Default Trackbar Message Processing
This section describes the window message processing performed by a trackbar.
Message | Processing performed |
WM_CAPTURECHANGED | Kills the timer if one was set during WM_LBUTTONDOWN processing and sends the TB_THUMBPOSITION notification message, if necessary. It always sends the TB_ENDTRACK notification message. |
WM_CREATE | Performs additional initialization. It sets the initial tick frequency to 1, the line size to 1, and the page size to - 1. |
WM_DESTROY | Frees resources. |
WM_ENABLE | Repaints the trackbar window. |
WM_ERASEBKGND | Erases the window background, using the current background color for the trackbar. |
WM_GETDLGCODE | Returns the DLGC_WANTARROWS value. |
WM_KEYDOWN | Processes the direction keys and sends the TB_TOP, TB_BOTTOM, TB_PAGEUP, TB_PAGEDOWN, TB_LINEUP, and TB_LINEDOWN notification messages, as appropriate. |
WM_KEYUP | Sends the TB_ENDTRACK notification message if the key was one of the direction keys. |
WM_KILLFOCUS | Repaints the trackbar window. |
WM_LBUTTONDOWN | Sets the focus and the mouse capture to the trackbar. When necessary, it sets a timer that determines how quickly the slider moves toward the mouse cursor when the user holds down the mouse button in the window. |
WM_LBUTTONUP | Releases the mouse capture and kills the timer if one was set during WM_LBUTTONDOWN processing. It sends the TB_THUMBPOSITION notification message, if necessary. It always sends the TB_ENDTRACK notification message. |
WM_MOUSEMOVE | Moves the slider and sends the TB_THUMBTRACK notification message when tracking the mouse (see WM_TIMER). |
WM_PAINT | Paints the trackbar. If the wParam parameter is non-NULL, the control assumes that the value is an HDC and paints using that device context. |
WM_SETFOCUS | Repaints the trackbar window. |
WM_SIZE | Sets the dimensions of the trackbar, removing the slider if there is not enough room to display it. |
WM_TIMER | Retrieves the mouse position and updates the position of the slider. (It is received only when the user is dragging the slider.) |
WM_WININICHANGE | Initializes slider dimensions. |