Cómo: Utilizar una clase para enlazar procedimientos de Windows
Actualización: noviembre 2007
Este programa de ejemplo asigna un procedimiento de ventana, WndProc, a una ventana cuando recibe un mensaje de Windows determinado. Esta acción tiene lugar cuando el identificador de la ventana, hwnd, se asigna a identificadores de la colección para responder cuando se recibe ese mensaje de Windows. Los temas "Cómo..." siguientes utilizan esta clase:
Cómo: Crear subclases de un control TreeView mediante devoluciones de llamada nativas
Cómo: Crear subclases de un botón mediante devoluciones de llamada nativas
Este programa de ejemplo se describe con detalle en Crear subclases de controles con un procedimiento de ventana administrado.
Ejemplo
public class WndProcHooker
{
// The WndProcCallback method is used when a hooked
// window's message map contains the hooked message.
// Parameters:
// hwnd - The handle to the window for which the message
// was received.
// wParam - The message's parameters (part 1).
// lParam - The message's parameters (part 2).
// handled - The invoked function sets this to true if it
// handled the message. If the value is false when the callback
// returns, the next window procedure in the wndproc chain is
// called.
//
// Returns a value specified for the given message.
public delegate int WndProcCallback(
IntPtr hwnd, uint msg, uint wParam, int lParam, ref bool handled);
// This is the global list of all the window procedures we have
// hooked. The key is an hwnd. The value is a HookedProcInformation
// object which contains a pointer to the old wndproc and a map of
// message's callbacks for the window specified. Controls whose handles
// have been created go into this dictionary.
private static Dictionary<IntPtr, HookedProcInformation> hwndDict =
new Dictionary<IntPtr, HookedProcInformation>();
// The key for this dictionary is a control and the value is a
// HookedProcInformation. Controls whose handles have not been created
// go into this dictionary. When the HandleCreated event for the
// control is fired the control is moved into hwndDict.
private static Dictionary<Control, HookedProcInformation> ctlDict =
new Dictionary<Control, HookedProcInformation>();
// Makes a connection between a message on a specified window handle
// and the callback to be called when that message is received. If the
// window was not previously hooked it is added to the global list of
// all the window procedures hooked.
// Parameters:
// ctl - The control whose wndproc we are hooking.
// callback - The method to call when the specified.
// message is received for the specified window.
// msg - The message being hooked.
public static void HookWndProc(
Control ctl, WndProcCallback callback, uint msg)
{
HookedProcInformation hpi = null;
if (ctlDict.ContainsKey(ctl))
hpi = ctlDict[ctl];
else if (hwndDict.ContainsKey(ctl.Handle))
hpi = hwndDict[ctl.Handle];
if (hpi == null)
{
// If new control, create a new
// HookedProcInformation for it.
hpi = new HookedProcInformation(ctl,
new Win32.WndProc(WndProcHooker.WindowProc));
ctl.HandleCreated += new EventHandler(ctl_HandleCreated);
ctl.HandleDestroyed += new EventHandler(ctl_HandleDestroyed);
ctl.Disposed += new EventHandler(ctl_Disposed);
// If the handle has already been created set the hook. If it
// hasn't been created yet, the hook will get set in the
// ctl_HandleCreated event handler.
if (ctl.Handle != IntPtr.Zero)
hpi.SetHook();
}
// Stick hpi into the correct dictionary.
if (ctl.Handle == IntPtr.Zero)
ctlDict[ctl] = hpi;
else
hwndDict[ctl.Handle] = hpi;
// Add the message/callback into the message map.
hpi.messageMap[msg] = callback;
}
// The event handler called when a control is disposed.
static void ctl_Disposed(object sender, EventArgs e)
{
Control ctl = sender as Control;
if (ctlDict.ContainsKey(ctl))
ctlDict.Remove(ctl);
else
System.Diagnostics.Debug.Assert(false);
}
// The event handler called when a control's handle is destroyed.
// We remove the HookedProcInformation from hwndDict and
// put it back into ctlDict in case the control get re-
// created and we still want to hook its messages.
static void ctl_HandleDestroyed(object sender, EventArgs e)
{
// When the handle for a control is destroyed, we want to
// unhook its wndproc and update our lists
Control ctl = sender as Control;
if (hwndDict.ContainsKey(ctl.Handle))
{
HookedProcInformation hpi = hwndDict[ctl.Handle];
UnhookWndProc(ctl, false);
}
else
System.Diagnostics.Debug.Assert(false);
}
// The event handler called when a control's handle is created. We
// call SetHook() on the associated HookedProcInformation object and
// move it from ctlDict to hwndDict.
static void ctl_HandleCreated(object sender, EventArgs e)
{
Control ctl = sender as Control;
if (ctlDict.ContainsKey(ctl))
{
HookedProcInformation hpi = ctlDict[ctl];
hwndDict[ctl.Handle] = hpi;
ctlDict.Remove(ctl);
hpi.SetHook();
}
else
System.Diagnostics.Debug.Assert(false);
}
// This is a generic wndproc. It is the callback for all hooked
// windows. If we get into this function, we look up the hwnd in the
// global list of all hooked windows to get its message map. If the
// message received is present in the message map, its callback is
// invoked with the parameters listed here.
// Parameters:
// hwnd - The handle to the window that received the
// message
// msg - The message
// wParam - The message's parameters (part 1)
// lParam - The messages's parameters (part 2)
// Returns the callback handled the message, the callback's return
// value is returned form this function. If the callback didn't handle
// the message, the message is forwarded on to the previous wndproc.
private static int WindowProc(
IntPtr hwnd, uint msg, uint wParam, int lParam)
{
if (hwndDict.ContainsKey(hwnd))
{
HookedProcInformation hpi = hwndDict[hwnd];
if (hpi.messageMap.ContainsKey(msg))
{
WndProcCallback callback = hpi.messageMap[msg];
bool handled = false;
int retval = callback(hwnd, msg, wParam, lParam, ref handled);
if (handled)
return retval;
}
// If the callback didn't set the handled property to true,
// call the original window procedure.
return hpi.CallOldWindowProc(hwnd, msg, wParam, lParam);
}
System.Diagnostics.Debug.Assert(
false, "WindowProc called for hwnd we don't know about");
return Win32.DefWindowProc(hwnd, msg, wParam, lParam);
}
// This method removes the specified message from the message map for
// the specified hwnd.
public static void UnhookWndProc(Control ctl, uint msg)
{
// Look for the HookedProcInformation in the
// ctrDict and hwndDict dictionaries.
HookedProcInformation hpi = null;
if (ctlDict.ContainsKey(ctl))
hpi = ctlDict[ctl];
else if (hwndDict.ContainsKey(ctl.Handle))
hpi = hwndDict[ctl.Handle];
// if we couldn't find a HookedProcInformation, throw
if (hpi == null)
throw new ArgumentException("No hook exists for this control");
// look for the message we are removing in the messageMap
if (hpi.messageMap.ContainsKey(msg))
hpi.messageMap.Remove(msg);
else
// if we couldn't find the message, throw
throw new ArgumentException(
string.Format(
"No hook exists for message ({0}) on this control",
msg));
}
// Restores the previous wndproc for the specified window.
// Parameters:
// ctl - The control whose wndproc we no longer want to hook.
// disposing - True if HookedProcInformation is not
// read back into ctlDict.
public static void UnhookWndProc(Control ctl, bool disposing)
{
HookedProcInformation hpi = null;
if (ctlDict.ContainsKey(ctl))
hpi = ctlDict[ctl];
else if (hwndDict.ContainsKey(ctl.Handle))
hpi = hwndDict[ctl.Handle];
if (hpi == null)
throw new ArgumentException("No hook exists for this control");
// If we found our HookedProcInformation in ctlDict and we are
// disposing remove it from ctlDict.
if (ctlDict.ContainsKey(ctl) && disposing)
ctlDict.Remove(ctl);
// If we found our HookedProcInformation in hwndDict, remove it
// and if we are not disposing stick it in ctlDict.
if (hwndDict.ContainsKey(ctl.Handle))
{
hpi.Unhook();
hwndDict.Remove(ctl.Handle);
if (!disposing)
ctlDict[ctl] = hpi;
}
}
// This class remembers the old window procedure for the specified
// window handle and also provides the message map for the messages
// hooked on that window.
class HookedProcInformation
{
// The message map for the window.
public Dictionary<uint, WndProcCallback> messageMap;
// The old window procedure for the window.
private IntPtr oldWndProc;
// The delegate that gets called in place of this window's
// wndproc.
private Win32.WndProc newWndProc;
// Control whose wndproc is being hooked.
private Control control;
// Constructs a new HookedProcInformation object
// Parameters:
// ctl - The handle to the window being hooked
// wndproc - The window procedure to replace the
// original one for the control.
public HookedProcInformation(Control ctl, Win32.WndProc wndproc)
{
control = ctl;
newWndProc = wndproc;
messageMap = new Dictionary<uint, WndProcCallback>();
}
// Replaces the windows procedure for control with the
// one specified in the constructor.
public void SetHook()
{
IntPtr hwnd = control.Handle;
if (hwnd == IntPtr.Zero)
throw new InvalidOperationException(
"Handle for control has not been created");
oldWndProc = Win32.SetWindowLong(hwnd, Win32.GWL_WNDPROC,
Marshal.GetFunctionPointerForDelegate(newWndProc));
}
// Restores the original window procedure for the control.
public void Unhook()
{
IntPtr hwnd = control.Handle;
if (hwnd == IntPtr.Zero)
throw new InvalidOperationException(
"Handle for control has not been created");
Win32.SetWindowLong(hwnd, Win32.GWL_WNDPROC, oldWndProc);
}
// Calls the original window procedure of the control with the
// arguments provided.
// Parameters:
// hwnd - The handle of the window that received the
// message
// msg - The message
// wParam - The message's arguments (part 1)
// lParam - The message's arguments (part 2)
// Returns the value returned by the control's original wndproc.
public int CallOldWindowProc(
IntPtr hwnd, uint msg, uint wParam, int lParam)
{
return Win32.CallWindowProc(
oldWndProc, hwnd, msg, wParam, lParam);
}
}
}
Vea también
Tareas
Cómo: Usar una clase auxiliar para las invocaciones de la plataforma
Cómo: Crear subclases de un control TreeView mediante devoluciones de llamada nativas
Cómo: Crear subclases de un botón mediante devoluciones de llamada nativas
Conceptos
Crear subclases de controles con un procedimiento de ventana administrado
.Temas "Cómo..." de .NET Compact Framework