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  • Why not .NET-style delegates rather than closures in Java?

    - by h2g2java
    OK, this is going to be my beating a dying horse for the 3rd time. However, this question is different from my earlier two about closures/delegates, which asks about plans for delegates and what are the projected specs and implementation for closures. This question is about - why is the Java community struggling to define 3 different types of closures when we could simply steal the whole concept of delegates lock, stock and barrel from our beloved and friendly neighbour - Microsoft. There are two non-technical conclusions I would be very tempted to jump into: The Java community should hold up its pride, at the cost of needing to go thro convoluted efforts, by not succumbing to borrowing any Microsoft concepts or otherwise vindicate Microsoft's brilliance. Delegates is a Microsoft patented technology. Alright, besides the above two possibilities, Q1. Is there any weakness or inadequacy in msft-styled delegates that the three (or more) forms of closures would be addressing? Q2. I am asking this while shifting between java and c# and it intrigues me that c# delegates does exactly what I needed. Are there features that would be implemented in closures that are not currently available in C# delegates? If so what are they because I cannot see what I need more than what C# delegates has adequately provided me? Q3. I know that one of the concerns about implementing closures/delegates in java is the reduction of orthogonality of the language, where more than one way is exposed to perform a particular task. Is it worth the level convolution and time spent to avoid delegates just to ensure java retains its level of orthogonality? In SQL, we know that it is advisable to break orthogonality by frequently adequately satisfying only the 2nd normal form. Why can't java be subjected to reduction of orthogonality and OO-ness for the sake of simplicity? Q4. The architecture of JVM is technically constrained from implementing .NET-styled delegates. If this reason WERE (subjunctive to emphasize unlikelihood) true, then why can't the three closures proposals be hidden behind a simple delegate keyword or annotation: if we don't like to use @delegate, we could use @method. I cannot see how delegate statement format is more complex than the three closure proposals.

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  • Was delegates static by default?

    - by Sri Kumar
    Hello All, I was just trying to understand delegates using the following code. public class delegatesEx { public delegate int Mydelegate(int first, int second); public int add(int first, int second) { return first + second; } public int sub(int first, int second) { return first - second; } } Here is my main method Console.WriteLine("******** Delegates ************"); delegatesEx.Mydelegate myAddDelegates = new delegatesEx.Mydelegate(new delegatesEx().add); int addRes = myAddDelegates(3, 2); Console.WriteLine("Add :" + addRes); delegatesEx.Mydelegate mySubDelegates = new delegatesEx.Mydelegate(new delegatesEx().sub); int subRes = mySubDelegates(3, 2); Console.WriteLine("Sub :" + subRes); I didn't declare delegate to be static but i was able to access it using the Class name. How is it possible?

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  • Delegates doesnot work properly

    - by Warrior
    I am new to iphone development.I am covering the date to the desired format and set it to the delegates and get its value in the another view.The session restarts when i tried to get the value from delegates.If i set the original date and not the formatted date in the set delegate ,then i able to get the value in the another view.If i also give any static string value,then also i am able to the static string value back.Only the formatted date which is string is set then the session restarts.If i print and check the value of the formatted date it prints the correct formatted date only.Please help me out.Here is my code for date conversion NSString *dateval=[[stories objectAtIndex: storyIndex] objectForKey:@"date"]; NSDateFormatter *inputFormatter = [[NSDateFormatter alloc] init]; [inputFormatter setDateFormat:@"EEE, MMM dd, yyyy"]; NSDate *inputDate = [inputFormatter dateFromString:dateval]; NSDateFormatter *outputFormatter = [[NSDateFormatter alloc] init]; [outputFormatter setDateFormat:@"MMMM dd"]; NSString *outputDate = [outputFormatter stringFromDate:inputDate]; AppDelegate *delegate=(AppDelegate *)[[UIApplication sharedApplication]delegate]; [delegate setCurrentDates:outputDate]; Thanks.

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  • Implementation of delegates in C#

    - by Ram
    Hi, I am trying to learn on how to use delegates efficiently in C# and I was just wondering if anyone can guide me through... The following is a sample implementation using delegates... All I am doing is just passing a value through a delegate from one class to another... Please tell me if this is the right way to implement... And also your suggestions... Also, please note that I have de-registered the delegate in : void FrmSample_FormClosing(object sender, FormClosingEventArgs e) { sampleObj.AssignValue -= new Sample.AssignValueDelegate(AssignValue); } Is this de-registration necessary? The following is the code that I have written.. public partial class FrmSample : Form { Sample sampleObj; public FrmSample() { InitializeComponent(); this.Load += new EventHandler(FrmSample_Load); this.FormClosing += new FormClosingEventHandler(FrmSample_FormClosing); sampleObj = new Sample(); sampleObj.AssignValue = new Sample.AssignValueDelegate(AssignValue); } void FrmSample_FormClosing(object sender, FormClosingEventArgs e) { sampleObj.AssignValue -= new Sample.AssignValueDelegate(AssignValue); } void FrmSample_Load(object sender, EventArgs e) { sampleObj.LoadValue(); } void AssignValue(string value) { MessageBox.Show(value); } } class Sample { public delegate void AssignValueDelegate(string value); public AssignValueDelegate AssignValue; internal void LoadValue() { if (AssignValue != null) { AssignValue("This is a test message"); } } } Pls provide your feedback on whether this is right... Thanks, Ram

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  • Multithreaded Delegates/Events

    - by Matt
    I am trying to disable parts of the UI in a .NET app based on polling done on a background thread. The background thread checks to see if the global database connection the app uses is still open and operable. What I need to do, and would prefer to do it without polling on the UI thread, is to add an event handler that can be raised by the background thread if the connection status changes. That way, any form can have a handler that will disable those parts of the UI that require the connection to function. Attempting to use a straight event declaration in the class that holds the thread sub, and raising the event in the background thread causing cross-thread execution errors regarding accessing UI controls from other threads. Obviously, there is a correct way to do this, but we have limited experience with events (single threaded apps mainly), and almost none with delegates. I've read through documentation and examples for delegates, and it seems to be closer to what we need, but I'm not sure how to make it work in this instance. The app is written mainly in VB.NET, but an example or help in C# is fine too.

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  • What was your "aha moment" in understanding delegates?

    - by CM90
    Considering the use of delegates in C#, does anyone know if there is a performance advantage or if it is a convenience to the programmer? If we are creating an object that holds a method, it sounds as if that object would be a constant in memory to be called on, instead of loading the method every time it is called. For example, if we look at the following Unity3D-based code: public delegate H MixedTypeDelegate<G, H>(G g) public class MainParent : MonoBehaviour // Most Unity classes inherit from M.B. { public static Vector3 getPosition(GameObject g) { /* GameObject is a Unity class, and Vector3 is a struct from M.B. The "position" component of a GameObject is a Vector3. This method takes the GameObject I pass to it & returns its position. */ return g.transform.position; } public static MixedTypeDelegate<GameObject, Vector3> PositionOf; void Awake( ) // Awake is the first method called in Unity, always. { PositionOf = MixedTypeDelegate<GameObject, Vector3>(getPosition); } } public class GameScript : MainParent { GameObject g = new GameObject( ); Vector3 whereAmI; void Update( ) { // Now I can say: whereAmI = PositionOf(g); // Instead of: whereAmI = getPosition(g); } } . . . But that seems like an extra step - unless there's that extra little thing that it helps. I suppose the most succinct way to ask a second question would be to say: When you had your aha moment in understanding delegates, what was the context/scenario/source? Thank you!

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  • Delegates and ParamArray - Workaround Suggestions?

    - by M.A. Hanin
    Some predefined methods contain a ParamArray in their signature. Delegates, however, cannot contain a ParamArray in their signature. Main question: Assume you wish to create a delegation mechanism for a specific method which requires a ParamArray. How would you work around this constraint? "Bonus" question: Assume you wish to create a generalized delegation mechanism for all methods which require ParamArray, how would you do that?

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  • Please Explain .NET Delegates

    - by user275561
    So I read MSDN and Stack Overflow. I understand what the Action Delegate does in general but it is not clicking no matter how many examples I do. In general, the same goes for the idea of delegates. So here is my question. When you have a function like this: public GetCustomers(Action<IEnumerable<Customer>,Exception> callBack) { } What is this, and what should I pass to it?

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  • Using Delegates in C# (Part 1)

    - by rajbk
    This post provides a very basic introduction of delegates in C#. Part 2 of this post can be read here. A delegate is a class that is derived from System.Delegate.  It contains a list of one or more methods called an invocation list. When a delegate instance is “invoked” with the arguments as defined in the signature of the delegate, each of the methods in the invocation list gets invoked with the arguments. The code below shows example with static and instance methods respectively: Static Methods 1: using System; 2: using System.Linq; 3: using System.Collections.Generic; 4: 5: public delegate void SayName(string name); 6: 7: public class Program 8: { 9: [STAThread] 10: static void Main(string[] args) 11: { 12: SayName englishDelegate = new SayName(SayNameInEnglish); 13: SayName frenchDelegate = new SayName(SayNameInFrench); 14: SayName combinedDelegate =(SayName)Delegate.Combine(englishDelegate, frenchDelegate); 15: 16: combinedDelegate.Invoke("Tom"); 17: Console.ReadLine(); 18: } 19: 20: static void SayNameInFrench(string name) { 21: Console.WriteLine("J'ai m'appelle " + name); 22: } 23: 24: static void SayNameInEnglish(string name) { 25: Console.WriteLine("My name is " + name); 26: } 27: } We have declared a delegate of type SayName with return type of void and taking an input parameter of name of type string. On line 12, we create a new instance of this delegate which refers to a static method - SayNameInEnglish.  SayNameInEnglish has the same return type and parameter list as the delegate declaration.  Once a delegate is instantiated, the instance will always refer to the same target. Delegates are immutable. On line 13, we create a new instance of the delegate but point to a different static method. As you may recall, a delegate instance encapsulates an invocation list. You create an invocation list by combining delegates using the Delegate.Combine method (there is an easier syntax as you will see later). When two non null delegate instances are combined, their invocation lists get combined to form a new invocation list. This is done in line 14.  On line 16, we invoke the delegate with the Invoke method and pass in the required string parameter. Since the delegate has an invocation list with two entries, each of the method in the invocation list is invoked. If an unhandled exception occurs during the invocation of one of these methods, the exception gets bubbled up to the line where the invocation was made (line 16). If a delegate is null and you try to invoke it, you will get a System.NullReferenceException. We see the following output when the method is run: My name is TomJ'ai m'apelle Tom Instance Methods The code below outputs the same results as before. The only difference here is we are creating delegates that point to a target object (an instance of Translator) and instance methods which have the same signature as the delegate type. The target object can never be null. We also use the short cut syntax += to combine the delegates instead of Delegate.Combine. 1: public delegate void SayName(string name); 2: 3: public class Program 4: { 5: [STAThread] 6: static void Main(string[] args) 7: { 8: Translator translator = new Translator(); 9: SayName combinedDelegate = new SayName(translator.SayNameInEnglish); 10: combinedDelegate += new SayName(translator.SayNameInFrench); 11:  12: combinedDelegate.Invoke("Tom"); 13: Console.ReadLine(); 14: } 15: } 16: 17: public class Translator { 18: public void SayNameInFrench(string name) { 19: Console.WriteLine("J'ai m'appelle " + name); 20: } 21: 22: public void SayNameInEnglish(string name) { 23: Console.WriteLine("My name is " + name); 24: } 25: } A delegate can be removed from a combination of delegates by using the –= operator. Removing a delegate from an empty list or removing a delegate that does not exist in a non empty list will not result in an exception. Delegates are invoked synchronously using the Invoke method. We can also invoke them asynchronously using the BeginInvoke and EndInvoke methods which are compiler generated.

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  • Are delegates copied during assignment to an event?

    - by Sir Psycho
    Hi, The following code seems to execute the FileRetrieved event more than once. I thought delegates were a reference type. I was expecting this to execute once. I'm going to take a guess and say that the reference is being passed by value, therefore copied but I don't like guesswork :-) public delegate void DirListEvent<T>(T dirItem); void Main() { DirListEvent<string> printFilename = s => { Console.WriteLine (s); }; var obj = new DirectoryLister(); obj.FileRetrieved += printFilename; obj.FileRetrieved += printFilename; obj.GetDirListing(); } public class DirectoryLister { public event DirListEvent<string> FileRetrieved; public DirectoryLister() { FileRetrieved += delegate {}; } public void GetDirListing() { foreach (var file in Directory.GetFiles(@"C:\")) { FileRetrieved(file); } } }

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  • Are static delegates thread-safe?

    - by leypascua
    Consider this code snippet: public static class ApplicationContext { private static Func<TService> Uninitialized<TService>() { throw new InvalidOperationException(); } public static Func<IAuthenticationProvider> AuthenticationProvider = Uninitialized<IAuthenticationProvider>(); public static Func<IUnitOfWorkFactory> UnitOfWorkFactory = Uninitialized<IUnitOfWorkFactory>(); } //can also be in global.asax if used in a web app. public static void Main(string[] args) { ApplicationContext.AuthenticationProvider = () => new LdapAuthenticationProvider(); ApplicationContext.UnitOfWorkFactory = () => new EFUnitOfWorkFactory(); } //somewhere in the code.. say an ASP.NET MVC controller ApplicationContext.AuthenticationProvider().SignIn(username, true); Are delegates in the static class ApplicationContext thread-safe in the sense that multiple-threads can invoke them? What potential problems will I face if I pursue this approach?

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  • c# Delegates, Events and Lambda Expr for new students

    - by MarkP
    I've been asked by my pointy haired boss to educate our new co-ops (interns) in the ways of C#. I have roughly ~30mins to cover the topics of Delegates, Events and Lambda Expressions. The time restriction is rather tight and the topics are broad. Since I'm not a C# guru, I would like some hints and pointers. Since my time is short, what points should I cover with respect to the three topics listed above? What are some good Do's and Dont's when using those three things? I might have time for a short Lambda Expr demo. What is the most common use of LExpr (probably a Select().Where() statement on an enumerable??) that I could demo? Thanks. EDIT: The students have working knowledge of C++ and Java.

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  • Delegates in .NET: how are they constructed ?

    - by Saulius
    While inspecting delegates in C# and .NET in general, I noticed some interesting facts: Creating a delegate in C# creates a class derived from MulticastDelegate with a constructor: .method public hidebysig specialname rtspecialname instance void .ctor(object 'object', native int 'method') runtime managed { } Meaning that it expects the instance and a pointer to the method. Yet the syntax of constructing a delegate in C# suggests that it has a constructor new MyDelegate(int () target) where I can recognise int () as a function instance (int *target() would be a function pointer in C++). So obviously the C# compiler picks out the correct method from the method group defined by the function name and constructs the delegate. So the first question would be, where does the C# compiler (or Visual Studio, to be precise) pick this constructor signature from ? I did not notice any special attributes or something that would make a distinction. Is this some sort of compiler/visualstudio magic ? If not, is the T (args) target construction valid in C# ? I did not manage to get anything with it to compile, e.g.: int () target = MyMethod; is invalid, so is doing anything with MyMetod, e.g. calling .ToString() on it (well this does make some sense, since that is technically a method group, but I imagine it should be possible to explicitly pick out a method by casting, e.g. (int())MyFunction. So is all of this purely compiler magic ? Looking at the construction through reflector reveals yet another syntax: Func CS$1$0000 = new Func(null, (IntPtr) Foo); This is consistent with the disassembled constructor signature, yet this does not compile! One final interesting note is that the classes Delegate and MulticastDelegate have yet another sets of constructors: .method family hidebysig specialname rtspecialname instance void .ctor(class System.Type target, string 'method') cil managed Where does the transition from an instance and method pointer to a type and a string method name occur ? Can this be explained by the runtime managed keywords in the custom delegate constructor signature, i.e. does the runtime do it's job here ?

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  • Different behavior of reflected generic delegates with and without debugger

    - by Andrew_B
    Hello. We have encountered some strange things while calling reflected generic delegates. In some cases with attatched debuger we can make impossible call, while without debugger we cannot catch any exception and application fastfails. Here is the code: using System; using System.Windows.Forms; using System.Reflection; namespace GenericDelegate { public partial class Form1 : Form { public Form1() { InitializeComponent(); } private delegate Class2 Delegate1(); private void button1_Click(object sender, EventArgs e) { MethodInfo mi = typeof (Class1<>).GetMethod("GetClass", BindingFlags.NonPublic | BindingFlags.Static); if (mi != null) { Delegate1 del = (Delegate1) Delegate.CreateDelegate(typeof (Delegate1), mi); MessageBox.Show("1"); try { del(); } catch (Exception) { MessageBox.Show("No, I can`t catch it"); } MessageBox.Show("2"); mi.Invoke(null, new object[] {});//It's Ok, we'll get exception here MessageBox.Show("3"); } } class Class2 { } class Class1<T> : Class2 { internal static Class2 GetClass() { Type type = typeof(T); MessageBox.Show("Type name " + type.FullName +" Type: " + type + " Assembly " + type.Assembly); return new Class1<T>(); } } } } There are two problems: Behavior differs with debugger and without You cannot catch this error without debugger by clr tricks. It's just not the clr exception. There are memory acces vialation, reading zero pointer inside of internal code. Use case: You develop something like plugins system for your app. You read external assembly, find suitable method in some type, and execute it. And we just forgot about that we need to check up is the type generic or not. Under VS (and .net from 2.0 to 4.0) everything works fine. Called function does not uses static context of generic type and type parameters. But without VS application fails with no sound. We even cannot identify call stack attaching debuger. Tested with .net 4.0 The question is why VS catches but runtime do not?

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  • iperf max udp multicast performance peaking at 10Mbit/s?

    - by Tom Frey
    I'm trying to test UDP multicast throughput via iperf but it seems like it's not sending more than 10Mbit/s from my dev machine: C:\> iperf -c 224.0.166.111 -u -T 1 -t 100 -i 1 -b 1000000000 ------------------------------------------------------------ Client connecting to 224.0.166.111, UDP port 5001 Sending 1470 byte datagrams Setting multicast TTL to 1 UDP buffer size: 8.00 KByte (default) ------------------------------------------------------------ [156] local 192.168.1.99 port 49693 connected with 224.0.166.111 port 5001 [ ID] Interval Transfer Bandwidth [156] 0.0- 1.0 sec 1.22 MBytes 10.2 Mbits/sec [156] 1.0- 2.0 sec 1.14 MBytes 9.57 Mbits/sec [156] 2.0- 3.0 sec 1.14 MBytes 9.55 Mbits/sec [156] 3.0- 4.0 sec 1.14 MBytes 9.56 Mbits/sec [156] 4.0- 5.0 sec 1.14 MBytes 9.56 Mbits/sec [156] 5.0- 6.0 sec 1.15 MBytes 9.62 Mbits/sec [156] 6.0- 7.0 sec 1.14 MBytes 9.53 Mbits/sec When I run it on another server, I'm getting ~80Mbit/s which is quite a bit better but still not anywhere near the 1Gbps limits that I should be getting? C:\> iperf -c 224.0.166.111 -u -T 1 -t 100 -i 1 -b 1000000000 ------------------------------------------------------------ Client connecting to 224.0.166.111, UDP port 5001 Sending 1470 byte datagrams Setting multicast TTL to 1 UDP buffer size: 8.00 KByte (default) ------------------------------------------------------------ [180] local 10.0.101.102 port 51559 connected with 224.0.166.111 port 5001 [ ID] Interval Transfer Bandwidth [180] 0.0- 1.0 sec 8.60 MBytes 72.1 Mbits/sec [180] 1.0- 2.0 sec 8.73 MBytes 73.2 Mbits/sec [180] 2.0- 3.0 sec 8.76 MBytes 73.5 Mbits/sec [180] 3.0- 4.0 sec 9.58 MBytes 80.3 Mbits/sec [180] 4.0- 5.0 sec 9.95 MBytes 83.4 Mbits/sec [180] 5.0- 6.0 sec 10.5 MBytes 87.9 Mbits/sec [180] 6.0- 7.0 sec 10.9 MBytes 91.1 Mbits/sec [180] 7.0- 8.0 sec 11.2 MBytes 94.0 Mbits/sec Anybody has any idea why this is not achieving close to link limits (1Gbps)? Thanks, Tom

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  • Lambda expressions as CLR (.NET) delegates / event handlers in Visual C++ 2010

    - by absence
    Is it possible to use the new lambda expressions in Visual C++ 2010 as CLR event handlers? I've tried the following code: SomeEvent += gcnew EventHandler( [] (Object^ sender, EventArgs^ e) { // code here } ); It results in the following error message: error C3364: 'System::EventHandler' : invalid argument for delegate constructor; delegate target needs to be a pointer to a member function Am I attempting the impossible, or is simply my syntax wrong?

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  • Problem using delegates, static, and dependencyproperties

    - by red-X
    I'm trying to animate a private variable named radius, which works. However while its changing I'm trying to execute a function which is getting to be quite of a problem. the code i have is below, it wont run because it has the following error An object reference is required for the non-static field, method, or property 'AppPart.SetChildrenPosition()' specifically new SetChildrenPositionDelegate(SetChildrenPosition) this part in this sentance part.Dispatcher.BeginInvoke(new SetChildrenPositionDelegate(SetChildrenPosition), new Object()); thnx to anyone able to help me. class AppPart : Shape { public string name { get; set; } public List<AppPart> parts { get; set; } private double radius { get { return (double)GetValue(radiusProperty); } set { SetValue(radiusProperty, value); } } public static readonly DependencyProperty radiusProperty = DependencyProperty.Register( "radius", typeof(double), typeof(AppPart), new PropertyMetadata( new PropertyChangedCallback(radiusChangedCallback))); private delegate void SetChildrenPositionDelegate(); private void SetChildrenPosition() { //do something with radius } private static void radiusChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e) { AppPart part = d as AppPart; part.Dispatcher.BeginInvoke(new SetChildrenPositionDelegate(SetChildrenPosition), new Object()); } private void AnimateRadius(double start, double end) { DoubleAnimation ani = new DoubleAnimation(); ani.From = start; ani.To = end; ani.FillBehavior = FillBehavior.HoldEnd; ani.Duration = new Duration(new TimeSpan(0, 0, 0, 3, 0)); ani.Completed += delegate { Console.WriteLine("ani ended"); }; this.BeginAnimation(AppPart.radiusProperty, ani); } }

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  • Understanding AddHandler and pass delegates and events.

    - by Achilles
    I am using AddHandler to wire a function to a control's event that I dynamically create: Public Sub BuildControl(EventHandler as System.Delegate) dim objMyButton as new button AddHandler objMyButton.Click, EventHandler end Sub This code is generating a run-time exception stating: Unable to cast object of type 'MyEventHandlerDelegate' to type 'System.EventHandler' What am I not understanding about System.Delegate even though AddHandler takes as an argument of type "System.Delegate"? What Type does "EventHandler need to be to cast to a type that AddHandler can accept? Thanks for your help!

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  • A question on delegates and method parameters

    - by Srinivas Reddy Thatiparthy
    public class Program { delegate void Srini(string param); static void Main(string[] args) { Srini sr = new Srini(PrintHello1); sr += new Srini(PrintHello2); //case 2: sr += new Srini(delegate(string o) { Console.WriteLine(o); }); sr += new Srini(delegate(object o) { Console.WriteLine(o.ToString()); }); //case 4: sr += new Srini(delegate { Console.WriteLine(“This line is accepted,though the method signature is not Comp”); });//case 5 sr("Hello World"); Console.Read(); } static void PrintHello1(string param) { Console.WriteLine(param); } static void PrintHello2(object param) { Console.WriteLine(param); } } Compiler doesn't complain about the case 2(see the comment),well,the reason is straight forward since string inherits from object. ,along the same lines ,Why is it complaining for anonymous method types(see the comment //case 4:) that “Cannot convert anonymous method to delegate type 'DelegateTest.Program.Srini' because the parameter types do not match the delegate parameter types” where as in case of normal method it doesn't ?or am i comparing apples with oranges? Another case is why is it accepting anonymous method without parameters?

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  • Logging class using delegates (NullReferenceException)

    - by Leroy Jenkins
    I have created a small application but I would now like to incorporate some type of logging that can be viewed via listbox. The source of the data can be sent from any number of places. I have created a new logging class that will pass in a delegate. I think Im close to a solution but Im receiving a NullReferenceException and I don’t know the proper solution. Here is an example of what Im trying to do: Class1 where the inbound streaming data is received. class myClass { OtherClass otherClass = new OtherClass(); otherClass.SendSomeText(myString); } Logging Class class OtherClass { public delegate void TextToBox(string s); TextToBox textToBox; Public OtherClass() { } public OtherClass(TextToBox ttb) { textToBox = ttb; } public void SendSomeText(string foo) { textToBox(foo); } } The Form public partial class MainForm : Form { OtherClass otherClass; public MainForm() { InitializeComponent(); otherClass = new OtherClass(this.TextToBox); } public void TextToBox(string pString) { listBox1.Items.Add(pString); } } Whenever I receive data in myClass, its throwing an error. Any help you could give would be appreciated.

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  • When using delegates, need better way to do sequential processing

    - by Padawan
    I have a class WebServiceCaller that uses NSURLConnection to make asynchronous calls to a web service. The class provides a delegate property and when the web service call is done, it calls a method webServiceDoneWithXXX on the delegate. There are several web service methods that can be called, two of which are say GetSummary and GetList. The classes that use WebServiceCaller initially need both the summary and list so they are written like this: -(void)getAllData { [webServiceCaller getSummary]; } -(void)webServiceDoneWithGetSummary { [webServiceCaller getList]; } -(void)webServiceDoneWithGetList { ... } This works but there are at least two problems: The calls are split across delegate methods so it's hard to see the sequence at a glance but more important it's hard to control or modify the sequence. Sometimes I want to call just GetSummary and not also GetList so I would then have to use an ugly class-level state variable that tells webServiceDoneWithGetSummary whether to call GetList or not. Assume that GetList cannot be done until GetSummary completes and returns some data which is used as input to GetList. Is there a better way to handle this and still get asynchronous calls? Update based on Matt Long's answer: Using notifications instead of a delegate, it looks like I can solve problem #2 by setting a different selector depending on whether I want the full sequence (GetSummary+GetList) or just GetSummary. Both observers would still use the same notification name when calling GetSummary. I would have to write two separate methods to handle GetSummaryDone instead of using a single delegate method (where I would have needed some class-level variable to tell whether to then call GetList). -(void)getAllData { [[NSNotificationCenter defaultCenter] addObserver:self              selector:@selector(getSummaryDoneAndCallGetList:)                  name:kGetSummaryDidFinish object:nil];     [webServiceCaller getSummary]; } -(void)getSummaryDoneAndCallGetList { [NSNotificationCenter removeObserver] //process summary data [[NSNotificationCenter defaultCenter] addObserver:self              selector:@selector(getListDone:)                  name:kGetListDidFinish object:nil];     [webServiceCaller getList]; } -(void)getListDone { [NSNotificationCenter removeObserver] //process list data } -(void)getJustSummaryData { [[NSNotificationCenter defaultCenter] addObserver:self              selector:@selector(getJustSummaryDone:) //different selector but                  name:kGetSummaryDidFinish object:nil]; //same notification name     [webServiceCaller getSummary]; } -(void)getJustSummaryDone { [NSNotificationCenter removeObserver] //process summary data } I haven't actually tried this yet. It seems better than having state variables and if-then statements but you have to write more methods. I still don't see a solution for problem 1.

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