附加参数有时候很有用。
比如：
WM_SETICON
An application sends the WM_SETICON message to associate a new large or small icon with a window. The system displays the large icon in the ALT+TAB dialog box, and the small icon in the window caption.
To send this message, call the SendMessage function with the following parameters.
SendMessage( (HWND) hWnd, // handle to destination window WM_SETICON, // message to send (WPARAM) wParam, // icon type (LPARAM) lParam // handle to icon (HICON));
Parameters
- wParam
- Specifies the type of icon to be set. This parameter can be one of the following values.
Value Meaning ICON_BIG Set the large icon for the window. ICON_SMALL Set the small icon for the window. - lParam
- Handle to the new large or small icon. If this parameter is NULL, the icon indicated by wParam is removed.
Return Values
The return value is a handle to the previous large or small icon, depending on the value of wParam. It is NULL if the window previously had no icon of the type indicated by wParam.