My.Application.DoEvents Method

Artykuł
11/16/2012

Processes all Windows messages currently in the message queue.

' Usage
My.Application.DoEvents()
' Declaration
Public Sub DoEvents()

Remarks

The My.Application.DoEvents method allows your application to handle other events that might be raised while you code runs. The My.Application.DoEvents method has the same behavior as the DoEvents method.

When you run a Windows Forms application, it creates a new form, which then waits for events to be handled. Each time the form handles an event, such as a button click, it processes all the code associated with that event. All other events wait in the queue. While your code handles the event, your application does not respond. For example, the window does not repaint if another window is dragged on top.

If you call My.Application.DoEvents in your code, your application can handle the other events. For example, if your code adds data to a ListBox in a loop, and after each step of the loop it calls My.Application.DoEvents, your form repaints when another window is dragged over it. If you remove My.Application.DoEvents from your code, your form will not repaint until the click event handler of the button is finished executing.

Typically, you use this method in a loop to process messages.

Note

The My.Application.DoEvents method does not process events in exactly the same way as the form does. Use multithreading to make the form directly handle the events. For more information, see Multithreading in Visual Basic.

Warning

If a method that handles a user interface (UI) event calls the My.Application.DoEvents method, the method might be re-entered before it finishes. This can happen because the My.Application.DoEvents method processes Windows messages, and Windows messages can raise events.

Tasks

The following table lists an example of a task involving the My.Application.DoEvents method.

To	See
Allow a form to respond to UI input while busy	Walkthrough: Handling Events

Example

This example uses the My.Application.DoEvents method to allow the UI for TextBox1 to update.

Private Sub TestDoEvents()
    For i As Integer = 0 To 10000
        TextBox1.Text = i.ToString
        My.Application.DoEvents()
    Next 
End Sub

This code should be in a form that has a TextBox1 component with a Text property.

Requirements

Namespace:Microsoft.VisualBasic.ApplicationServices

Class:WindowsFormsApplicationBase

Assembly: Visual Basic Runtime Library (in Microsoft.VisualBasic.dll)

Availability by Project Type

Project type	Available
Windows Application	Yes
Class Library	No
Console Application	No
Windows Control Library	No
Web Control Library	No
Windows Service	No
Web Site	No

Permissions

The following permissions may be necessary:

Permission	Description
FileIOPermission	Controls the ability to access files and folders. Associated enumeration: Unrestricted.
UIPermission	Controls the permissions related to user interfaces and the clipboard. Associated enumeration: AllWindows.

For more information, see Code Access Security and Requesting Permissions.

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