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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)

public static void AddMessageFilter(
	IMessageFilter value
)

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 : IMessageFilter
{
    public bool PreFilterMessage(ref Message m)
    {
        // Blocks all the messages relating to the left mouse button. 
        if (m.Msg >= 513 && m.Msg <= 515)
        {
            Console.WriteLine("Processing the messages : " + m.Msg);
            return true;
        }
        return false;
    }
}

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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