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• Help a CRUD programmer think about an "approval workflow"

  - by gerdemb

  I've been working on a web application that is basically a CRUD application (Create, Read, Update, Delete). Recently, I've started working on what I'm calling an "approval workflow". Basically, a request is generated for a material and then sent for approval to a manager. Depending on what is requested, different people need to approve the request or perhaps send it back to the requester for modification. The approvers need to keep track of what to approve what has been approved and the requesters need to see the status of their requests. As a "CRUD" developer, I'm having a hard-time wrapping my head around how to design this. What database tables should I have? How do I keep track of the state of the request? How should I notify users of actions that have happened to their requests? Is their a design pattern that could help me with this? Should I be drawing state-machines in my code? I think this is a generic programing question, but if it makes any difference I'm using Django with MySQL.

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• Obtaining reference to Class instance by string name - VB.NET

  - by Jeff Williams

  Is it possible using Reflection or some other method to obtain a reference to a specific class instance from the name of that class instance? For example the framework for the applications i develop heavily uses public class instances such as: Public bMyreference as MyReference = new MyReference Then throughout the application bMyReference is used by custom controls and code. One of the properties of the custom controls is the "FieldName" which references a Property in these class instances (bMyReference.MyField) as a string. What i would like to be able to do is analyze this string "bMyReference.MyField" and then refer back to the actual Instance/Property. In VB6 I would use an EVAL or something simular to convert the string to an actual object but this obviously doesn't work in VB.net What I'm picturing is something like this Dim FieldName as String = MyControl.FieldName ' sets FielName to bMyReference.MyField Dim FieldObject() as String = FieldName.Split(".") ' Split into the Object / Property Dim myInstance as Object = ......... ' Obtain a reference to the Instance and set as myInstance Dim myProperty = myInstance.GetType().GetProperty(FieldObject(1))

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• formatting an array of mobile numbers

  - by Kyle Hudson

  Hi, I am creating a SMS app the following code is supposed to: check if the mobile/cell number is 11 characters long. check if the number starts with 07. If neither of these conditions are met, it should remove the number from the array. So the following numbers would be valid: 07123456789,07123456790,07123456791,07123456792,07123456793,07123456794 However the following wouldn't (and need to be removed): 0801458,07855488,6695522214124514 $param["number"] = "07123456789,07123456790,07123456791,07123456792,07123456793,07123456794,0801458,07855488,6695522214124514"; $number = explode(',', $param["number"]); foreach($number as $num){ if (!substr_compare($num, "07", 0, 3, false)) { unset($num); } elseif (substr_compare($num, "07", 0, 3, true)) { if(strlen($num) == 11) { $li .= "447" . substr($num, 2) . ','; } } } $il .= substr($li, 0, strlen($li)-1); echo $il; // $request = substr($request, 0, strlen($request)-1); // return $n; } I also need to remove the final comma from the result. Any help will be appriciated. Thanks, Kyle

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• jquery live and callbacks via wcf services

  - by vondip

  Hi all, I am writing a web app with asp.net, c# and jquery. Most of the time I'm writing dynamic html to the browser and using different web services to get the content needed. My call to the service: function WriteProducts(currentIndex, selectedCategoryId, callback) { var d = new Date(); MyAppServices.GetProducts(selectedCategoryId, currentIndex, 8, d.getTime().toString(), callback, function func() { alert('failure'); }); } The request usually gets translated to this (using firebug I monitored it): http://localhost:8080/MyApp/MyAppServices.svc/GetProducts?categoryId=0&fromIndex=0&toIndex=8&randomNumber=%221271800014441%22 The problem starts when part of the html controls dynamically rendered need to respond to click events. This is when I start using jquery's live method: $('.filter').live('click', function(event) { WriteProducts(0, selectedCategoryId, PopulateDivs); }); Now from some reason, the request passed to the server becomes this: http://localhost:8080/MyApp/MyAppServices.svc/GetProducts?categoryId=**%2217%22**&fromIndex=0&toIndex=8&randomNumber=%221271799783355%22 where did these %22 come from? If I take them out, the request passes successfully. I have no idea who inserted these %22, but they are causing havoc here! Guys, do you perhaps have a clue?

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• Render multiple Form instances

  - by vorpyg

  I have a simple application where users are supposed to bet on outcome of a match. A match consists of two teams, a result and a stake. Matches with teams are created in the Django admin, and participants are to fill in result and stake. The form must be generated dynamically, based on the matches in the database. My idea is to have one (Django) Form instance for each match and pass these instances to the template. It works fine when I do it from django shell, but the instances aren't rendered when I load my view. The form looks like this: class SuggestionForm(forms.Form): def __init__(self, *args, **kwargs): try: match = kwargs.pop('match') except KeyError: pass super(SuggestionForm, self).__init__(*args, **kwargs) label = match self.fields['result'] = forms.ChoiceField(label=label, required=True, choices=CHOICES, widget=forms.RadioSelect()) self.fields['stake'] = forms.IntegerField(label='', required=True, max_value=50, min_value=10, initial=10) My (preliminary) view looks like this: def suggestion_form(request): matches = Match.objects.all() form_collection = {} for match in matches: f = SuggestionForm(request.POST or None, match=match) form_collection['match_%s' % match.id] = f return render_to_response('app/suggestion_form.html', { 'forms': form_collection, }, context_instance = RequestContext(request) ) My initial thought was that I could pass the form_collection to the template and the loop throught the collection like this, but id does not work: {% for form in forms %} {% for field in form %} {{ field }} {% endfor %} {% endfor %} (The output is actually the dict keys with added spaces in between each letter - I've no idea why…) It works if I only pass one Form instance to the template and only runs the inner loop. Suggestions are greatly appreciated.

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• Retrieve values from multimdimensional array

  - by vincentlerry

  I have a great difficulty. I need to retrieve [title], [url] and [abstract] values ??from this multidimensional array. Also, I have to store those values in mysql database. thanks in advance!!! Array ( [bossresponse] = Array ( [responsecode] = 200 [limitedweb] = Array ( [start] = 0 [count] = 20 [totalresults] = 972000 [results] = Array ( [0] = Array ( [date] = [clickurl] = http://www.torchlake.com/ [url] = http://www.torchlake.com/ [dispurl] = www.torchlake.com [title] = Torch Lake, COLI Inc, Highspeed, Dial-up, Wireless ... [abstract] = Welcome to COLI Inc. Chain O' Lake Internet. Local Northern Michigan ISP, offering Dialup Internet access, Wireless access, Web design, and T1 services in Northern ... ) [1] = Array ( [date] = [clickurl] = http://en.wikipedia.org/wiki/Torch_Lake_(Antrim_County,_Michigan) [url] = http://en.wikipedia.org/wiki/Torch_Lake_(Antrim_County,_Michigan) [dispurl] = en.wikipedia.org/wiki/Torch_Lake_(Antrim_County,_Michigan) [title] = Torch Lake (Antrim County, Michigan) - Wikipedia, the free ... [abstract] = Torch Lake at 19 miles (31 km) long is Michigan's longest lake and at approximately 18,770 acres (76 km²) is Michigan's second largest lake. Within it are several ... ) this is the entire code that generates this array: require("OAuth.php"); $cc_key = ""; $cc_secret = ""; $url = "http://yboss.yahooapis.com/ysearch/limitedweb"; $args = array(); $args["q"] = "car"; $args["format"] = "json"; $args["count"] = 20; $consumer = new OAuthConsumer($cc_key, $cc_secret); $request = OAuthRequest::from_consumer_and_token($consumer, NULL,"GET", $url, $args); $request-sign_request(new OAuthSignatureMethod_HMAC_SHA1(), $consumer, NULL); $url = sprintf("%s?%s", $url, OAuthUtil::build_http_query($args)); $ch = curl_init(); $headers = array($request-to_header()); curl_setopt($ch, CURLOPT_HTTPHEADER, $headers); curl_setopt($ch, CURLOPT_URL, $url); curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE); $rsp = curl_exec($ch); $results = json_decode($rsp, true);

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• Delphi constants and references

  - by Sambatyon

  I want to pass constant references to functions in delphi, so I am sure that the referenced object won't change and to save time and memory. So I want to declare a function like function foo(var const Value : Bar) : Boolean; however this is not allowed. I thought constant values would be automatically sent as references. However I found out that it is not the case (getting the address of an object before sending it to the function gives me $12F50C and the address of the same object inside the function is $12F564) What can I do to send constant references?

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• JavaScript cookie value can't be retrieved in Django

  - by Boris Rusev

  I am trying to build a web site in both English and Bulgarian using the Django framework. My idea is the user should click on a button, the page will reload and the language will be changed. This is how I am trying to do it: In my html I hava a the button tag <button id='btn' onclick="changeLanguage();" type="button"> ... </button> An excerpt from cookies.js: function changeLanguage() { if (getCookie('language') == 'EN') { document.getElementById('btn').innerHTML = getCookie('language'); setCookie("language", 'BG'); } else { document.getElementById('btn').innerHTML = getCookie('language'); setCookie("language", 'EN'); } } function setCookie(sName, sValue, oExpires, sPath, sDomain, bSecure) { var sCookie = sName + "=" + encodeURIComponent(sValue); if (oExpires) { sCookie += "; expires=" + oExpires.toGMTString(); } if (sPath) { sCookie += "; path=" + sPath; } if (sDomain) { sCookie += "; domain=" + sDomain; } if (bSecure) { sCookie += "; secure"; } document.cookie = sCookie; } And in my views.py file this is the situation @base def index(request): if request.session['language'] == 'EN': return """<b>%s</b>""" % "Home" else request.session['language'] == 'BG': return """<b>%s</b>""" % "??????" So I know that my JS changes the value of the language cookie but I think Django doesn't get that. On the other hand when I set and get the cookie in my Python code again the cookie is set. My question is whether there is a way to make JS and Django work together - JavaScript sets the cookie value and Python only reads it when asked and takes adequate actions? Thank you.

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• Mamimum page fetch with maximum bandwith

  - by Ehsan

  Hi I want to create an application like a spider I've implement fetching page as the following code in multi-thread application but there is two problem 1) I want to use my maximum bandwidth to send/receive request, how should I config my request to do so (Like Download Accelerator application and the like) cause I heard the normal application will use 66% of the available bandwidth. 2) I don't know what exactly HttpWebRequest.KeepAlive do, but as its name implies I think i can create a connection to a website and without closing the connection sending another request to that web site using existing connection. does it boost performance or Im wrong public PageFetchResult Fetch() { PageFetchResult fetchResult = new PageFetchResult(); try { HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(URLAddress); HttpWebResponse resp = (HttpWebResponse)req.GetResponse(); Uri requestedURI = new Uri(URLAddress); Uri responseURI = resp.ResponseUri; if (Uri.Equals(requestedURI, responseURI)) { string resultHTML = ""; byte[] reqHTML = ResponseAsBytes(resp); if (!string.IsNullOrEmpty(FetchingEncoding)) resultHTML = Encoding.GetEncoding(FetchingEncoding).GetString(reqHTML); else if (!string.IsNullOrEmpty(resp.CharacterSet)) resultHTML = Encoding.GetEncoding(resp.CharacterSet).GetString(reqHTML); req.Abort(); resp.Close(); fetchResult.IsOK = true; fetchResult.ResultHTML = resultHTML; } else { URLAddress = responseURI.AbsoluteUri; relayPageCount++; if (relayPageCount > 5) { fetchResult.IsOK = false; fetchResult.ErrorMessage = "Maximum page redirection occured."; relayPageCount = 0; return fetchResult; } req.Abort(); resp.Close(); return Fetch(); } } catch (Exception ex) { fetchResult.IsOK = false; fetchResult.ErrorMessage = ex.Message; } return fetchResult; }

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• Testing a (big) collection retrieved from a db

  - by Bas

  I'm currently doing integration testing on a live database and I have the following sql statement: var date = DateTime.Parse("01-01-2010 20:30:00"); var result = datacontext.Repository<IObject>().Where(r => r.DateTime > date).First(); Assert.IsFalse(result.Finished); I need to test if the results retrieved from the statement, where the given date is less then the date of the object, have Finished set to False. I do not know how many results I get back and currently I'm getting the first object of the list and check if that object has Finished set to false. I know testing only the first item of the list is not valid testing, as a solution for that I could iterate through the list and check all items on Finished, but putting logic in a Test is kinda going against the concept of writing 'good' tests. So my question is: Does anyone have a good solution of how to properly test the results of this list?

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• ASP.NET MVC Generic Controllers and Spring.NET

  - by Jason

  Hello, I am creating an application using ASP.NET MVC (2) and Spring.NET. Since most of my Controller implementations just implement the similar CRUD operations, I would like to just create a single Generic controller, as explained here: http://stackoverflow.com/questions/848904/in-asp-net-mvc-is-it-possible-to-make-a-generic-controller However, the above example doesn't take DI frameworks into consideration. What I'm thinking is to create this (warning: this is an ugly mass of code I need help with): public SpringGenericControllerFactory : DefaultControllerFactory { public IController CreateController(RequestContext requestContext, string controllerName) { // Determine the controller type to return Type controllerType = Type.GetType("MyController").MakeGenericType(Type.GetType(controllerName)); // Return the controller return Activator.CreateInstance(controllerType) as IController; } } The entries in objects.xml would look something like this: <object id="controllerFactory" type="Application.Controllers.SpringGenericControllerFactory" /> <object id="DepartmentController" factory-method="CreateController" factory-object="controllerFactory" /> Can anyone pick through this and offer advice?

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• MVC JsonResult not working with chrome?

  - by Karsten Detmold

  i want jquery to take a JsonResult from my MVC controller but it does'nt receive any data! If I put the output into a textfile and enter its link its working so I think my jQuery is fine. Then I was testing with other browsers like chrome and I saw NOTHING. The requested page was just emtpy.. no errors. Also IE seems to have problems receiving my string.. only firefox displays the string but why? public JsonResult jsonLastRequests() { List<Request> requests = new List<Request>(); while (r.Read()) { requests.Add(new Models.Request() { ID = (int)r[0], SiteID = r[1].ToString(), Lat = r[2].ToString(), City = r[4].ToString(), CreationTime = (DateTime)r[5] }); } r.Close(); return Json(requests); } I found out that also if I want to return the JSON as string its not working! Its working with a string in all browsers now.. but jQuery is still not loading anything var url = "http://../jsonLastRequests"; var source = { datatype: "json", datafields: [ { name: 'ID' }, { name: 'SiteID' }, { name: 'Lat' }, { name: 'CreationTime' }, { name: 'City' }, ], id: 'id', url: url }; var dataAdapter = new $.jqx.dataAdapter(source, { downloadComplete: function (data, status, xhr) { }, loadComplete: function (data) { }, loadError: function (xhr, status, error) { } }); I fixed my problem by adding: access-control-allow-origin:*

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• Assigning a material in Blender with a script

  - by Narcolapser

  Question: How do you assign a material with a script to an object in blender? Info: I have this script to import a proprietary model type of mine that is basically a star map with object consisting of a single vertex. in order to make them look like stars and be visible they are all going to have a halo material assigned to them. I'm figuring out how to make this material and give it the values just fine, but I can't seem to get it to assign. I tried the most obvious thing which was: objectName.setMaterial(materialName) but that did nothing. and when i would take an object that had a material and call the getMaterial function on it, it would return nothing. there is something I'm missing here, can some one shed some light on it? Thanks. ~TA

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• Using PHP to get the source code of a URL I must be logged in to reach

  - by Maxwell

  I am trying to write a PHP script that will get the source code of a page in my Amazon account. However, to reach that page, I must be logged in. From what I understand, I should be able to accomplish this by posting the correct request headers, and then capturing the HTML response. Is that correct? If so, I'd really appreciate it if someone could explain to me how exactly I would do this. If it's not right, I'd love to hear the correct way of doing it! I've used Firebug to get the request and response headers I need. It's just a matter of what to do with them now. I read elsewhere on this site that you can't send a request with the PHP post method, and that perhaps using cURL is the way to go. I really know nothing about cURL, so the more info the better. Also, feel free to point me to some useful tutorials on this topic. Thanks! Max

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• errors with gae-sessions and nose

  - by Kekito

  I'm running into a few problems with adding gae-sessions to a relatively mature GAE app. I followed the readme carefully and also looked at the demo. First, just adding the gaesesions directory to my app causes the following error when running tests with nose and nose-gae: Exception ImportError: 'No module named threading' in <bound method local.__del__ of <_threading_local.local object at 0x103e10628>> ignored All the tests run fine so not a big problem but suggests that something isn't right. Next, if I add the following two lines of code: from gaesessions import get_current_session session = get_current_session() I get the following error: Traceback (most recent call last): File "/Users/.../unit_tests.py", line 1421, in testParseFBRequest data = tasks.parse_fb_request(sr) File "/Users/.../tasks.py", line 220, in parse_fb_request session = get_current_session() File "/Users/.../gaesessions/__init__.py", line 36, in get_current_session return _tls.current_session File "/Library/.../python2.7/_threading_local.py", line 193, in __getattribute__ return object.__getattribute__(self, name) AttributeError: 'local' object has no attribute 'current_session' Any suggestions on fixing the above would be greatly appreciated.

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• Communication between (Desktop/Smartphone) Application and Web Application

  - by erlord

  Hi all I wonder what is the commonly used method and protocol for a, say, smartphone application to send its data to a web application (where these data should be proceeded and stored). My naive beginner's approach would be something like this: From my smartphone app, use a framework encoding my data object into a json object Send this object via http to a listener addressed by a dedicated URL On the server side, use a JSON parser and store it via ORM etc. into a database Questions: Is this too naive? 2a. If yes: What is the appropiate way to tackle this workflow? 2b. If no: What frameworks to use in JAVA for serializing/deserializing to/from JSON objects? Any example for a json listener in the web? Tutorial for a http-protocol based Java listener? Thanks for all answers and suggestions in advance. Regs Me

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• SQL Get Latest Unique Rows

  - by Simpleton

  I have a log table, each row representing an object logging its state. Each object has a unique, unchanging GUID. There are multiple objects logging their states, so there will be thousands of entries, with objects continually inserting new logs. Everytime an object checks in, it is via an INSERT. I have the PrimaryKey, GUID, ObjectState, and LogDate columns in tblObjects. I want to select the latest (by datetime) log entry for each unique GUID from tblObjects, in effect a 'snapshot' of all the objects. How can this be accomplished?

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• Faster way to clone.

  - by AngryHacker

  I am trying to optimize a piece of code that clones an object: #region ICloneable public object Clone() { MemoryStream buffer = new MemoryStream(); BinaryFormatter formatter = new BinaryFormatter(); formatter.Serialize(buffer, this); // takes 3.2 seconds buffer.Position = 0; return formatter.Deserialize(buffer); // takes 2.1 seconds } #endregion Pretty standard stuff. The problem is that the object is pretty beefy and it takes 5.4 seconds (according ANTS Profiler - I am sure there is the profiler overhead, but still). Is there a better and faster way to clone?

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• jQuery-UI How-to stop realoding the tabs

  - by user256034

  I'm using jQuery UI tabs functionality to load tab content via Ajax. But I need to load the tabs only once. At the first request. <div id="tabContainer"> <ul> <li><a href="/Home/Tab1">Tab1</a></li> <li><a href="/Home/Tab2">Tab2</a></li> <li><a href="/Home/Tab3">Tab3</a></li> </ul> </div> I hooked up the select event. I'm able to see if the content is already loaded or not.But I'm missng the point how to stop jQuery from sending the request. $("#tabs").tabs({ select: function(event, ui) { if (ui.panel.innerHTML != '') { //What to do here to stop jQuery from sending the request. return; } } });

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• JS function returning another function

  - by Michael

  I want to understand about variables, that has been used in returning function. This is example code Prototype = {} Prototype.F = { bind: function() { var args = arguments, __method = args.shift(), object = args.shift(); return function() { return __method.apply(object, args.concat(arguments)); } } } function ObjectA() { ... this.addListener = Prototype.F.bind(this.eventSource.addListener, this.eventSource); ... } var a = ObjectA(); a.addListener(this); // assuming 'this' here will point to some window object As I understand the returning function in F() is not evaluated until it's called in the last line. It's ok to accept. So addListener will hold a function body containing 'apply'. But what I don't understand, when addListener is called, what kind of parameters it is going to have? particularly _method and args will always be uninitialized?

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• How can I intercept an exception occurred during serialization in WCF?

  - by bonomo

  I have a legit data object with all data contract / data member attributes. For some reason the WCF service crashes after the operation has completed and the result is passed as a return value. I believe it has something to do with WCF not being able to serialize that result properly. The test client doesn't say anything specific: The underlying connection was closed: The connection was closed unexpectedly. Server stack trace: at System.ServiceModel.Channels.HttpChannelUtilities.ProcessGetResponseWebException(WebException webException, HttpWebRequest request, HttpAbortReason abortReason) at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan timeout) at System.ServiceModel.Channels.RequestChannel.Request(Message message, TimeSpan timeout) at System.ServiceModel.Dispatcher.RequestChannelBinder.Request(Message message, TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout) at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation) at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message) Exception rethrown at [0]: at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type) at IFacade.PickSecurities(String pattern, Int32 atMost) at FacadeClient.PickSecurities(String pattern, Int32 atMost) Inner Exception: The underlying connection was closed: The connection was closed unexpectedly. at System.Net.HttpWebRequest.GetResponse() at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelRequest.WaitForReply(TimeSpan timeout) I am in control of creating the instance of the service using a customized service host factory. I know I can set up trace listeners and check the logs, but it's a lot of hassle to do. So I would rather handle it explicitly on the server at the time it happens. So I how can I intercept that exception programmatically and return an appropriate fault meassage?

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• Form Inheritance in Visual Studios designer implementations

  - by CooPzZ

  I'm in the process of Moving a project from Visual Studio 2003 to 2005 and have just seen the The event Click is read-only and cannot be changed when using inherited forms regardless of the Modifier on the Base Forms Controls will make all the Controls from the Base Readonly in the designer (Though in 2003 it didn't work this way). I found this post metioning that this functionality has been temporarily" disabled http://social.msdn.microsoft.com/Forums/en-US/winformsdesigner/thread/c25cec28-67a5-4e30-bb2d-9f8dbd41eb3a Can anyone confirm whether this feature is used anymore? or how to program around it to be able to use the Base Control Events and still have a designer? This is one way I've found but quite painfull when it used to do the plumbing for you. even just hiding one of the controls you have manually do now. Public Class BFormChild Friend Overrides Sub cmdApply_Click(ByVal sender As Object, ByVal e As System.EventArgs) MyBase.cmdApply_Click(sender, e) End Sub Friend Overrides Sub cmdCancel_Click(ByVal sender As Object, ByVal e As System.EventArgs) MyBase.cmdCancel_Click(sender, e) End Sub Friend Overrides Sub cmdOk_Click(ByVal sender As Object, ByVal e As System.EventArgs) MyBase.cmdOk_Click(sender, e) End Sub End Class

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• How to handle failure to release a resource which is contained in a smart pointer?

  - by cj

  How should an error during resource deallocation be handled, when the object representing the resource is contained in a shared pointer? Smart pointers are a useful tool to manage resources safely. Examples of such resources are memory, disk files, database connections, or network connections. // open a connection to the local HTTP port boost::shared_ptr<Socket> socket = Socket::connect("localhost:80"); In a typical scenario, the class encapsulating the resource should be noncopyable and polymorphic. A good way to support this is to provide a factory method returning a shared pointer, and declare all constructors non-public. The shared pointers can now be copied from and assigned to freely. The object is automatically destroyed when no reference to it remains, and the destructor then releases the resource. /** A TCP/IP connection. */ class Socket { public: static boost::shared_ptr<Socket> connect(const std::string& address); virtual ~Socket(); protected: Socket(const std::string& address); private: // not implemented Socket(const Socket&); Socket& operator=(const Socket&); }; But there is a problem with this approach. The destructor must not throw, so a failure to release the resource will remain undetected. A common way out of this problem is to add a public method to release the resource. class Socket { public: virtual void close(); // may throw // ... }; Unfortunately, this approach introduces another problem: Our objects may now contain resources which have already been released. This complicates the implementation of the resource class. Even worse, it makes it possible for clients of the class to use it incorrectly. The following example may seem far-fetched, but it is a common pitfall in multi-threaded code. socket->close(); // ... size_t nread = socket->read(&buffer[0], buffer.size()); // wrong use! Either we ensure that the resource is not released before the object is destroyed, thereby losing any way to deal with a failed resource deallocation. Or we provide a way to release the resource explicitly during the object's lifetime, thereby making it possible to use the resource class incorrectly. There is a way out of this dilemma. But the solution involves using a modified shared pointer class. These modifications are likely to be controversial. Typical shared pointer implementations, such as boost::shared_ptr, require that no exception be thrown when their object's destructor is called. Generally, no destructor should ever throw, so this is a reasonable requirement. These implementations also allow a custom deleter function to be specified, which is called in lieu of the destructor when no reference to the object remains. The no-throw requirement is extended to this custom deleter function. The rationale for this requirement is clear: The shared pointer's destructor must not throw. If the deleter function does not throw, nor will the shared pointer's destructor. However, the same holds for other member functions of the shared pointer which lead to resource deallocation, e.g. reset(): If resource deallocation fails, no exception can be thrown. The solution proposed here is to allow custom deleter functions to throw. This means that the modified shared pointer's destructor must catch exceptions thrown by the deleter function. On the other hand, member functions other than the destructor, e.g. reset(), shall not catch exceptions of the deleter function (and their implementation becomes somewhat more complicated). Here is the original example, using a throwing deleter function: /** A TCP/IP connection. */ class Socket { public: static SharedPtr<Socket> connect(const std::string& address); protected: Socket(const std::string& address); virtual Socket() { } private: struct Deleter; // not implemented Socket(const Socket&); Socket& operator=(const Socket&); }; struct Socket::Deleter { void operator()(Socket* socket) { // Close the connection. If an error occurs, delete the socket // and throw an exception. delete socket; } }; SharedPtr<Socket> Socket::connect(const std::string& address) { return SharedPtr<Socket>(new Socket(address), Deleter()); } We can now use reset() to free the resource explicitly. If there is still a reference to the resource in another thread or another part of the program, calling reset() will only decrement the reference count. If this is the last reference to the resource, the resource is released. If resource deallocation fails, an exception is thrown. SharedPtr<Socket> socket = Socket::connect("localhost:80"); // ... socket.reset();

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• In Javascript, by what mechanism does setting an Image src property trigger an image load?

  - by brainjam

  One of the things you learn early on when manipulating a DOM using Javascript is the following pattern: var img = new Image(); // Create new Image object img.onload = function(){ // execute drawImage statements here } img.src = 'myImage.png'; // Set source path As far as I know, in general when you set an object property there are no side effects. So what is the mechanism for triggering an image load? Is it just magic? Or can I use a similar mechanism to implement a class Foo that supports a parallel pattern? var foo = new Foo(); // Create new object foo.barchanged = function(){ // execute something after side effect has completed } foo.bar = 'whatever'; // Assign something to 'bar' property I'm vaguely aware of Javascript getters and setters. Is this how Image.src triggers a load?

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• How to use Java on Google App Engine without exceeding minute quotas?

  - by Geo

  A very simple java code inside a doGet() servlet is getting more than a second of cpu time on GAE. I have read some quota related documentation and apparently I am not doing anything wrong. //Request the user Agent info String userAgent = req.getHeader("User-Agent"); I wanted to know what was using the CPU the most, I use a google help recommendation. //The two lines below will get the CPU before requesting User-Agent Information QuotaService qs = QuotaServiceFactory.getQuotaService(); long start = qs.getCpuTimeInMegaCycles(); //Request the user Agent info String userAgent = req.getHeader("User-Agent"); //The three lines below will get the CPU after requesting User-Agent Information // and informed it to the application log. long end = qs.getCpuTimeInMegaCycles(); double cpuSeconds = qs.convertMegacyclesToCpuSeconds(end - start); log.warning("CPU Seconds on geting User Agent: " + cpuSeconds); The only thing that the code above tells me is that inspecting the header will use more than a second (1000ms) of cpu time, which for Google is a warning on the log panel. That seems to be a very simple request and still is using more than a second of cpu. What I am missing?

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