| Platform SDK: Win32 API |
When an application with subsystem version 4.0 uses the SetWindowLong function to change a window's style, Windows 95/98 sends the window a WM_STYLECHANGING message before changing the style. The message's lParam parameter is the address of a STYLESTRUCT structure. The styleOld and styleNew members of the structure specify the old and new styles. By processing WM_STYLECHANGING, an application can inspect the styles and perhaps change them.
Windows 95/98 sends the WM_STYLECHANGED message after changing the style. Again, the lParam parameter is the address of a STYLESTRUCT structure that specifies the new styles. The application can use WM_STYLECHANGED to update any style-dependent information stored in the application's internal data structures.
Windows 95/98, however, does not send the WM_STYLECHANGING and WM_STYLECHANGED messages to a version 3.x application.
An application marked version 4.0 cannot use the SetWindowLong function to set the WS_EX_TOPMOST style for a window or to remove the style from a window. The application must use the SetWindowPos function to set or remove the WS_EX_TOPMOST style.
Windows 95/98 automatically adds and removes the WS_EX_WINDOWEDGE style for windows in both version 3.x and 4.0 applications. For a version 3.x application, Windows 95/98 adds the WS_EX_WINDOWEDGE style to a window if, in version 3.1, the window would have a dialog border or a sizable border. Windows 95/98 removes the WS_EX_WINDOWEDGE style if the window's style changes so that it would no longer have a dialog border or sizable border in version 3.1. Windows 95/98 uses similar criteria for adding and removing the WS_EX_WINDOWEDGE style for a version 4.0 application, except that any window that has a title bar receives the WS_EX_WINDOWEDGE style, regardless of the window's other border styles.
When the user drags the icon of a minimized window created by a version 3.x application, Windows 95/98 sends the window a WM_QUERYDRAGICON message to retrieve the cursor to use while dragging. Windows 95/98 also sends WM_QUERYDRAGICON to retrieve the icon to display in the task-switch window that appears when the user presses the ALT+TAB key combination. Windows 95/98 does not send WM_QUERYDRAGICON to a window created by a version 4.0 application. Instead, the application is expected either to use the WM_SETICON and WM_GETICON messages or to set the big and small icons when registering the window class.
When a window in a version 4.0 application loses the mouse capture as a result of a call to the SetCapture function, the window receives a WM_CAPTURECHANGED message, but Windows 95/98 sends the message asynchronously. In other words, the window receives the message, but possibly not right away. Some of the ways in which a window can lose the mouse capture include:
If a child window in a version 3.x application has the WS_EX_NOPARENTNOTIFY style, Windows 95/98 disregards the style when the user clicks the child window. That is, Windows 95/98 sends the WM_PARENTNOTIFY message to all windows in the parent chain regardless of whether the child window has the WS_EX_NOPARENTNOTIFY style. If a child window in a version 4.0 application has this style, Windows 95/98 does not send WM_PARENTNOTIFY messages when the user clicks the child window.
In a version 3.x application, it is possible for the horizontal coordinate on the left side of a window's client area to be greater than that on the right side. This happens because version 3.x sometimes incorrectly handles an empty client rectangle that contains a vertical scroll bar. (Fixing the problem would cause some applications to generate general protection faults.) In a version 4.0 application, it is not possible for the horizontal coordinate of the left side of a client area to be greater than that of the right side.