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• Unity doesn't work

  - by Budda

  Yesterday I've implemented the code: CustomerProductManager productsManager = container.Resolve<CustomerProductManager>(); It was compilable and working. Today (probably I've modified something I am constantly getting the error: The non-generic method 'Microsoft.Practices.Unity.IUnityContainer.Resolve(System.Type, string, params Microsoft.Practices.Unity.ResolverOverride[])' cannot be used with type arguments My collegue has the same source code and doesn't have same error. Why? How to resolve the problem? P.S. line "using Microsoft.Practices.Unity;" is present in usings section. I've tried to replace generic version with non-generic one: CustomerProductManager productsManager = (CustomerProductManager)container.Resolve(typeof(CustomerProductManager)); And got another error: No overload for method 'Resolve' takes '1' arguments It seems like one of the assemblies is not referenced.. but which one? I have 2 of them referenced: 1. Microsoft.Practices.Unity.dll 2. Microsoft.Practices.ServiceLocation.dll P.P.S. I've saw similar problem http://unity.codeplex.com/WorkItem/View.aspx?WorkItemId=8205 but it is resolved as "not a bug" Any thought will be helpful

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• Logging in worker threads spawned from a pylons application does not seem to work

  - by TimM

  I have a pylons application where, under certain cirumstances I want to spawn multiple worker threads to process items in a queue. Right now we aren't making use of a ThreadPool (would be ideal, but we'll add that in later). The main problem is that the worker threads logging does not get written to the log files. When I run the code outside of the pylons application the logging works fine. So I think its something to do with the pylons log handler but not sure what. Here is a basic example of the code (trimmed down): import logging log = logging.getLogger(__name__) import sys from Queue import Queue from threading import Thread, activeCount def run(input, worker, args = None, simulteneousWorkerLimit = None): queue = Queue() threads = [] if args is not None: if len(args) > 0: args = list(args) args = [worker, queue] + args args = tuple(args) else: args = (worker, queue) # start threads for i in range(4): t = Thread(target = __thread, args = args) t.daemon = True t.start() threads.append(t) # add ThreadTermSignal inputData = list(input) inputData.extend([ThreadTermSignal] * 4) # put in the queue for data in inputData: queue.put(data) # block until all contents are downloaded queue.join() log.critical("** A log line that appears fine **") del queue for thread in threads: del thread del threads class ThreadTermSignal(object): pass def __thread(worker, queue, *args): try: while True: data = queue.get() if data is ThreadTermSignal: sys.exit() try: log.critical("** I don't appear when run under pylons **") finally: queue.task_done() except SystemExit: queue.task_done() pass Take note, that the log lin within the RUN method will show up in the log files, but the log line within the worker method (which is run in a spawned thread), does not appear. Any help would be appreciated. Thanks ** EDIT: I should mention that I tried passing in the "log" variable to the worker thread as well as redefining a new "log" variable within the thread and neither worked. ** EDIT: Adding the configuration used for the pylons application (which comes out of the INI file). So the snippet below is from the INI file. [loggers] keys = root [handlers] keys = wsgierrors [formatters] keys = generic [logger_root] level = WARNING handlers = wsgierrors [handler_console] class = StreamHandler args = (sys.stderr,) level = WARNING formatter = generic [handler_wsgierrors] class = pylons.log.WSGIErrorsHandler args = () level = WARNING format = generic

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• Uploadify not working with ASP.NET WebForms

  - by João Guilherme

  Hi ! I'm trying to use Uploadify in a ASP.NET webforms project. The problem is that my script is not calling the generic handler. Here is the script. <input id="fileInput" name="fileInput" type="file" /> <script type="text/javascript"> $(document).ready(function() { $('#fileInput').uploadify({ 'uploader': '/Ferramenta/Comum/Uploadify/uploadify.swf', 'script': 'UploadTest.ashx', 'cancelImg': '/Ferramenta/Comum/Uploadify/cancel.png', 'folder': "/Ferramenta/Geral/", 'auto': true, 'onError': function(event, queueID, fileObj, errorObj) { alert('error'); }, 'onComplete': function(event, queueID, fileObj, response, data) { alert('complete'); }, 'buttonText' : 'Buscar Arquivos' }); }); </script> This is the code of the generic handler (just to test) using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.Services; using System.IO; namespace Tree.Ferramenta.Geral { public class UploadTest : IHttpHandler { public void ProcessRequest(HttpContext context) { context.Response.Write("1"); } public bool IsReusable { get { return false; } } } } Any ideas ? Thanks !

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• Cannot resolve Dictionary in Unity container

  - by IanR

  Hi, I've just stumbled upon this: within a Unity container, I want to register IDictionary<TK, TV>; assume that it's IDictionary<string, int> _unityContainer = new UnityContainer() .RegisterType<IDictionary<string, int>, Dictionary<string, int>>(); but if I try var d = _unityContainer.Resolve<IDictionary<string, int>>(); it fails to resolve... I get... Microsoft.Practices.Unity.ResolutionFailedException: Microsoft.Practices.Unity.ResolutionFailedException: Resolution of the dependency failed, type = "System.Collections.Generic.IDictionary`2[System.String,System.Int32]", name = "(none)". Exception occurred while: while resolving. Exception is: InvalidOperationException - The type Dictionary`2 has multiple constructors of length 2. Unable to disambiguate. At the time of the exception, the container was: Resolving System.Collections.Generic.Dictionary2[System.String,System.Int32],(none) (mapped from System.Collections.Generic.IDictionary2[System.String,System.Int32], (none)) --- System.InvalidOperationException: The type Dictionary`2 has multiple constructors of length 2. Unable to disambiguate.. So it looks like it has found the Type to resolve (being Dictionary<string, int>) but failed to new it up... How come unity can't resolve this type? If I type IDictionary<string, int> d = new Dictionary<string, int>() that works... any ideas? thanks!

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• How can I use Convert.ChangeType to convert string into numerics with group separator?

  - by Loic

  Hello, I want to make a generic string to numeric converter, and provide it as a string extension, so I wrote the following code: public static bool TryParse<T>( this string text, out T result, IFormatProvider formatProvider ) where T : struct try { result = (T)Convert.ChangeType( text, typeof( T ), formatProvider ); return true; } catch(... I call it like this: int value; var ok = "123".TryParse(out value, NumberFormatInfo.CurrentInfo) It works fine until I want to use a group separator: As I live in France, where the thousand separator is a space and the decimal separator is a comma, the string "1 234 567,89" should be equals to 1234567.89 (in Invariant culture). But, the function crashes! When a try to perform a non generic conversion, like double.Parse(...), I can use an overload which accepts a NumberStyles parameter. I specify NumberStyles.Number and this time it works! So, the questions are : Why the parsing does not respect my NumberFormatInfo (where the NumberGroupSeparator is well specified to a space, as I specified in my OS) How could I make work the generic version with Convert.ChangeTime, as it has no overload wich accepts a NumberStyles parameter ?

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• Java Generics: Dealing with an intermediate unknown type

  - by Matt

  I am trying to figure out a way to deal with a particular problem in a type safe manner, or to put it more specifically without any explicit casts. I have a class that takes in a generic request and returns a generic response like such: public class RetrievalProcessor<Req extends Request, Resp> implements RequestProcessor<Req, Resp>{ private Dao<Req> dao; private RawResponseTransformer<Resp> transformer; @Override public Resp process(Req request) { return transformer.transformResponse(dao.retrieveRawResponse(request)); } } My problem is the following. My Dao object can be many different things REST, JDBC, some other proprietary object. I can't be certain of the type of object that the Dao will return. I do know the type of object my caller would like and that is the Resp type on the generic, and the job of the RawResponseTransformer is to transform that Dao response into something that the caller can consume. The problem I have is I can't figure out a way that feels clean to do that. I have considered putting the intermediate type as part of the definition of the class, but it doesn't seem like the caller should know, or really care, what the intermediate form is. Hoping someone might have a good clean idea for handling this.

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• Possible to create an implicit cast for an anonymous type to a dictionary?

  - by Ralph

  I wrote a method like this: using AttrDict = System.Collections.Generic.Dictionary<string, object>; using IAttrDict = System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, object>>; static string HtmlTag(string tagName, string content = null, IAttrDict attrs = null) { var sb = new StringBuilder("<"); sb.Append(tagName); if(attrs != null) foreach (var attr in attrs) sb.AppendFormat(" {0}=\"{1}\"", attr.Key, attr.Value.ToString().EscapeQuotes()); if (content != null) sb.AppendFormat(">{0}</{1}>", content, tagName); else sb.Append(" />"); return sb.ToString(); } Which you can call like HtmlTag("div", "hello world", new AttrDict{{"class","green"}}); Not too bad. But what if I wanted to allow users to pass an anonymous type in place of the dict? Like HtmlTag("div", "hello world", new {@class="green"}); Even better! I could write the overload easily, but the problem is I'm going to have about 50 functions like this, I don't want to overload each one of them. I was hoping I could just write an implicit cast to do the work for me... public class AttrDict : Dictionary<string, object> { public static implicit operator AttrDict(object obj) { // conversion from anonymous type to AttrDict here } } But C# simply won't allow it: user-defined conversions to or from a base class are not allowed So what can I do?

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• What was Tim Sweeney thinking? (How does this C++ parser work?)

  - by Frank Krueger

  Tim Sweeney of Epic MegaGames is the lead developer for Unreal and a programming language geek. Many years ago posted the following screen shot to VoodooExtreme: As a C++ programmer and Sweeney fan, I was captivated by this. It shows generic C++ code that implements some kind of scripting language where that language itself seems to be generic in the sense that it can define its own grammar. Mr. Sweeney never explained himself. :-) It's rare to see this level of template programming, but you do see it from time to time when people want to push the compiler to generate great code or because they want to create generic code (for example, Modern C++ Design). Tim seems to be using it to create a grammar in Parser.cpp - you can see what look like prioritized binary operators. If that is the case, then why does Test.ae look like it's also defining a grammar? Obviously this is a puzzle that needs to be solved. Victory goes to the answer with a working version of this code, or the most plausible explanation, or to Tim Sweeney himself if he posts an answer. :-)

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• Print raw data to a thermal-printer using .NET

  - by blauesocke

  I'm trying to print out raw ascii data to a thermal printer. I do this by using this code example: http://support.microsoft.com/kb/322091 but my printer prints always only one character and this not until I press the form feed button. If I print something with notepad the printer will do a form feed automatically but without printing any text. The printer is connected via usb over a lpt2usb adapter and Windows 7 uses the "Generic - Generic / Text Only" driver. Anyone knows what is going wrong? How is it possible to print some words and do some form feeds? Are there some control characters I have to send? And if yes: How do I send them? Edit 14.04.2010 21:51 My code (C#) looks like this: PrinterSettings s = new PrinterSettings(); s.PrinterName = "Generic / Text Only"; RawPrinterHelper.SendStringToPrinter(s.PrinterName, "Test"); This code will return a "T" after I pressed the form feed button (This litte black button here: swissmania.ch/images/935-151.jpg - sorry, not enough reputation for two hyperlinks) Edit 15.04.2010 16:56 I'm using now the code form here: c-sharpcorner.com/UploadFile/johnodonell/PrintingDirectlytothePrinter11222005001207AM/PrintingDirectlytothePrinter.aspx I modified it a bit that I can use the following code: byte[] toSend; // 10 = line feed // 13 carriage return/form feed toSend = new byte[1] { 13 }; PrintDirect.WritePrinter(lhPrinter, toSend, toSend.Length, ref pcWritten); Running this code has the same effekt like pressing the form feed button, it works fine! But code like this still does not work: byte[] toSend; // 10 = line feed // 13 carriage return/form feed toSend = new byte[2] { 66, 67 }; PrintDirect.WritePrinter(lhPrinter, toSend, toSend.Length, ref pcWritten); This will print out just a "B" but I expect "BC" and after running any code I have to reconnect the USB cable to make it work agian. Any ideas?

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• How can I write reusable Javascript?

  - by RenderIn

  I've started to wrap my functions inside of Objects, e.g.: var Search = { carSearch: function(color) { }, peopleSearch: function(name) { }, ... } This helps a lot with readability, but I continue to have issues with reusabilty. To be more specific, the difficulty is in two areas: Receiving parameters. A lot of times I will have a search screen with multiple input fields and a button that calls the javascript search function. I have to either put a bunch of code in the onclick of the button to retrieve and then martial the values from the input fields into the function call, or I have to hardcode the HTML input field names/IDs so that I can subsequently retrieve them with Javascript. The solution I've settled on for this is to pass the field names/IDs into the function, which it then uses to retrieve the values from the input fields. This is simple but really seems improper. Returning values. The effect of most Javascript calls tends to be one in which some visual on the screen changes directly, or as a result of another action performed in the call. Reusability is toast when I put these screen-altering effects at the end of a function. For example, after a search is completed I need to display the results on the screen. How do others handle these issues? Putting my thinking cap on leads me to believe that I need to have an page-specific layer of Javascript between each use in my application and the generic methods I create which are to be used application-wide. Using the previous example, I would have a search button whose onclick calls a myPageSpecificSearchFunction, in which the search field IDs/names are hardcoded, which marshals the parameters and calls the generic search function. The generic function would return data/objects/variables only, and would not directly read from or make any changes to the DOM. The page-specific search function would then receive this data back and alter the DOM appropriately. Am I on the right path or is there a better pattern to handle the reuse of Javascript objects/methods?

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• How to make Stack.Pop threadsafe

  - by user260197

  I am using the BlockingQueue code posted in this question, but realized I needed to use a Stack instead of a Queue given how my program runs. I converted it to use a Stack and renamed the class as needed. For performance I removed locking in Push, since my producer code is single threaded. My problem is how can thread working on the (now) thread safe Stack know when it is empty. Even if I add another thread safe wrapper around Count that locks on the underlying collection like Push and Pop do, I still run into the race condition that access Count and then Pop are not atomic. Possible solutions as I see them (which is preferred and am I missing any that would work better?): Consumer threads catch the InvalidOperationException thrown by Pop(). Pop() return a nullptr when _stack-Count == 0, however C++-CLI does not have the default() operator ala C#. Pop() returns a boolean and uses an output parameter to return the popped element. Here is the code I am using right now: generic <typename T> public ref class ThreadSafeStack { public: ThreadSafeStack() { _stack = gcnew Collections::Generic::Stack<T>(); } public: void Push(T element) { _stack->Push(element); } T Pop(void) { System::Threading::Monitor::Enter(_stack); try { return _stack->Pop(); } finally { System::Threading::Monitor::Exit(_stack); } } public: property int Count { int get(void) { System::Threading::Monitor::Enter(_stack); try { return _stack->Count; } finally { System::Threading::Monitor::Exit(_stack); } } } private: Collections::Generic::Stack<T> ^_stack; };

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• Moq a function with 5+ parameters and access invocation arguments.

  - by beerncircus

  I have a function I want to Moq. The problem is that it takes 5 parameters. The framework only contains Action<T1,T2,T3,T4> and Moq's generic CallBack() only overloads Action and the four generic versions. Is there an elegant workaround for this? This is what I want to do: public class Filter : IFilter { public int Filter(int i1, int i2, int i3, int i4, int i5){return 0;} } //Moq code: var mocker = new Mock<IFilter>(); mocker.Setup(x => x.Filter( It.IsAny<int>(), It.IsAny<int>(), It.IsAny<int>(), It.IsAny<int>(), It.IsAny<int>(), It.IsAny<int>()) .Callback ( (int i1, int i2, int i3, int i4, int i5) => i1 * 2 ); Moq doesn't allow this because there is no generic Action that takes 5+ parameters. I've resorted to making my own stub. Obviously, it would be better to use Moq with all of its verifications, etc.

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• How to print the address an ada access variable points to?

  - by georg

  I want to print the address of an access variable (pointer) for debugging purposes. type Node is private; type Node_Ptr is access Node; procedure foo(n: in out Node_Ptr) is package Address_Node is new System.Address_To_Access_Conversions(Node); use Address_Node; begin Put_Line("node at address " & System.Address_Image(To_Address(n))); end foo; Address_Image returns the string representation of an address. System.Address_To_Access_Conversions is a generic package to convert between addresses and access types (see ARM 13.7.2), defined as follows: generic type Object(<>) is limited private; package System.Address_To_Access_Conversions is -- [...] type Object_Pointer is access all Object; -- [...] function To_Address(Value : Object_Pointer) return Address; -- [...] end System.Address_To_Access_Conversions; gnat gives me the following errors for procedure foo defined above: expected type "System.Address_To_Access_Conversions.Object_Pointer" from instance at line... found type "Node_Ptr" defined at ... Object_Pointer ist definied as access all Object. From my understanding the type Object is Node, therefore Object_Ptr is access all Node. What is gnat complaining about? I guess my understanding of Ada generics is flawed and I am not using System.Address_To_Access_Conversions correctly. EDIT: I compiled my code with "gnatmake -gnatG" to see the generic instantiation: package address_node is subtype btree__clear__address_node__object__2 is btree__node; type btree__clear__address_node__object_pointer__2 is access all btree__clear__address_node__object__2; function to_address (value : btree__clear__address_node__object_pointer__2) return system__address; end address_node; btree__node is the mangled name of the type Node as defined above, so I really think the parameter type for to_address() is correct, yet gnat is complaining (see above).

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• “Could not find type” error loading a form in the Designer

  - by Vaccano

  This is the exact same question as this one: “Could not find type” error loading a form in the Designer Before anyone goes closing my question please read that one. You will realize that it did not get a real answer. I hope to get a full answer (rather than a workaround) from this question. When I create a class that descends from Control and uses generics, that class fails to load in the designer. Here is and example: class OwnerDrawnListBox<T> : System.Windows.Forms.Control { private readonly List<T> _items; // Other list box private stuff here public OwnerDrawnListBox() { _items = new List<T>(); } // More List box code } I then use this in my designer: private OwnerDrawnListBox<Bag> lstAvailable; private void InitializeComponent() { // Used to be System.Windows.Forms.ListBox(); this.lstAvailable = new ARUP.ScanTrack.Mobile.OwnerDrawnListBox<Bag>(); // Other items } If the generic class is subclassed (to a non-generic) then the referenced question says that it works fine (ie if I made Class BagOwnerDrawListBox: OwnerDrawnListBox<Bag>). What I want to know is there a way to "fix" this so that the generic item is accepted by the designer? Side Note: I am using the Compact Framework.

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• How to disable mod_security2 rule (false positive) for one domain on centos 5

  - by nicholas.alipaz

  Hi I have mod_security enabled on a centos5 server and one of the rules is keeping a user from posting some text on a form. The text is legitimate but it has the words 'create' and an html <table> tag later in it so it is causing a false positive. The error I am receiving is below: [Sun Apr 25 20:36:53 2010] [error] [client 76.171.171.xxx] ModSecurity: Access denied with code 500 (phase 2). Pattern match "((alter|create|drop)[[:space:]]+(column|database|procedure|table)|delete[[:space:]]+from|update.+set.+=)" at ARGS:body. [file "/usr/local/apache/conf/modsec2.user.conf"] [line "352"] [id "300015"] [rev "1"] [msg "Generic SQL injection protection"] [severity "CRITICAL"] [hostname "www.mysite.com"] [uri "/node/181/edit"] [unique_id "@TaVDEWnlusAABQv9@oAAAAD"] and here is /usr/local/apache/conf/modsec2.user.conf (line 352) #Generic SQL sigs SecRule ARGS "((alter|create|drop)[[:space:]]+(column|database|procedure|table)|delete[[:space:]]+from|update.+set.+=)" "id:1,rev:1,severity:2,msg:'Generic SQL injection protection'" The questions I have are: What should I do to "whitelist" or allow this rule to get through? What file do I create and where? How should I alter this rule? Can I set it to only be allowed for the one domain, since it is the only one having the issue on this dedicated server or is there a better way to exclude table tags perhaps? Thanks guys

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• Why can't I define a case-insensitve Dictionary in C#?

  - by Edward Tanguay

  This WPF code: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Windows; using System.Windows.Controls; using System.Windows.Data; using System.Windows.Documents; using System.Windows.Input; using System.Windows.Media; using System.Windows.Media.Imaging; using System.Windows.Navigation; using System.Windows.Shapes; namespace TestDict28342343 { public partial class Window1 : Window { public Window1() { InitializeComponent(); Dictionary<string, string> variableNamesAndValues = new Dictionary<string, string>(StringComparison.InvariantCultureIgnoreCase); } } } gives me the error: The best overloaded method match for 'System.Collections.Generic.Dictionary.Dictionary(System.Collections.Generic.IDictionary)' has some invalid arguments Yet I find this code example everywhere such as here and here. How can I define a Dictionary whose keys are case-insensitve?

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• what libraries or platforms should I use to build web apps that provide real-time, asynchronous data

  - by Daniel Sterling

  This is a less a question with a simple, practical answer and more a question to foster discussion on the real-time data exchange topic. I'll begin with an example: Google Wave is, at its core, a real-time asynchronous data synchronization engine. Wave supports (or plans to support) concurrent (real-time) document collaboration, disconnected (offline) document editing, conflict resolution, document history and playback with attribution, and server federation. A core part of Wave is the Operational Transformation engine: http://www.waveprotocol.org/whitepapers/operational-transform The OT engine manages document state. Changes between clients are merged and each client has a sane and consistent view of the document at all times; the final document is eventually consistent between all connected clients. My question is: is this system abstract or general enough to be used as a library or generic framework upon which to build web apps that synchronize real-time, asynchronous state in each client? Is the Wave protocol directly used by any current web applications (besides Google's client)? Would it make sense to directly use it for generic state synchronization in a web app? What other existing libraries or frameworks would you consider using when building such a web app? How much code in such an app might be domain-specific logic vs generic state synchronization logic? Or, put another way, how leaky might the state synchronization abstractions be? Comments and discussion welcomed!

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• object datasource problems in visual studio 2008,

  - by kamal

  After going to the process of adding the various attributes like insert,delete and update.But when i run it through the browser ,editing works but updating and deleting doesn't !(for the update and shows the same thing for delete,my friends think i need to use codes to repair the problems,can you help me please.it shows this: Server Error in '/WebSite3' Application. ObjectDataSource 'ObjectDataSource1' could not find a non-generic method 'Update' that has parameters: First_name, Surname, Original_author_id, First name, original_author id. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.InvalidOperationException: ObjectDataSource 'ObjectDataSource1' could not find a non-generic method 'Update' that has parameters: First_name, Surname, Original_author_id, First name, original_author id. Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Stack Trace: [InvalidOperationException: ObjectDataSource 'ObjectDataSource1' could not find a non-generic method 'Update' that has parameters: First_name, Surname, Original_author_id, First name, original_author id.] System.Web.UI.WebControls.ObjectDataSourceView.GetResolvedMethodData(Type type, String methodName, IDictionary allParameters, DataSourceOperation operation) +1119426 System.Web.UI.WebControls.ObjectDataSourceView.ExecuteUpdate(IDictionary keys, IDictionary values, IDictionary oldValues) +1008 System.Web.UI.DataSourceView.Update(IDictionary keys, IDictionary values, IDictionary oldValues, DataSourceViewOperationCallback callback) +92 System.Web.UI.WebControls.GridView.HandleUpdate(GridViewRow row, Int32 rowIndex, Boolean causesValidation) +907 System.Web.UI.WebControls.GridView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) +704 System.Web.UI.WebControls.GridView.OnBubbleEvent(Object source, EventArgs e) +95 System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +37 System.Web.UI.WebControls.GridViewRow.OnBubbleEvent(Object source, EventArgs e) +123 System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) +37 System.Web.UI.WebControls.LinkButton.OnCommand(CommandEventArgs e) +118

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• How to create a fully lazy singleton for generics

  - by Brendan Vogt

  I have the following code implementation of my generic singleton provider: public sealed class Singleton<T> where T : class, new() { Singleton() { } public static T Instance { get { return SingletonCreator.instance; } } class SingletonCreator { static SingletonCreator() { } internal static readonly T instance = new T(); } } This sample was taken from 2 articles and I merged the code to get me what I wanted: http://www.yoda.arachsys.com/csharp/singleton.html and http://www.codeproject.com/Articles/11111/Generic-Singleton-Provider. This is how I tried to use the code above: public class MyClass { public static IMyInterface Initialize() { if (Singleton<IMyInterface>.Instance == null // Error 1 { Singleton<IMyInterface>.Instance = CreateEngineInstance(); // Error 2 Singleton<IMyInterface>.Instance.Initialize(); } return Singleton<IMyInterface>.Instance; } } And the interface: public interface IMyInterface { } The error at Error 1 is: 'MyProject.IMyInterace' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method 'MyProject.Singleton<T>' The error at Error 2 is: Property or indexer 'MyProject.Singleton<MyProject.IMyInterface>.Instance' cannot be assigned to -- it is read only How can I fix this so that it is in line with the 2 articles mentioned above? Any other ideas or suggestions are appreciated.

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• Raw types and subtyping

  - by Dmitrii

  We have generic class SomeClass<T>{ } We can write the line: SomeClass s= new SomeClass<String>(); It's ok, because raw type is supertype for generic type. But SomeClass<String> s= new SomeClass(); is correct to. Why is it correct? I thought that type erasure was before type checking, but it's wrong. From Hacker's Guide to Javac When the Java compiler is invoked with default compile policy it performs the following passes: parse: Reads a set of *.java source files and maps the resulting token sequence into AST-Nodes. enter: Enters symbols for the definitions into the symbol table. process annotations: If Requested, processes annotations found in the specified compilation units. attribute: Attributes the Syntax trees. This step includes name resolution, type checking and constant folding. flow: Performs data ow analysis on the trees from the previous step. This includes checks for assignments and reachability. desugar: Rewrites the AST and translates away some syntactic sugar. generate: Generates Source Files or Class Files. Generic is syntax sugar, hence type erasure invoked at 6 pass, after type checking, which invoked at 4 pass. I'm confused.

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• Strange behavior with complex Q object filter queries in Django

  - by HWM-Rocker

  Hi I am trying to write a tagging system for Django, but today I encountered a strange behavior in filter or the Q object (django.db.models.Q). I wrote a function, that converts a search string into a Q object. The next step would be to filter the TaggedObject with these query. But unfortunately I get a strange behavior. when I search (id=20) = Q: (AND: ('tags__tag__id', 20)) and it returns 2 Taged Objects with the ID 1127 and 132 when I search (id=4) = Q: (AND: ('tags__tag__id', 4)) and it returns also 2 Objects, but this time 1180 and 1127 until here is everything fine, but when i make a little bit more complex query like (id=4) or (id=20) = Q: (OR: ('tags__tag__id', 4), ('tags__tag__id', 20)) then it returns 4(!) Objects 1180, 1127, 1127, 132 But the object with the ID 1127 is returned twice, but thats not the behaviour I want. Do I have to live with it, and uniqify that list or can I do something different. The representation of the Q object looks fine for me. But the worst is now, when I search for (id=20) and (id=4) = Q: (AND: ('tags__tag__id', 20), ('tags__tag__id', 4)) then it returns no object at all. But why? The representation should be ok and the object with the id 1127 is tagged by both. What am I missing? Here are also the relevant parts of the classes, that are involved: class TaggedObject(models.Model): """ class that represent a tagged object """ tags = generic.GenericRelation('ObjectTagBridge', blank=True, null=True) class ObjectTagBridge(models.Model): """ Help to connect a generic object to a Tag. """ # pylint: disable-msg=W0232,R0903 content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey('content_type', 'object_id') tag = models.ForeignKey('Tag') class Tag(models.Model): ... Thanks for your help

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• C# Fun with Generics - Mutual Dependencies

  - by Kenneth Cochran

  As an experiment I'm trying to write a generic MVP framework. I started with: public interface IPresenter<TView> where TView: IView<IPresenter<... { TView View { get; set;} } public interface IView<TPresenter> where TPresenter:IPresenter<IView<... { TPresenter Presenter { get; set; } } Obviously this can't work because the types of TView and TPresenter can't be resolved. You'd be writing Type<Type<... forever. So my next attempt looked like this: public interface IView<T> where T:IPresenter { ... } public interface IView:IView<IPresenter> { } public interface IPresenter<TView> where TView: IView { ... } public interface IPresenter: IPresenter<IView> { ... } This actually compiles and you can even inherit from these interfaces like so: public class MyView : IView, IView<MyPresenter> { ... } public class MyPresenter : IPresenter, IPresenter<MyView> { ... } The problem is in the class definition you have to define any members declared in the generic type twice. Not ideal but it still compiles. The problem's start creeping up when you actually try to access the members of a Presenter from a View or vice versa. You get an Ambiguous reference when you try to compile. Is there any way to avoid this double implementation of a member when you inherit from both interfaces? Is it even possible to resolve two mutually dependent generic types at compile time?

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• Best practice - logging events (general) and changes (database)

  - by b0x0rz

  need help with logging all activities on a site as well as database changes. requirements: * should be in database * should be easily searchable by initiator (user name / session id), event (activity type) and event parameters i can think of a database design but either it involves a lot of tables (one per event) so i can log each of the parameters of an event in a separate field OR it involves one table with generic fields (7 int numeric and 7 text types) and log everything in one table with event type field determining what parameter got written where (and hoping that i don't need more than 7 fields of a certain type, or 8 or 9 or whatever number i choose)... example of entries (the usual things): [username] login failed @datetime [username] login successful @datetime [username] changed password @datetime, estimated security of password [low/ok/high/perfect] @datetime [username] clicked result [result number] [result id] after searching for [search string] and got [number of results] @datetime [username] clicked result [result number] [result id] after searching for [search string] and got [number of results] @datetime [username] changed profile name from [old name] to [new name] @datetime [username] verified name with [credit card type] credit card @datetime datbase table [table name] purged of old entries @datetime via automated process etc... so anyone dealt with this before? any best practices / links you can share? i've seen it done with the generic solution mentioned above, but somehow that goes against what i learned from database design, but as you can see the sheer number of events that need to be trackable (each user will be able to see this info) is giving me headaches, BUT i do LOVE the one event per table solution more than the generic one. any thoughts? edit: also, is there maybe an authoritative list of such (likely) events somewhere? thnx stack overflow says: the question you're asking appears subjective and is likely to be closed. my answer: probably is subjective, but it is directly related to my issue i have with designing a database / writing my code, so i'd welcome any help. also i tried narrowing down the ideas to 2 so hopefully one of these will prevail, unless there already is an established solution for these kinds of things.

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• best practice - loging events (general) and changes (database)

  - by b0x0rz

  need help with logging all activities on a site as well as database changes. requirements: * should be in database * should be easily searchable by initiator (user name / session id), event (activity type) and event parameters i can think of a database design but either it involves a lot of tables (one per event) so i can log each of the parameters of an event in a separate field OR it involves one table with generic fields (7 int numeric and 7 text types) and log everything in one table with event type field determining what parameter got written where (and hoping that i don't need more than 7 fields of a certain type, or 8 or 9 or whatever number i choose)... example of entries (the usual things): [username] login failed @datetime [username] login successful @datetime [username] changed password @datetime, estimated security of password [low/ok/high/perfect] @datetime [username] clicked result [result number] [result id] after searching for [search string] and got [number of results] @datetime [username] clicked result [result number] [result id] after searching for [search string] and got [number of results] @datetime [username] changed profile name from [old name] to [new name] @datetime [username] verified name with [credit card type] credit card @datetime datbase table [table name] purged of old entries @datetime etc... so anyone dealt with this before? any best practices / links you can share? i've seen it done with the generic solution mentioned above, but somehow that goes against what i learned from database design, but as you can see the sheer number of events that need to be trackable (each user will be able to see this info) is giving me headaches, BUT i do LOVE the one event per table solution more than the generic one. any thoughts? edit: also, is there maybe an authoritative list of such (likely) events somewhere? thnx stack overflow says: the question you're asking appears subjective and is likely to be closed. my answer: probably is subjective, but it is directly related to my issue i have with designing a database / writing my code, so i'd welcome any help. also i tried narrowing down the ideas to 2 so hopefully one of these will prevail, unless there already is an established solution for these kinds of things.

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• Traversing through an arbitrary dictionary tree structure in C#

  - by Rudism

  I am trying to write a recursive C# function that will operate on generic dictionaries of the form IDictionary<string, T> where T is either another IDictionary<string, T> or a string. My first failed attempt looked something like this: public string HandleDict(IDictionary<string, string> dict){ // handle the leaf-node here } public string HandleDict<T>(IDictionary<string, IDictionary<string, T>> dict){ // loop through children foreach(string key in dict.Keys){ HandleDict(dict[key]); } } I also tried variants of HandleDict<T>(IDictionary<string, T>) where T : IDictionary<string, T> but that also doesn't quite work. I know that what I want to do could be achieved through a custom class as the parameter instead of dictionaries, and that my attempts are conceptually flawed (there's no end to the recursion in the generic function). I would still like to know if there is actually a way to do what I want here using just generic IDictionaries.

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