RegisterMessage

Subscribes a callback to a single Windows message type for a chosen window and descendant scope.

Syntax: hook.RegisterMessage ParentHWND , Mode , MessageType , Callback

hook
required An IGetMessageHook instance, typically returned by RuntimeCreateGetMessageHook.
ParentHWND
required LongPtr. The window the subscription anchors on.
Mode
required EnumDescendantsModeFlags. The descendant scope: only the exact window, all descendants, or only direct children.
MessageType
required Integer. The Windows WM_* message identifier to subscribe to. Each call subscribes to one type; call RegisterMessage repeatedly to listen for several.
Callback
required GetMessageHookHelper.GetMessageHandler. The function that receives matching messages. Pass AddressOf a function with the matching signature.

The subscription is recorded but does not start firing until Start is called on the hook. Existing subscriptions are not disturbed by adding new ones.

Example 

Const WM_KEYDOWN = &H100
Const WM_CHAR = &H102

Sub HookKeyboard(ByVal h As IGetMessageHook)
    h.RegisterMessage Me.hWnd, AllDescendants, WM_KEYDOWN, AddressOf OnKeyDown
    h.RegisterMessage Me.hWnd, AllDescendants, WM_CHAR,    AddressOf OnChar
    h.Start
End Sub

See Also