Visual Basic .NET Language Threading Performing thread-safe calls using Control.Invoke()
Example
Using the Control.Invoke() method you may move the execution of a method or function from a background thread to the thread that the control was created on, which is usually the UI (User Interface) thread. By doing so your code will be queued to run on the control's thread instead, which removes the possibility of concurrency.
The Control.InvokeRequired property should also be checked in order to determine whether you need to invoke, or if the code is already running on the same thread as the control.
The Invoke() method takes a delegate as its first parameter. A delegate holds the reference, parameter list and return type to another method.
In Visual Basic 2010 (10.0) or higher, lambda expressions can be used to create a delegate method on the fly:
If LogTextBox.InvokeRequired = True Then
LogTextBox.Invoke(Sub() LogTextBox.AppendText("Check passed"))
Else
LogTextBox.AppendText("Check passed")
End If
Whereas in Visual Basic 2008 (9.0) or lower, you have to declare the delegate on your own:
Delegate Sub AddLogText(ByVal Text As String)
If LogTextBox.InvokeRequired = True Then
LogTextBox.Invoke(New AddLogText(AddressOf UpdateLog), "Check passed")
Else
UpdateLog("Check passed")
End If
Sub UpdateLog(ByVal Text As String)
LogTextBox.AppendText(Text)
End Sub
