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  • What is the common way to program action listeners?

    - by Roman
    I just started to learn how to use action listeners. To my understanding it works in the following way: There are some classes which contains "addActionListener" method by default (for example classes for buttons). Using this method we add an action listener to an object. For example: listenedObject.addActionListener(listeningObject). When an action with the "listenedObject" is performed, the "actionPerformed" method of the "listeningObject" will be called. So, it means that when we program a class for the listeningObject, we need to put there "actionPerformed" method. What is not clear to me, should we create a new class for every object that we want to listen. It does not seem to me as an elegant solution. On the other hand, if we have one action listener class for all (or at least many) object, than we have a problem since a instance of this class will not know which object is calling the "actionPerformed" method (and we need to know that since actions performed by the actionPerformed differs depending on who is called for this method). In my opinion, for every listened object we need to create are "personal" action listener and we can do it by setting a specific value to the corresponding field of the action listener. But I am not sure that it is a standard way to go? How do usually people do it?

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  • RegExpValidator never matches

    - by babyangel86
    Hi, I've got a class that's meant to validate input fields to make sure the value is always a decimal. I've tested the regex here: http://livedocs.adobe.com/flex/3/html/help.html?content=validators_7.html, and it looks like it does the right thing, but in my app, I can't seem to get it to match to a number format. Class Definition: public class DecimalValidator { //------------------------------- ATTRIBUTES public var isDecimalValidator:RegExpValidator; //------------------------------- CONSTRUCTORS public function DecimalValidator() { isDecimalValidator = new RegExpValidator(); isDecimalValidator.expression = "^-?(\d+\.\d*|\.\d+)$"; isDecimalValidator.flags = "g"; isDecimalValidator.required = true; isDecimalValidator.property = "text"; isDecimalValidator.triggerEvent = FocusEvent.FOCUS_OUT; isDecimalValidator.noMatchError = "Float Expected"; } } Setting the source here: public function registerDecimalInputValidator(inputBox:TextInput, valArr:Array):void { // Add Validators var dValidator:DecimalValidator = new DecimalValidator(); dValidator.isDecimalValidator.source = inputBox; dValidator.isDecimalValidator.trigger = inputBox; inputBox.restrict = "[0-9].\\.\\-"; inputBox.maxChars = 10; valArr.push(dValidator.isDecimalValidator); } And Calling it here: registerDecimalInputValidator(textInput, validatorArr); Where textInput is an input box created earlier. Clearly I'm missing something simple yet important, but I'm not entirely sure what! Any help would be much appreciated.

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  • Simple Oracle File repository with folder hierarchy

    - by Ope
    I have an application that stores large amount of files (XML and binary) in folder hierarchies. Currently the main method is storing them in file system or using a legacy CMS, which we want to get rid of. The CMS supports Oracle and a customer wants to keep the files in Oracle because of enterprise policies (backup etc.) The question is: Is there a simple implementation of file repository with folder hierarchy for Oracle? What I am looking for is a small .Net component or example code (PL/SQL and/or .Net) that would have the following methods: Create, Delete, Exists Folder CRUD file Move and potentially Copy file or directory Access to files and folders with paths like "/root/folder1/folder2/file.xml" Ability to get all the files and folders in a folder and potentially also the entire directory tree Tree traversal, getting the parent, all children etc. needs to be fast. I need the implementation in .Net, but if it was just the stored procedures, I could create the .Net calling code. I have pointers to generic articles for creating hierarchies in DB, so if I need to do it from scratch, I know where to start. What I am asking here, is there already an implementation that I could take without doing this from scratch? It seems like such a generic requirement... If the answer is a CMS, Document management system or such it should be Open Source or at least quite cheap (some hundreds / server) and it should be possible to deploy it XCopy - hopefully only couple of DLL:s. I do not need - or want - a full featured big CMS with dozens of dlls and especially not an msi-installation. I have tried to google this, but the words "repository", "CMS", "file hierarchy" etc. give so many answers, the searches are pretty much useless. Thanks, OPe

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  • destructor being called by subclass

    - by zero
    I'm currently learning more about php objects and constructors/destructors, but i've noticed in my code that the parent class's destructor is being called twice, I thought it was because i was extending the first class to my second class and that the second class was calling it, but this is what the php docs say about that: Like constructors, parent destructors will not be called implicitly by the engine. In order to run a parent destructor, one would have to explicitly call parent::__destruct() in the destructor body. so if it is not being called by the subclass then is it because by extended the first class that i've made a reference to the parent class making it call itself twice or I'm I way off base here? the code: <?php class test{ public $test1 = "this is a test of a pulic property"; private $test2 = "this is a test of a private property"; protected $test3 = "this is a test of a protected property"; const hello = 900000; function __construct($h){ //echo 'this is the constructor test '.$h; } function x($x2){ echo ' this is fn x'.$x2; } function y(){ print "this is fn y"; } } $obj = new test("this is an \"arg\" sent to instance of test"); class hey extends test{ function hey(){ $this->x('<br>from the host with the most'); echo ' <br>from hey class'.$this->test3; } } $obj2 = new hey(); echo $obj2::hello; ?>

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  • jquery ajax problem in chrome

    - by spaceman
    i have the following jquery code running on my page just fine in FF and IE, but chrome seems to be freaking out.. in FF and IE the call is made and the result is appended to the div. in chrome, it calls ajaxfailed on failure. the XMLHttpRequest passed to the AjaxFailed function has a status code of "200" and the statusText is "ok". the readystate is 4 and the responseText is set to the data i wish to append to the div.. basically from what i can see its calling the failure method but it isn't failing.. i have tried with both get and post requests and it always breaks in chrome. function getBranchDetails(contactID, branchID) { $.ajax({ type: "GET", url: urlToRequestTo, data: "{}", contentType: "application/json; charset=utf-8", dataType: "json", success: branchDetailsSuccess, error: AjaxFailed }); } function branchDetailsSuccess(result) { $("#divBranchControl").empty(); $("#divBranchControl").append(" " + result); $("#branchDiv").tabs(); } function AjaxFailed(result) { alert("FAILED : " + result.status + ' ' + result.statusText); }

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  • What is a good RPC model for building a AJAX web app using PHP & JS?

    - by user366152
    I'm new to writing AJAX applications. I plan on using jQuery on the client side while PHP on the server side. I want to use something like XML-RPC to simplify my effort in calling server-side code. Ideally, I wouldn't care whether the transport layer uses XML or JSON or a format more optimized for the wire. If I was writing a console app I'd use some tool to generate function stubs which I would then implement on the RPC server while the client would natively call into those stubs. This provides a clean separation. Is there something similar available in the AJAX world? While on this topic, how would I proceed with session management? I would want it to be as transparent as possible. For example, if I try to hit an RPC end-point which needs a valid session, it should reject the request if the client doesn't pass a valid session cookie. This would really ease my application development. I'd then have to simply handle the frontend using native JS functions. While on the backend, I can simply implement the RPC functions. BTW I dont wish to use Google Web Toolkit. My app wont be extremely heavy on AJAX.

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  • POSIX Sockets: How to detect Ctrl-C sent over Telnet?

    - by ogott
    Short Question What's the right way to handle a Ctrl-C event sent over Telnet on the server side? Long Question After calling recv() on a socket, I'd like to handle some situations appropriately. One of them is to return a certain error code when Ctrl-C was received. What's the correct way to detect this? The following works, but it just doesn't seem right: size_t recv_count; static char ctrl_c[5] = {0xff, 0xf4, 0xff, 0xfd, 0x06}; recv_count = recv(socket, buffer, buffer_size, 0); if (recv_count == sizeof(ctrl_c) && memcmp(buffer, ctrl_c, sizeof(ctrl_c) == 0) { return CTRL_C_RECEIVED; } I found a comment on Ctrl-C in a side-note in this UNIX Socket FAQ: [...] (by the way, out-of-band is often used for that ctrl-C, too). As I understand, receiving out-of-band data is done using recv() with a certain flag as the last parameter. But when I'm waiting for data using recv() as I do in the code above, I can't read out-of-band data at the same time. Apart from that, I'm getting something using recv() without that oob-flag.

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  • redirecting _top page from asp:login control in iframe onloggedin

    - by jumpdart
    So yeah, Im building a little authenticated content(.NET app) to a large html site managed by another group. They are only comfortable with managing html so all my app content will be contained in iframes. Everything is working fine as far as navigation and calling services and whatnot but i cant bust out of the frame with my asp:login control. Im trying to register some JS on logged in but with no success. Thanks protected void login_LoggedIn(object sender, EventArgs e) { StringBuilder strScript = new StringBuilder(); strScript.Append("<script language='javascript'>"); string sHome = ConfigurationManager.AppSettings["AppHomePageURL"].ToString(); //strScript.AppendFormat("window.navigate('{0}');", sHome); //strScript.AppendFormat("parent.location.href='{0}';", sHome); //strScript.AppendFormat("window.open('{0}', '_top', '', false);", sHome); strScript.AppendFormat("top.location.href='{0}';", sHome); strScript.Append("WTF_let_me_outa_here();"); strScript.Append("</script>"); ClientScript.RegisterClientScriptBlock(typeof(Page), "LoginGO", strScript.ToString()); }

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  • Game design flaw, need help investigating

    - by Snake
    I am not sure if I will be able to get help here but I would give it a shot. The problem is I dont know where the problem is. I have a cards game, in which when you "human" play by dragging a card, then at the end of card being dragged, a handler using postExecute is called with delay of 0.5 sec to start the next player in turn (which is a bot) The bot chooses the color and plays it and at the end of the animation (the card moving to the middle) a handler is started for the next bot and so on. Once the play reaches again to the human player, it waits for his touchs to drag the crad and start the cycle again. The problem that in production, sometimes I am getting errors. The error is resulting in somehow messing up the sequence which ends up with players having more cards than others. After investigation, I found that the transition from human to bot is the problem. Somehow, the transition is happening twice (meaning handler calling post execute twice and the bot is playing twice and everything is messed up). Its been mutliple months and I can't reproduce it (to fix it) and I cna't figure out why this is happeneing? ANY IDEA how I can go after it? How can I get more info about or how can I solve something like that? any pointer would help me

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  • javascript error handling

    - by pankaj
    I have a javascript function for checking errors which I am calling on OnClicentClick event of a button. Once it catch a error I want to stop execution of the click event. But in my case it always it always executes the onclick event. Following is my function: function DisplayError() { if (document.getElementById('<%=txtPassword.ClientID %>').value.length < 6 || document.getElementById('<%=txtPassword.ClientID %>').value.length > 12) { document.getElementById('<%=lblError.ClientID %>').innerText = "Password length must be between 6 to 12 characters"; return false; } var str = <%=PhoneNumber()%>; if(str.length <10) { alert('<%=phoneNum%>'.length); document.getElementById('<%=lblError.ClientID %>').innerText = "Phone Number not in correct format"; return false; } } button html code: <asp:Button runat="server" Text="Submit" ID="btnSubmit" ValidationGroup="submit" onclick="btnSubmit_Click" OnClientClick="DisplayError()"/> It should not execute the button click event once it satisfies any of the IF condition in the javascript function.

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  • PHP delete script, return to 'viewsubjects.php?classroom_id=NO VALUE'

    - by Derek
    Hi, As the title states... I am deleting a 'subject' from a 'classroom' I view classrooms, then can click on a classroom to view the subject for that classroom. So the link where I am viewing subjects looks like: viewsubjects.php?classroom=23 When the user selects the delete button (in a row) to remove a subject from a class, I simply want the user to be redirected back to the list of subjects for the classroom (exactly where they were before!!) So I though this is simply a case of calling up the classroom ID within my delete script. Here is what I have: EDIT: corrected spelling mistake in code (this was not the problem) $subject_id = $_GET['subject_id']; $classroom_id = $_GET['classroom_id']; $sql = "DELETE FROM subjects WHERE subject_id=".$subject_id; $result = mysql_query($sql, $connection) or die("MySQL Error: ".mysql_error()); header("Location: viewsubjects.php?classroom_id=".$classroom_id); exit(); The subject is being removed from the DB, but when I am redirected back the URI is displaying with an empty classroom ID like: viewsubjects.php?classroom_id= Is there a way to carry the classroom ID through successfully through the delete script so it can be displayed after, allowing the user to be redirected back to the page? Thanks for any help!

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  • free( ) pointers

    - by user1043625
    I'm required to use a special library to keep track of my memory leaks where malloc()= allocate( ) and free( ) = unallocate( ). I'm trying to complete free a linked-list but it seems like the "root" value isn't being freed. typedef struct _node { struct _node *child; char *command; } Command_list; void delete_commands(Command_list **root) { Command_list *temp; while( *root != NULL ){ temp = (*root)->child; //printf("STRING: %s\n", *root->command ); unallocate( *root ); *root = temp; } } The function that's calling it void file_processing( .... ){ Command_list *root = allocate(sizeof (Command_list)); root = NULL; .... delete_commands( &root ); } } I believe that Command_list *root = allocate(sizeof (Command_list)) isn't being properly de-allocated for some reason. Anyone can give me some hints? UPDATE: I found out that instead of Command_list *root = allocate(sizeof (Command_list)); root = NULL; this works: Command_list *root = NULL;

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  • Is this an error in "More Effective C++" in Item28?

    - by particle128
    I encountered a question when I was reading the item28 in More Effective C++ .In this item, the author shows to us that we can use member template in SmartPtr such that the SmartPtr<Cassette> can be converted to SmartPtr<MusicProduct>. The following code is not the same as in the book,but has the same effect. #include <iostream> class Base{}; class Derived:public Base{}; template<typename T> class smart{ public: smart(T* ptr):ptr(ptr){} template<typename U> operator smart<U>() { return smart<U>(ptr); } ~smart(){delete ptr;} private: T* ptr; }; void test(const smart<Base>& ) {} int main() { smart<Derived> sd(new Derived); test(sd); return 0; } It indeed can be compiled without compilation error. But when I ran the executable file, I got a core dump. I think that's because the member function of the conversion operator makes a temporary smart, which has a pointer to the same ptr in sd (its type is smart<Derived>). So the delete directive operates twice. What's more, after calling test, we can never use sd any more, since ptr in sd has already been delete. Now my questions are : Is my thought right? Or my code is not the same as the original code in the book? If my thought is right, is there any method to do this? Thanks very much for your help.

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  • multiplying all elements in an array by an outside number?

    - by prodo
    I need to multiple all the values in an array by 3000 which in turn would create a new array that I will use to subtract from another array. I've tried to create a separate method that would do that for me but all I got back in the multiplied array was a bunch of numbers and symbols strangely? here is the code that I wrote public static void main(String[] args) { int numberOfTaxpayers = Integer.parseInt(JOptionPane.showInputDialog("Enter how many users you would like to calculate taxes for: "); int[] usernumChild = new int[numberOfTaxPayers]; for (int i = 0; i < usernumChild.length; i++) { usernumChild[i] = Integer.parseInt(JOptionPane.showInputDialog("Enter number of children for user "+ (i+1) +": ")); }//this for loop finds out the number of children per user so we can later multiply each input by 3000 to create an array that determine dependency exemption for each user int[] depndExemp = multiply(usernumChild, 3000);//this was the calling of the multiply method... somewhere here is the error!! }//end main method public static int[] multiply(int[] children, int number) { int array[] = new int[children.length]; for( int i = 0; i < children.length; i++) { children[i] = children[i] * number; }//end for return array; }//this is the method that I was shown in a previous post on how to create return an array in this the dependency exemption array but when I tested this by printing out the dependency array all I received were a jumble of wrong numbers.

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  • math.Random isn't working right

    - by RandomlyKnighted
    I'm trying to simulate a coin flip using the code below. public class Coin { public static double result; int[] count = new count[2]; public static void flip() { result = Math.random(); } public static boolean isHeads() { if (result == 0.0) { count[0]++; return false; } else { count[1]++; return true; } } public static void main(String[] args) { flip(); isHeads(); System.out.println(count[0]); System.out.println(count[1]); } } For some reason Eclipse says that the import java.util.Random; is never used even though I'm clearly using it. I didn't put my for loop into the code above but it loops n number of times and then outputs the result. No matter how many times it loops it always returns that the result is greater than 0.0 which can't be right. Am I calling Math.random incorrectly?

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  • How can I put back a character that I've read when I detect it's the start of a new row?

    - by gcc
    char nm; int i=0; double thelow, theupp; double numbers[200]; for(i=0;i<4;++i) { { char nm; double thelow,theupp; /*after erased ,created again*/ scanf("%c %lf %lf", &nm, &thelow, &theupp); for (k = 0; ; ++k) ; { scanf("%lf",numbers[k]); if(numbers[k]=='\n') break; } /*calling function and sending data(nm,..) to it*/ } /*after } is seen (nm ..) is erased*/ ; } I want say compiler : hey my dear code read only i-th row,dont touch characters at placed in next line. because characters at placed in next line is token after i increased by 1 and nm ,thelow,theupp is being zero or erased after then again created. how can I do ? input; D -1.5 0.5 .012 .025 .05 .1 .1 .1 .025 .012 0 0 0 .012 .025 .1 .2 .1 .05 .039 .025 .025 B 1 3 .117 .058 .029 .015 .007 .007 .007 .015 .022 .029 .036 .044 .051 .058 .066 .073 .080 .088 .095 .103

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  • Add a smaller subView with new origin

    - by ReachWest
    I can't get my head around this - I know it must be simple.. I'm starting to feel pretty stupid. I have two viewControllers. MainViewController.h/m and LevelsViewController.h/m I want to add a subView from the LevelsViewController class and a view that is built in IB called levelsView. I am calling this from the MainViewController.m file. The levelsView is only 200x200 pixels and I want to offset it from the frame origin of the superView by x=140 pixels and y=50 pixels. I have this working - the view displays, but I can't figure out how to offset it. It only shows up at the 0,0 superView frame origin. (The superView shows below it, which is what I want). Here is the code I call in the method in the MainViewController.m that displays the levelsView.(I have commented out some of the things I have tried - but throws this error: error: request for member 'frame' in 'myLevelsView', which is of non-class type 'LevelsViewController*' ) - (void) displayLevelsPage { if (self.theLevelsView == nil) // Does not yet exist - therefore create { LevelsViewController * myLevelsView = [[LevelsViewController alloc] initWithNibName:@"levelsView" bundle:[NSBundle mainBundle]]; NSLog(@"NEW theLevelsView instance created!"); CGRect frame2 = CGRectMake(140, 50, 200, 200); //myLevelsView.frame = frame2; self.theLevelsView = myLevelsView; [myLevelsView release]; } [self.view addSubview: theLevelsView.view]; NSLog(@"Levels View has been activated"); } Any insight would be appreciated.

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  • Kill process started with System.Diagnostic.Process.Start("FileName")

    - by PedroC88
    Hello; I am trying to create an app that will perform actions on specific times (much like the Windows Task Scheduler). I am currently using Process.Start() to lunch the file (or exe) required by the task. I am initiating a process by calling a file (an .mp3) and the process starts WMP (since it is the default application), so far so good. Now I wan't to kill that process. I know that it is normal behavior for the Process.Start(string, string) to return nothing (null in C#) in this case. So I am asking how can i close WMP when I called it through Process.Start(string, string)?? Edit: Please note that I am not opening WMP directly with Process.Start() and this is the line with which I run the process: VB: Me._procs.Add(Process.Start(Me._procInfo)) C#: this._procs.Add(Process.Start(this._procInfo)) _procInfo is a ProcessStartInfo instance. _procInfo.FileName is "C:\route\myFile.mp3". That is why WMP opens. In any case, all of the Start() methods, except for the instance-one which returns a boolean, return nothing (null in C#), because WMP is not the process that was directly created (please note that WMP is run and the song does play).

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  • Problems Expanding an Array in C++

    - by dxq
    I'm writing a simulation for class, and part of it involves the reproduction of organisms. My organisms are kept in an array, and I need to increase the size of the array when they reproduce. Because I have multiple classes for multiple organisms, I used a template: template <class orgType> void expandarray(orgType* oldarray, int& numitems, int reproductioncount) { orgType *newarray = new orgType[numitems+reproductioncount]; for (int i=0; i<numitems; i++) { newarray[i] = oldarray[i]; } numitems += reproductioncount; delete[] oldarray; oldarray = newarray; newarray = NULL; } However, this template seems to be somehow corrupting my data. I can run the program fine without reproduction (commenting out the calls to expandarray), but calling this function causes my program to crash. The program does not crash DURING the expandarray function, but crashes on access violation later on. I've written functions to expand an array hundreds of times, and I have no idea what I screwed up this time. Is there something blatantly wrong in my function? Does it look right to you? EDIT: Thanks for everyone's help. I can't believe I missed something so obvious. In response to using std::vector: we haven't discussed it in class yet, and as silly as it seems, I need to write code using the methods we've been taught.

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  • Adding a Click event to a submit button and then submitting the form

    - by Abs
    Hello all, I have a form with a submit button. I have attached a click event to that submit button using JQuery. Once I did this my form wasn't submitting, I thought this was because of the event I added- if I remove that click event it submits the form successfully. I have tried giving my form an id and calling the submit function but this was not successful either. What can I do? $('#submit_gen').click(function() { $('#genbtn').html('<img src="images/ajax-loader.gif" alt="loading" />'); $('#action_form').submit(); }); The HTML: <form id="action_form" action="generate.php" method="post" enctype="multipart/form-data"> <input id="file_upload" type="file" name="upload" onchange="file_select();"/> <input type="text" id="overlay_input"> <div id="genbtn" class="genbtn"> <input id="submit_gen" type="submit" value="Upload"> </div> </form> Thanks all

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  • Printing a JFrame and its components

    - by Alex Terreaux
    I have been working in a big program and one of its functionalities should be to print the contents of the main window. I checked the API and found this example: http://docs.oracle.com/javase/tutorial/2d/printing/gui.html it was very helpful, I tried to use that code in my program by placing this inside the actionperformed method of my print button: PrinterJob job = PrinterJob.getPrinterJob(); job.setPrintable(this); boolean ok = job.printDialog(); if (ok) { try { job.print(); } catch (PrinterException ex) { /* The job did not successfully complete */ } } If I click the print button, I get a printer dialog and when I tell it to print, it just prints a blank document. I know the above code is not all I need, as I've seen in the API's examples there is a print() method, but apparently they never call it, so it is pretty confusing. I've tried calling and using it many times, but with no success. Also, I think that when I finally get it to print, my window will need to be printed in the landscape orientation, it even may need some scaling. Any ideas on how to do that? I would like any useful help to help me implement this code successfully. I know I should be able to do it by myself just by checking the documentation (I've tried for almost 2 days now) but I can't get it to work. I've learned all the programming I know through the internet. Any help will be greatly appreciated.

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  • HTTPS causes jQuery to ignore request

    - by Josh
    I have an odd bug, this jQuery code executes correctly when calling the page via HTTP, but once I connect to the page via HTTPS it doesn't execute. The code basically tracks when a link is clicked. <html> <head> <title>Test Page</title> <script type="text/javascript" src="/scripts/jquery-1.4.2.min.js"></script> <script type="text/javascript"> $(document).ready( function() { $('.fbspb').click(function() { $.get("/services/lt.ashx?ac=fbspb"); return true; }); }); </script> </head> <body> <a href="http://www.facebook.com" class="fbspb" target="_blank">Facebook</a> </body> </html> I've tried updating the URL in the get use a full HTTPS path with no success. No error is raised when I try to HTTPS.

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  • Is it an good idea to make a wrapper specifically for a DateTime that respresents Now?

    - by Dirk Boer
    I have been noticing lately that is really nice to use a DateTime representing 'now' as an input parameter for your methods, for mocking and testing purposes. Instead of every method calling DateTime.UtcNow themselves, I do it once in the upper methods and forward it on the lower ones. So a lot of methods that need a 'now', have an input parameter DateTime now. (I'm using MVC, and try to detect a parameter called now and modelbind DateTime.UtcNow to it) So instead of: public bool IsStarted { get { return StartTime >= DateTime.UtcNow; } } I usually have: public bool IsStarted(DateTime now) { return StartTime >= now; } So my convention is at the moment, if a method has a DateTime parameter called now, you have to feed it with the current time. Of course this comes down to convention, and someone else can easily just throw some other DateTime in there as a parameter. To make it more solid and static-typed I am thinking about wrapping DateTime in a new object, i.e. DateTimeNow. So in one of the most upper layers I will convert the DateTime to a DateTimeNow and we will get compile errors when, someone tries to fiddle in a normal DateTime. Of course you can still workaround this, but at least if feels more that you are doing something wrong at point. Did anyone else ever went into this path? Are there any good or bad results on the long term that I am not thinking about?

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  • optimization math computation (multiplication and summing)

    - by wiso
    Suppose you want to compute the sum of the square of the differences of items: $\sum_{i=1}^{N-1} (x_i - x_{i+1})^2$, the simplest code (the input is std::vector<double> xs, the ouput sum2) is: double sum2 = 0.; double prev = xs[0]; for (vector::const_iterator i = xs.begin() + 1; i != xs.end(); ++i) { sum2 += (prev - (*i)) * (prev - (*i)); // only 1 - with compiler optimization prev = (*i); } I hope that the compiler do the optimization in the comment above. If N is the length of xs you have N-1 multiplications and 2N-3 sums (sums means + or -). Now suppose you know this variable: sum = $x_1^2 + x_N^2 + 2 sum_{i=2}^{N-1} x_i^2$ Expanding the binomial square: $sum_i^{N-1} (x_i-x_{i+1})^2 = sum - 2\sum_{i=1}^{N-1} x_i x_{i+1}$ so the code becomes: double sum2 = 0.; double prev = xs[0]; for (vector::const_iterator i = xs.begin() + 1; i != xs.end(); ++i) { sum2 += (*i) * prev; prev = (*i); } sum2 = -sum2 * 2. + sum; Here I have N multiplications and N-1 additions. In my case N is about 100. Well, compiling with g++ -O2 I got no speed up (I try calling the inlined function 2M times), why?

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  • Abstract away a compound identity value for use in business logic?

    - by John K
    While separating business logic and data access logic into two different assemblies, I want to abstract away the concept of identity so that the business logic deals with one consistent identity without having to understand its actual representation in the data source. I've been calling this a compound identity abstraction. Data sources in this project are swappable and various and the business logic shouldn't care which data source is currently in use. The identity is the toughest part because its implementation can change per kind of data source, whereas other fields like name, address, etc are consistently scalar values. What I'm searching for is a good way to abstract the concept of identity, whether it be an existing library, a software pattern or just a solid good idea of some kind is provided. The proposed compound identity value would have to be comparable and usable in the business logic and passed back to the data source to specify records, entities and/or documents to affect, so the data source must be able to parse back out the details of its own compound ids. Data Source Examples: This serves to provide an idea of what I mean by various data sources having different identity implementations. A relational data source might express a piece of content with an integer identifier plus a language specific code. For example. content_id language Other Columns expressing details of content 1 en_us 1 fr_ca The identity of the first record in the above example is: 1 + en_us However when a NoSQL data source is substituted, it might somehow represent each piece of content with a GUID string 936DA01F-9ABD-4d9d-80C7-02AF85C822A8 plus language code of a different standardization, And a third kind of data source might use just a simple scalar value. So on and so forth, you get the idea.

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