How to enable IME on a custom UserControl? - .NET

"By default, the system associates the input context maintained by the
default IME with each window, i.e. a control on a form, as it is created.

When a window is activated or gets focused, the system sends the
WM_IME_SETCONTENT message to the application. Then the application sends
this message to the default IME window.

Note that at this time, those controls that don't require text input, e.g.
Button, UserControl, Panel and so on, will remove the association to the
default input context from themselves. So, the the default IME is disabled.
In order to enable the IME on a custom UserControl, we could call the input
method manager (IMM) function 'ImmAssociateContext' to associate the
default input context to the custom UserControl at this time."