ShellProc function


An application-defined or library-defined callback function used with the SetWindowsHookExA/SetWindowsHookExW function. The function receives notifications of Shell events from the system.

The HOOKPROC type defines a pointer to this callback function. ShellProc is a placeholder for the application-defined or library-defined function name.

  _In_ int    nCode,
  _In_ WPARAM wParam,
  _In_ LPARAM lParam


nCode [in]

Type: int

The hook code.

If nCode is less than zero, the hook procedure must pass the message to the CallNextHookEx function without further processing and should return the value returned by CallNextHookEx.

This parameter can be one of the following values.

Value Meaning
HSHELL_ACCESSIBILITYSTATE 11 The accessibility state has changed.
HSHELL_ACTIVATESHELLWINDOW 3 The shell should activate its main window.
HSHELL_APPCOMMAND 12 The user completed an input event (for example, pressed an application command button on the mouse or an application command key on the keyboard), and the application did not handle the WM_APPCOMMAND message generated by that input. If the Shell procedure handles the WM_COMMAND message, it should not call CallNextHookEx. See the Return Value section for more information.
HSHELL_GETMINRECT 5 A window is being minimized or maximized. The system needs the coordinates of the minimized rectangle for the window.
HSHELL_LANGUAGE 8 Keyboard language was changed or a new keyboard layout was loaded.
HSHELL_REDRAW 6 The title of a window in the task bar has been redrawn.
HSHELL_TASKMAN 7 The user has selected the task list. A shell application that provides a task list should return TRUE to prevent Windows from starting its task list.
HSHELL_WINDOWACTIVATED 4 The activation has changed to a different top-level, unowned window.
HSHELL_WINDOWCREATED 1 A top-level, unowned window has been created. The window exists when the system calls this hook.
HSHELL_WINDOWDESTROYED 2 A top-level, unowned window is about to be destroyed. The window still exists when the system calls this hook.
HSHELL_WINDOWREPLACED 13 A top-level window is being replaced. The window exists when the system calls this hook.

wParam [in]


This parameter depends on the value of the nCode parameter, as shown in the following table.

nCode wParam
HSHELL_ACCESSIBILITYSTATE Indicates which accessibility feature has changed state. This value is one of the following: ACCESS_FILTERKEYS, ACCESS_MOUSEKEYS, or ACCESS_STICKYKEYS.
HSHELL_APPCOMMAND Indicates where the WM_APPCOMMAND message was originally sent; for example, the handle to a window. For more information, see cmd parameter in WM_APPCOMMAND.
HSHELL_GETMINRECT A handle to the minimized or maximized window.
HSHELL_LANGUAGE A handle to the window.
HSHELL_REDRAW A handle to the redrawn window.
HSHELL_WINDOWACTIVATED A handle to the activated window.
HSHELL_WINDOWCREATED A handle to the created window.
HSHELL_WINDOWDESTROYED A handle to the destroyed window.
HSHELL_WINDOWREPLACED A handle to the window being replaced. Windows 2000: Not supported.

lParam [in]


This parameter depends on the value of the nCode parameter, as shown in the following table.

nCode lParam
HSHELL_APPCOMMAND GET_APPCOMMAND_LPARAM(lParam) is the application command corresponding to the input event. GET_DEVICE_LPARAM(lParam) indicates what generated the input event; for example, the mouse or keyboard. For more information, see the uDevice parameter description under WM_APPCOMMAND. GET_FLAGS_LPARAM(lParam) depends on the value of cmd in WM_APPCOMMAND. For example, it might indicate which virtual keys were held down when the WM_APPCOMMAND message was originally sent. For more information, see the dwCmdFlags description parameter under WM_APPCOMMAND.
HSHELL_GETMINRECT A pointer to a RECT structure.
HSHELL_LANGUAGE A handle to a keyboard layout.
HSHELL_MONITORCHANGED A handle to the window that moved to a different monitor.
HSHELL_REDRAW The value is TRUE if the window is flashing, or FALSE otherwise.
HSHELL_WINDOWACTIVATED The value is TRUE if the window is in full-screen mode, or FALSE otherwise.
HSHELL_WINDOWREPLACED A handle to the new window. Windows 2000: Not supported.



The return value should be zero unless the value of nCode is HSHELL_APPCOMMAND and the shell procedure handles the WM_COMMAND message. In this case, the return should be nonzero.


Install this hook procedure by specifying the WH_SHELL hook type and a pointer to the hook procedure in a call to the SetWindowsHookEx function.

See also