Do you use WM_NULL?
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  1. #1
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    Talking Do you use WM_NULL?

    I have found funny windows message.
    It is described in MSDN so:

    WM_NULL
    The WM_NULL message performs no operation. An application sends the WM_NULL message if it wants to post a message that the recipient window will ignore.

    I propose competition on the best idea how to use it

  2. #2
    ovidiucucu's Avatar
    ovidiucucu is offline Moderator/Reviewer Power Poster
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    Better, read all the documentation before -ing and say "funny".
    From MSDN
    WM_NULL
    [...]
    Remarks
    For example, if an application has installed a WH_GETMESSAGE hook and wants to prevent a message from being processed, the GetMsgProc callback function can change the message number to WM_NULL so the recipient will ignore it.

    As another example, an application can check if a window is responding to messages by sending the WM_NULL message with the SendMessageTimeout function.
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  3. #3
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    Re: Do you use WM_NULL?

    Originally posted by Alex Rest
    I have found funny windows message.
    .
    .
    .
    An application sends the WM_NULL message if it wants to post a message that the recipient window will ignore.
    I do not see anything funny about that. Just to give you few examples:

    This message is used to test if application is still responding and is not hang. Task manager does that by using SendMessageTimeout with WM_NULL.

    WM_NULL is also used to filter messages in WH_GETMESSAGE hook. Returning 0 from a hook does not prevent from processing a message. Replacing message with WM_NULL will filter message properly.

    Another use is ActiveX control when you decide that it has toolbar and tooltips. Normally application message pump calls PreTranslateMessage; since ActiveX control does not have one, message hook can call PreTranslateMessage and if handled replace original message with WM_NULL.
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  4. #4
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    O!
    I am agree.
    It is useful.
    Thanks for good examples.

  5. #5
    ovidiucucu's Avatar
    ovidiucucu is offline Moderator/Reviewer Power Poster
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    Hi Alex,

    Just joking...
    You were like a Java-fan wondering: "What is NULL good for???"


    Keep ahead!
    Ovidiu Cucu
    "When in Rome, do as Romans do."
    Visit: Microsoft Virtual Academy
    Follow: https://twitter.com/#!/ovidiucucu
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