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AddMessageFilter Method

Application.AddMessageFilter Method

Adds a message filter to monitor Windows messages as they are routed to their destinations.

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

'Declaration
Public Shared Sub AddMessageFilter ( _
	value As IMessageFilter _
)

Parameters

value
Type: System.Windows.Forms.IMessageFilter

The implementation of the IMessageFilter interface you want to install.

Use a message filter to prevent specific events from being raised or to perform special operations for an event before it is passed to an event handler. Message filters are unique to a specific thread.

To prevent a message from being dispatched, the value parameter instance that you pass to this method must override the PreFilterMessage method with the code to handle the message. The method must return false.

Caution noteCaution

Adding message filters to the message pump for an application can degrade performance.

The following code example creates a message filter called TestMessageFilter. This filter blocks all messages relating to the left mouse button. Before you can use a message filter, you must provide an implementation for the IMessageFilter interface.

' Creates a message filter.
<SecurityPermission(SecurityAction.LinkDemand, Flags := SecurityPermissionFlag.UnmanagedCode)> _
Public Class TestMessageFilter
    Implements IMessageFilter

    <SecurityPermission(SecurityAction.Demand)> _
    Public Function PreFilterMessage(ByRef m As System.Windows.Forms.Message) _
    As Boolean Implements IMessageFilter.PreFilterMessage
        ' Blocks all the messages relating to the left mouse button. 
        If ((m.Msg >= 513) And (m.Msg <= 515)) Then
            Console.WriteLine("Processing the messages : " & m.Msg)
            Return True 
        End If 
        Return False 
    End Function 
End Class

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

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