Automating the InvokeRequired code pattern

Question

I have become painfully aware of just how often one needs to write the following code pattern in event-driven GUI code  where  private void DoGUISwitch            cruisin for a bruisin  through exception city     object1 Visible   true      object2 Visible   false      becomes   private void DoGUISwitch         if  object1 InvokeRequired            object1 Invoke new MethodInvoker      gt    DoGUISwitch               else           object1 Visible   true          object2 Visible   false            This is an awkward pattern in C   both to remember  and to type  Has anyone come up with some sort of shortcut or construct that automates this to a degree  It d be cool if there was a way to attach a function to objects that does this check without having to go through all this extra work  like a object1 InvokeIfNecessary visible   true type shortcut   Previous answers have discussed the impracticality of just calling Invoke   every time  and even then the Invoke   syntax is both inefficient and still awkward to deal with   So  has anyone figured out any shortcuts

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You could write an extension method   public static void InvokeIfRequired this Control c  Action lt Control gt  action        if c InvokeRequired                c Invoke new Action      gt  action c               else               action c             And use it like this   object1 InvokeIfRequired c   gt    c Visible   true        EDIT  As Simpzon points out in the comments you could also change the signature to   public static void InvokeIfRequired lt T gt  this T c  Action lt T gt  action       where T   Control

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I d rather use a single instance of a method Delegate instead of creating a new instance every time  In my case i used to show progress and  info error  messages from a Backroundworker copying and casting large data from a sql instance  Everywhile after about 70000 progress and message calls my form stopped working and showing new messages  This didn t occure when i started using a single global instance delegate   delegate void ShowMessageCallback string message    private void Form1 Load object sender  EventArgs e        ShowMessageCallback showMessageDelegate   new ShowMessageCallback ShowMessage      private void ShowMessage string message        if  this InvokeRequired          this Invoke showMessageDelegate  message       else         labelMessage Text   message                void Message OnMessage object sender  Utilities Message MessageEventArgs e        ShowMessage e Message

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You should never be writing code that looks like this   private void DoGUISwitch         if  object1 InvokeRequired            object1 Invoke new MethodInvoker      gt    DoGUISwitch               else           object1 Visible   true          object2 Visible   false            If you do have code that looks like this then your application is not thread-safe   It means that you have code which is already calling DoGUISwitch   from a different thread   It s too late to be checking to see if it s in a different thread   InvokeRequire must be called BEFORE you make a call to DoGUISwitch   You should not access any method or property from a different thread   Reference  Control InvokeRequired Property where you can read the following      In addition to the InvokeRequired property  there are four methods on   a control that are thread safe to call  Invoke  BeginInvoke  EndInvoke   and CreateGraphics if the handle for the control has already been   created    In a single CPU architecture there s no problem  but in a multi-CPU architecture you can cause part of the UI thread to be assigned to the processor where the calling code was running   and if that processor is different from where the UI thread was running then when the calling thread ends Windows will think that the UI thread has ended and will kill the application process i e  your application will exit without error

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Here s the form I ve been using in all my code   private void DoGUISwitch          Invoke    MethodInvoker   delegate           object1 Visible   true          object2 Visible   false               I ve based this on the blog entry here   I have not had this approach fail me  so I see no reason to complicate my code with a check of the InvokeRequired property   Hope this helps

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Lee s approach can be simplified further  public static void InvokeIfRequired this Control control  MethodInvoker action           See Update 2 for edits Mike de Klerk suggests to insert here       if  control InvokeRequired            control Invoke action         else           action              And can be called like this  richEditControl1 InvokeIfRequired      gt           Do anything you want with the control here     richEditControl1 RtfText   value      RtfHelpers AddMissingStyles richEditControl1         There is no need to pass the control as parameter to the delegate  C  automatically creates a closure     UPDATE   According to several other posters Control can be generalized as ISynchronizeInvoke   public static void InvokeIfRequired this ISynchronizeInvoke obj                                           MethodInvoker action        if  obj InvokeRequired            var args   new object 0           obj Invoke action  args         else           action              DonBoitnott pointed out that unlike Control the ISynchronizeInvoke interface requires an object array for the Invoke method as parameter list for the action     UPDATE 2  Edits suggested by Mike de Klerk  see comment in 1st code snippet for insert point       When the form  thus the control  isn t visible yet  InvokeRequired  returns false     resulting still in a cross-thread exception  while   control Visible        System Threading Thread Sleep 50       See ToolmakerSteve s comment below for concerns about this suggestion

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Usage   control InvokeIfRequired c   gt  c Visible   false    return control InvokeIfRequired c   gt        c Visible   value      return c Visible        Code   using System  using System ComponentModel   namespace Extensions       public static class SynchronizeInvokeExtensions               public static void InvokeIfRequired lt T gt  this T obj  Action lt T gt  action              where T   ISynchronizeInvoke                       if  obj InvokeRequired                                obj Invoke action  new object     obj                               else                               action obj                                    public static TOut InvokeIfRequired lt TIn  TOut gt  this TIn obj  Func lt TIn  TOut gt  func               where TIn   ISynchronizeInvoke                       return obj InvokeRequired                    TOut obj Invoke func  new object     obj                      func obj

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I Kind of like to do it a bit different  i like to call  myself  if needed with an Action        private void AddRowToListView ScannerRow row  bool suspend                if  IsFormClosing              return           if  this InvokeRequired                        var A   new Action      gt  AddRowToListView row  suspend                this Invoke A               return                       as of here the Code is thread-safe   this is a handy pattern  the IsFormClosing is a field that i set to True when I am closing my form as there might be some background threads that are still running

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Here s an improved combined version of Lee s  Oliver s and Stephan s answers   public delegate void InvokeIfRequiredDelegate lt T gt  T obj      where T   ISynchronizeInvoke   public static void InvokeIfRequired lt T gt  this T obj  InvokeIfRequiredDelegate lt T gt  action      where T   ISynchronizeInvoke       if  obj InvokeRequired                obj Invoke action  new object     obj               else               action obj              The template allows for flexible and cast-less code which is much more readable while the dedicated delegate provides efficiency   progressBar1 InvokeIfRequired o   gt         o Style   ProgressBarStyle Marquee      o MarqueeAnimationSpeed   40

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Create a ThreadSafeInvoke snippet file  and then you can just select the update statements  right click and select  Surround With     or Ctrl-K S    lt  xml version  1 0  encoding  utf-8    gt   lt CodeSnippet Format  1 0 0  xmlns  http   schemas microsoft com VisualStudio 2005 CodeSnippet  gt     lt Header gt       lt Title gt ThreadsafeInvoke lt  Title gt       lt Shortcut gt  lt  Shortcut gt       lt Description gt Wraps code in an anonymous method passed to Invoke for Thread safety  lt  Description gt       lt SnippetTypes gt         lt SnippetType gt SurroundsWith lt  SnippetType gt       lt  SnippetTypes gt     lt  Header gt     lt Snippet gt       lt Code Language  CSharp  gt         lt   CDATA        Invoke   MethodInvoker  delegate                    selected                           gt       lt  Code gt     lt  Snippet gt   lt  CodeSnippet gt

[c#] Automating the InvokeRequired code pattern

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