windows_programming_notes.nbk: Home | Index | Next Page: WM_LBUTTONDOWN | Previous Page: WM_KILLFOCUS

 WM_LBUTTONDBLCLK

The WM_LBUTTONDBLCLK message is posted when the user double-clicks the left mouse button while the cursor is in the client area of a window. If the mouse is not captured, the message is posted to the window beneath the cursor. Otherwise, the message is posted to the window that has captured the mouse.

A window receives this message through its WindowProc function.

    LRESULT CALLBACK WindowProc(
      HWND hwnd,       // handle to window
      UINT uMsg,       // WM_LBUTTONDBLCLK
      WPARAM wParam,   // key indicator
      LPARAM lParam    // horizontal and vertical position
    );

Parameters

• wParam
  Indicates whether various virtual keys are down. This parameter can be one or more of the following values. Value Description
  MK_CONTROL The CTRL key is down. MK_LBUTTON The left mouse button is down. MK_MBUTTON The middle mouse button is down. MK_RBUTTON The right mouse button is down. MK_SHIFT The SHIFT key is down. MK_XBUTTON1 Windows 2000 or later: The first X button is down. MK_XBUTTON2 Windows 2000 or later: The second X button is down.
• lParam
  • The low-order word specifies the x-coordinate of the cursor. The coordinate is relative to the upper-left corner of the client area.
  • The high-order word specifies the y-coordinate of the cursor. The coordinate is relative to the upper-left corner of the client area.

Return Values

If an application processes this message, it should return zero.

Remarks

Use the following code to obtain the horizontal and vertical position:

xPos = GET_X_LPARAM(lParam); yPos = GET_Y_LPARAM(lParam); You can also use the MAKEPOINTS macro to convert the lParam parameter to a POINTS structure.

Only windows that have the CS_DBLCLKS style can receive WM_LBUTTONDBLCLK messages, which the system generates whenever the user presses, releases, and again presses the left mouse button within the system's double-click time limit. Double-clicking the left mouse button actually generates a sequence of four messages: WM_LBUTTONDOWN, WM_LBUTTONUP, WM_LBUTTONDBLCLK, and WM_LBUTTONUP.

Requirements

  Windows NT/2000 or later: Requires Windows NT 3.1 or later.
  Windows 95/98/Me: Requires Windows 95 or later.
  Header: Declared in Winuser.h; include Windows.h.

Prototype for Message Handler

void on_lbutton_dbl_clk(HWND hwnd, BOOL doubleclick, int x, int y, UINT
keyflags)
{
}

#define HANDLE_WM_LBUTTONDBLCLK(hwnd,wParam,lParam,fn) 
((fn)((hwnd),TRUE,(int)(short)LOWORD(lParam),(int)(short)HIWORD(lParam),(UINT)(wParam)),0)

args to handler:

• handle of window
• TRUE
• loword of lParam
• hiword of lParam
• wParam

windows_programming_notes.nbk: Home | Index | Next Page: WM_LBUTTONDOWN | Previous Page: WM_KILLFOCUS

Notebook exported on Monday, 7 July 2008, 18:56:50 PM Eastern Daylight Time