Control.BeginInvoke Method (Delegate) (System.Windows.Forms)

BeginInvoke Method (Delegate)

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Microsoft Visual Studio 2008/.NET Framework 3.5

Other versions are also available for the following:

.NET Framework Class Library

Control..::.BeginInvoke Method (Delegate)

Updated: November 2007

Executes the specified delegate asynchronously on the thread that the control's underlying handle was created on.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)

Syntax

Visual Basic (Declaration)

Public Function BeginInvoke ( _
    method As Delegate _
) As IAsyncResult

Visual Basic (Usage)

Dim instance As Control
Dim method As [Delegate]
Dim returnValue As IAsyncResult

returnValue = instance.BeginInvoke(method)

public IAsyncResult BeginInvoke(
    Delegate method
)

Visual C++

public:
IAsyncResult^ BeginInvoke(
    Delegate^ method
)

public IAsyncResult BeginInvoke(
    Delegate method
)

JScript

public function BeginInvoke(
    method : Delegate
) : IAsyncResult

Parameters

method: Type: System..::.Delegate
A delegate to a method that takes no parameters.

Return Value

Type: System..::.IAsyncResult

An IAsyncResult that represents the result of the BeginInvoke operation.

Remarks

The delegate is called asynchronously, and this method returns immediately. You can call this method from any thread, even the thread that owns the control's handle. If the control's handle does not exist yet, this method searches up the control's parent chain until it finds a control or form that does have a window handle. If no appropriate handle can be found, BeginInvoke will throw an exception. Exceptions within the delegate method are considered untrapped and will be sent to the application's untrapped exception handler.

Note:
Most methods on a control can only be called from the thread where the control was created. In addition to the InvokeRequired property, there are four methods on a control that are thread safe: Invoke, BeginInvoke, EndInvoke, and CreateGraphics if the handle for the control has already been created. Calling CreateGraphics before the control's handle has been created on a background thread can cause illegal cross thread calls. For all other method calls, you should use one of the invoke methods to marshal the call to the control's thread. The invoke methods always invoke their callbacks on the control's thread.

Note:

Most methods on a control can only be called from the thread where the control was created. In addition to the InvokeRequired property, there are four methods on a control that are thread safe: Invoke, BeginInvoke, EndInvoke, and CreateGraphics if the handle for the control has already been created. Calling CreateGraphics before the control's handle has been created on a background thread can cause illegal cross thread calls. For all other method calls, you should use one of the invoke methods to marshal the call to the control's thread. The invoke methods always invoke their callbacks on the control's thread.

Note:
An exception might be thrown if the thread that should process the message is no longer active.

Examples

The following code example demonstrates a use of the BeginInvoke method.

Visual Basic

Delegate Sub InvokeDelegate()

Private Sub Invoke_Click(sender As Object, e As EventArgs)
   myTextBox.BeginInvoke(New InvokeDelegate(AddressOf InvokeMethod))
End Sub 'Invoke_Click

Public Sub InvokeMethod()
   myTextBox.Text = "Executed the given delegate"
End Sub 'InvokeMethod

public delegate void InvokeDelegate();

private void Invoke_Click(object sender, EventArgs e)
{
   myTextBox.BeginInvoke(new InvokeDelegate(InvokeMethod));
}
public void InvokeMethod()
{
   myTextBox.Text = "Executed the given delegate";
}

Visual C++

private:
   void Invoke_Click( Object^ /*sender*/, EventArgs^ /*e*/ )
   {
      myTextBox->BeginInvoke( gcnew InvokeDelegate( this, &MyForm::InvokeMethod ) );
   }

   void InvokeMethod()
   {
      myTextBox->Text = "Executed the given delegate";
   }

Permissions

SecurityPermission
for the immediate caller to call unmanaged code. Associated enumeration: SecurityPermissionFlag..::.UnmanagedCode

Platforms

Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information