms I have of it. I have used it a few times for items such as user data (simple key-value eg. last file opened by this user) and logging (very common i'm sure). I've never ever used it just to have what is essentially global application data, as this is clearly stupid. In the first interview, I reply that I have no criticisms of it. He seemed disappointed by this but as the job wasn’t really for me, I forgot about it. In the next one, I was asked again and, as I wanted this job, I thought about it on the spot and made some objections, similar to those contained in the post linked to above (I suggested use of a factory or dependency injection instead). He seemed happy with this. But my problem is that I have used the singleton without ever using it in this kind of stupid way, which I had to describe on the spot. Using it for global data and the like isn’t something I did then realised was stupid, or read was stupid so didn’t do, it was just something I knew was stupid from the start. Essentially I’m supposed to be able to think of ways of how to misuse a pattern in the interview? Which class of programmers can best answer this question? The best ones? The medium ones? I'm not sure.... And these were both bright guys. I read more than enough to get better at my job but had never actually bothered to seek out criticisms of the most simple of the design patterns like this one. Do people think such questions are valid and that I ought to know the objections off by heart? Or that it is reasonable to be able to work out what other people who are missing the point would do on the fly? Or do you think I’m at least partially right that the question is too unsubtle and that the questions ought to be better thought out in order to make sure only good candidates can answer. PS. Please don’t think I’m saying that I’m just so clever that I know everything automatically - I’ve learnt the hard way like everyone else. But avoiding global data is hardly revolutionary.

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• Using IOperationBehavior to supply a WCF parameter

  - by Chris Kemp

  This is my first step into the world of stackoverflow, so apologies if I cock anything up. I'm trying to create a WCF Operation which has a parameter that is not exposed to the outside world, but is instead automatically passed into the function. So the world sees this: int Add(int a, int b) But it is implemented as: int Add(object context, int a, int b) Then, the context gets supplied by the system at run-time. The example I'm working with is completely artificial, but mimics something that I'm looking into in a real-world scenario. I'm able to get close, but not quite the whole way there. First off, I created a simple method and wrote an application to confirm it works. It does. It returns a + b and writes the context as a string to my debug. Yay. [OperationContract] int Add(object context, int a, int b); I then wrote the following code: public class SupplyContextAttribute : Attribute, IOperationBehavior { public void Validate(OperationDescription operationDescription) { if (!operationDescription.Messages.Any(m => m.Body.Parts.First().Name == "context")) throw new FaultException("Parameter 'context' is missing."); } public void ApplyDispatchBehavior(OperationDescription operationDescription, DispatchOperation dispatchOperation) { dispatchOperation.Invoker = new SupplyContextInvoker(dispatchOperation.Invoker); } public void ApplyClientBehavior(OperationDescription operationDescription, ClientOperation clientOperation) { } public void AddBindingParameters(OperationDescription operationDescription, BindingParameterCollection bindingParameters) { // Remove the 'context' parameter from the inbound message operationDescription.Messages[0].Body.Parts.RemoveAt(0); } } public class SupplyContextInvoker : IOperationInvoker { readonly IOperationInvoker _invoker; public SupplyContextInvoker(IOperationInvoker invoker) { _invoker = invoker; } public object[] AllocateInputs() { return _invoker.AllocateInputs().Skip(1).ToArray(); } private object[] IntroduceContext(object[] inputs) { return new[] { "MyContext" }.Concat(inputs).ToArray(); } public object Invoke(object instance, object[] inputs, out object[] outputs) { return _invoker.Invoke(instance, IntroduceContext(inputs), out outputs); } public IAsyncResult InvokeBegin(object instance, object[] inputs, AsyncCallback callback, object state) { return _invoker.InvokeBegin(instance, IntroduceContext(inputs), callback, state); } public object InvokeEnd(object instance, out object[] outputs, IAsyncResult result) { return _invoker.InvokeEnd(instance, out outputs, result); } public bool IsSynchronous { get { return _invoker.IsSynchronous; } } } And my WCF operation now looks like this: [OperationContract, SupplyContext] int Amend(object context, int a, int b); My updated references no longer show the 'context' parameter, which is exactly what I want. The trouble is that whenver I run the code, it gets past the AllocateInputs and then throws an Index was outside the bounds of the Array. error somewhere in the WCF guts. I've tried other things, and I find that I can successfully change the type of the parameter and rename it and have my code work. But the moment I remove the parameter it falls over. Can anyone give me some idea of how to get this to work (or if it can be done at all).

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• c++ class member functions instatiated by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched stackoverflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state info was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (vc++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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• How does the event dispatch thread work?

  - by Roman

  With the help of people on stackoverflow I was able to get the following working code of the simples GUI countdown (it just displays a window counting down seconds). My main problem with this code is the invokeLater stuff. As far as I understand the invokeLater send a task to the event dispatching thread (EDT) and then the EDT execute this task whenever it "can" (whatever it means). Is it right? To my understanding the code works like that: In the main method we use invokeLater to show the window (showGUI method). In other words, the code displaying the window will be executed in the EDT. In the main method we also start the counter and the counter (by construction) is executed in another thread (so it is not in the event dispatching thread). Right? The counter is executed in a separate thread and periodically it calls updateGUI. The updateGUI is supposed to update GUI. And GUI is working in the EDT. So, updateGUI should also be executed in the EDT. It is why the code for the updateGUI is inclosed in the invokeLater. Is it right? What is not clear to me is why we call the counter from the EDT. Anyway it is not executed in the EDT. It starts immediately a new thread and the counter is executed there. So, why we cannot call the counter in the main method after the invokeLater block? import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.SwingUtilities; public class CountdownNew { static JLabel label; // Method which defines the appearance of the window. public static void showGUI() { JFrame frame = new JFrame("Simple Countdown"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); label = new JLabel("Some Text"); frame.add(label); frame.pack(); frame.setVisible(true); } // Define a new thread in which the countdown is counting down. public static Thread counter = new Thread() { public void run() { for (int i=10; i>0; i=i-1) { updateGUI(i,label); try {Thread.sleep(1000);} catch(InterruptedException e) {}; } } }; // A method which updates GUI (sets a new value of JLabel). private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater( new Runnable() { public void run() { label.setText("You have " + i + " seconds."); } } ); } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { public void run() { showGUI(); counter.start(); } }); } }

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• DRY-ing very similar specs for ASP.NET MVC controller action with MSpec (BDD guidelines)

  - by spapaseit

  Hi all, I have two very similar specs for two very similar controller actions: VoteUp(int id) and VoteDown(int id). These methods allow a user to vote a post up or down; kinda like the vote up/down functionality for StackOverflow questions. The specs are: VoteDown: [Subject(typeof(SomeController))] public class When_user_clicks_the_vote_down_button_on_a_post : SomeControllerContext { Establish context = () => { post = PostFakes.VanillaPost(); post.Votes = 10; session.Setup(s => s.Single(Moq.It.IsAny<Expression<Func<Post, bool>>>())).Returns(post); session.Setup(s => s.CommitChanges()); }; Because of = () => result = controller.VoteDown(1); It should_decrement_the_votes_of_the_post_by_1 = () => suggestion.Votes.ShouldEqual(9); It should_not_let_the_user_vote_more_than_once; } VoteUp: [Subject(typeof(SomeController))] public class When_user_clicks_the_vote_down_button_on_a_post : SomeControllerContext { Establish context = () => { post = PostFakes.VanillaPost(); post.Votes = 0; session.Setup(s => s.Single(Moq.It.IsAny<Expression<Func<Post, bool>>>())).Returns(post); session.Setup(s => s.CommitChanges()); }; Because of = () => result = controller.VoteUp(1); It should_increment_the_votes_of_the_post_by_1 = () => suggestion.Votes.ShouldEqual(1); It should_not_let_the_user_vote_more_than_once; } So I have two questions: How should I go about DRY-ing these two specs? Is it even advisable or should I actually have one spec per controller action? I know I Normally should, but this feels like repeating myself a lot. Is there any way to implement the second It within the same spec? Note that the It should_not_let_the_user_vote_more_than_once; requires me the spec to call controller.VoteDown(1) twice. I know the easiest would be to create a separate spec for it too, but it'd be copying and pasting the same code yet again... I'm still getting the hang of BDD (and MSpec) and many times it is not clear which way I should go, or what the best practices or guidelines for BDD are. Any help would be appreciated.

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• Why doesn't TextBlock databinding call ToString() on a property whose compile-time type is an interf

  - by Jay

  This started with weird behaviour that I thought was tied to my implementation of ToString(), and I asked this question: http://stackoverflow.com/questions/2916068/why-wont-wpf-databindings-show-text-when-tostring-has-a-collaborating-object It turns out to have nothing to do with collaborators and is reproducible. When I bind Label.Content to a property of the DataContext that is declared as an interface type, ToString() is called on the runtime object and the label displays the result. When I bind TextBlock.Text to the same property, ToString() is never called and nothing is displayed. But, if I change the declared property to a concrete implementation of the interface, it works as expected. Is this somehow by design? If so, any idea why? To reproduce: Create a new WPF Application (.NET 3.5 SP1) Add the following classes: public interface IFoo { string foo_part1 { get; set; } string foo_part2 { get; set; } } public class Foo : IFoo { public string foo_part1 { get; set; } public string foo_part2 { get; set; } public override string ToString() { return foo_part1 + " - " + foo_part2; } } public class Bar { public IFoo foo { get { return new Foo {foo_part1 = "first", foo_part2 = "second"}; } } } Set the XAML of Window1 to: <Window x:Class="WpfApplication1.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window1" Height="300" Width="300"> <StackPanel> <Label Content="{Binding foo, Mode=Default}"/> <TextBlock Text="{Binding foo, Mode=Default}"/> </StackPanel> </Window> in Window1.xaml.cs: public partial class Window1 : Window { public Window1() { InitializeComponent(); DataContext = new Bar(); } } When you run this application, you'll see the text only once (at the top, in the label). If you change the type of foo property on Bar class to Foo (instead of IFoo) and run the application again, you'll see the text in both controls.

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