Input Context

An input context is an internal structure, maintained by the IME, that contains information about the status of the IME and is used by IME windows. By default, the system creates and assigns an input context to each thread. Within the thread, this default input context is a shared resource and is associated with each newly created window.

To retrieve or set information in the IME, an application must first retrieve a handle to the input context associated with a specified window. You retrieve the handle by using the ImmGetContext function. You can use the retrieved handle in subsequent calls to the input method manager functions to retrieve and set IME values, such as the composition window style, the composition style, and the status window position. Once you have finished using the context, you must release it using the ImmReleaseContext function.

Because the default input context is a shared resource, any changes you make to it apply to all windows in the thread. However, you can override this default behavior by creating and associating your own input context to one or more windows of the thread. The changes you make to your own input context apply only to the windows with which it is associated.

You can create an input context by using the ImmCreateContext function. To assign the context to a window, call the ImmAssociateContext function. This function returns a handle to the previously associated input context. If you have not associated an input context with the window before, the returned handle is for the default input context. Typically, you save this handle and later reassociate it with the window when you no longer want to use your own input context.

Once an input context is associated with a window, the system automatically selects that context when the window is activated and receives the input focus. The style and other information in the input context affects subsequent keyboard input for that window, determining whether and how the IME operates.

You must destroy any input context you create before terminating your application. First, you must remove the input context from any association it has with windows in the thread by using the ImmAssociateContext function. Then, call the ImmDestroyContext function.