WindowsApi:PeekMessage

lastmod 2016-04-13created 2016-04-132 edits

Clear message queue

Removing all Windows Messages from the Message Queue

While developing a Mobile Application, I had a case where a certain event took about 3 seconds from when it fired until it finished, and I needed to prevent other events from firing during that time. The first thing I tried was setting Form.Enable = false and setting it back to true after 3 seconds. In this case, the events fired after the 3 seconds passed. So I looked for a way to remove all Messages from the Message Queue.

The first thing that came to mind was IMessageFilter, the message-related interface, but this interface is not provided in the Compact Framework. I found code that implements IMessageFilter directly to receive Messages, but that code required passing a Control as a parameter. Unfortunately (?), this code (which takes a Control as a parameter) could not be used in the Application I was developing. So I searched again and found the method below.

struct MSG
{
    IntPtr hwnd;
    uint message;
    IntPtr wParam;
    IntPtr lParam;
    int time;
    int ptX;
    int ptY;
}

[DllImport("coredll")]
extern static bool PeekMessage(out MSG Msg, uint hWnd, uint
wMsgFilterMin, uint wMsgFilterMax, uint wRemoveMsg);

const uint PM_REMOVE = 1;

public static void ClearMessages()
{
    MSG msg;
    while (PeekMessage(out msg, 0, 0, 0, PM_REMOVE)) ;
}

Here you can see that because the Message structure is not defined in the Compact Framework, a struct called MSG was created manually, and that PM_REMOVE(1) is a parameter that removes ~~all messages~~ one message from the Message Queue.

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