windows - 同步使用 GetWindowText

Question

我不太明白 GetWindowText 如何在与调用者相同的线程上为窗口工作。如果 GetWindowText 阻塞直到消息被处理，线程如何调用 DispatchMessage？它已在 GetWindowText 中被阻止。这是否意味着 GetWindowText 必须始终从与操作消息循环的线程不同的线程调用？

Answer 1

GetWindowText 只是 SendMessage(WM_GETTEXT) 的薄包装。

发送到窗口的消息总是在创建窗口的线程中处理(窗口具有“线程关联”)。发送消息不经过DispatchMessage，而是GetMessage(或PeekMessage或MsgWaitForMultipleObjects)直接调用窗口过程, 对于从另一个线程发送的消息。如果消息是从同一个线程发送的，SendMessage 将调用窗口过程。

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SendMessage documentation说:

The SendMessage function calls the window procedure for the specified window and does not return until the window procedure has processed the message.

和the GetMessage documentation says :

Retrieves a message from the calling thread's message queue. The function dispatches incoming sent messages until a posted message is available for retrieval.

来自 the PeekMessage docs :

Dispatches incoming sent messages, checks the thread message queue for a posted message, and retrieves the message (if any exist).

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发送消息的行为之前已经在Raymond Chen's excellent blog, The Old New Thing上高亮显示了，所有 Win32 开发人员都应该订阅:

If you use any of the above send-type functions to send a message to a window that belongs to the sending thread, the call is made synchronously.

• http://blogs.msdn.com/b/oldnewthing/archive/2004/11/19/266664.aspx

Recall that SendMessage delivers the message directly to the window procedure; the message pump never sees it.

• http://blogs.msdn.com/b/oldnewthing/archive/2008/12/23/9248851.aspx

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当然，在 StackOverflow 上可以找到相关问题:

• SendMessage vs PostMessage + WaitForSingleObject