Avoiding InvokeRequired

Igor Pashchuk, MBA

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27 Apr 2012CPOL

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Introduction

This minor article is an enhancement to the excellent piece of work by Pablo Grisafi. The goal is to enhance Pablo's code to work in cases where controls are not all created on the same (usually "UI") thread.

Using the code

The enhancement is relatively minor and virtually everyone with enough understanding of delegates and generics could easily enhance Pablo's version as I did below. While Pablo's version works for 95+% cases, in very special circumstances, a control might need to be created on another thread, thus requiring InvokeRequired check on that control's property -- not on the form's. The idea behind these enhancements is to allow the extension method to handle this type of scenario.

The code below helps ensure that all controls are updated on the thread on which they were created even when they were created on different threads.

static class ControlExtensions
{
  public static void InvokeOnOwnerThread<T>(this T control, Action<T> invoker) where T : Control
  {
    if (control.InvokeRequired)
      control.Invoke(invoker, control);
    else
      invoker(control);
  }
}

The code that uses this extension method would look like this:

private void UpdateFormTextFromSomeThread(string message)
{
  this.InvokeOnOwnerThread((form) => form.Text = message);  
}

History

No changes.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By

Igor Pashchuk, MBA

Software Developer (Senior) Credit Suisse

United States

I was introduced to computer programming at the age of 12 although I did not become particularly interested in software development until I turned 19 when I used one of my electives to take a computer science class. Since then, I never stopped writing software. My current interests are .NET, patterns and practices, and agile development (TDD and BDD).

Module InvokeRequiredHandler ''' <summary> ''' Provides a thread-safe call to form elements/controls. [Templated Method] ''' </summary> ''' <param name="controlToInvoke">(As T) Name of the form element/control to invoke.</param> ''' <param name="actionToPerform">(As Action(Of T)) Action to perform on the form element.</param> ''' <remarks>Example Usage: ''' <c>Public SomeElement As SomeControl</c> ''' <c>Private SomeElement2 As SomeControl</c> ''' <c>SomeElement.HandleInvokeRequired(Sub(SomeElement As SomeControl) SomeElement.Text = "Text Here")</c> ''' <c>SomeElement2.HandleInvokeRequired(Sub(SomeElement2 As SomeControl) SomeElement2.Enabled = False)</c> ''' </remarks> <System.Runtime.CompilerServices.Extension()> _ Public Sub HandleInvokeRequired(Of T As {Control, ISynchronizeInvoke}) _ (ByVal controlToInvoke As T, ByVal actionToPerform As Action(Of T)) 'Check to see if the control's InvokeRequired property is true If controlToInvoke.InvokeRequired Then 'Use Invoke() to invoke your action controlToInvoke.Invoke(actionToPerform, New Object() {controlToInvoke}) Else 'Check to ensure the control's handle is created If Not controlToInvoke.IsHandleCreated Then Return End If 'Check to ensure the control has not been disposed If controlToInvoke.IsDisposed Then Throw New ObjectDisposedException(String.Format("{0} is disposed.", controlToInvoke)) End If 'Perform the action actionToPerform(controlToInvoke) End If End Sub End Module

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Avoiding InvokeRequired

Introduction

Using the code

History

License

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