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AttachThreadInput

Posted on 1998-01-14
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Last Modified: 2013-12-03
Hello,

What is the purpose of AttachThreadInput ??????
How can I use it

Andrew
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Question by:andrewyu
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alexo earned 0 total points
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Quoting several documents:

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Windows created in different threads typically process input independently of each other. That is, they have their own input states (focus, active, capture windows, key state, queue status, and so on), and they are not synchronized with the input processing of other threads. By using the AttachThreadInput function, a thread can attach its input processing to another thread. This also allows threads to share their input states, so they can call the SetFocus function to set the keyboard focus to a window of a different thread. This also allows threads to get key-state information. These capabilities are not generally possible.
The AttachThreadInput function fails if either of the specified threads does not have a message queue. The system creates a thread's message queue when the thread makes its first call to one of the Win32 USER or GDI functions. The AttachThreadInput function also fails if a journal record hook is installed. Journal record hooks attach all input queues together.
Note that key state, which can be ascertained by calls to the GetKeyState or GetKeyboardState function, is reset after a call to AttachThreadInput.

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Normally, windows created in different threads process input independently of each other. The windows have their own input states and the threads are not synchronized with eachother in regards to input processing.

In order to have threads to share input state, have one thread call AttachThreadInput() to have its input processing attached to another thread. What this means is that these two threads will use a Windows 3.1 style system queue. The threads will still have separate input, but they will take turns reading out of the same queue.

Creating a window can force an implicit AttachThreadInput(), when a parent window is created in one thread and the child window is being created in another thread. When windows are created (or set) in separate threads with a parent-child relationship, the input queues are attached.

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By default, each thread has an independent input state (its own active window, its own focus window, and so forth). SetActiveWindow() always logically sets a thread's active window state. To force a window to the foreground, however, use SetForegroundWindow(). SetForegroundWindow() activates a window and forces the window into the foreground.
SetActiveWindow() always activates, but it brings the active window into the foreground only if the thread is the foreground thread.

NOTE: If the target window was not created by the calling thread, the active window status of the calling thread is set to NULL, and the active window status of the thread that created the target window is set to the target window.

Applications can call AttachThreadInput() to allow a set of threads to share the same input state. By sharing input state, the threads share their concept of the active window. By doing this, one thread can always activate another thread's window. This function is also useful for sharing focus state, mouse capture state, keyboard state, and window Z-order state among windows created by different threads whose input state is shared.

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The AttachThreadInput function can be used to allow a set of threads to share the same input state. By sharing input state, the threads share their concept of the active window. By doing this, one thread can always activate another thread's window. This function is also useful for sharing focus state, mouse capture state, keyboard state, and window Z-order state among windows created by different threads whose input state is shared.

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