/// <summary>
/// Subclasses the window.
/// </summary>
/// <remarks>
/// You must call <see cref="Dispose()"/> to undo the subclassing before
/// the window is destroyed.
/// </remarks>
/// <returns></returns>
public void Open()
{
if (_disposed)
{
throw new ObjectDisposedException(nameof(WindowSubclassHandler));
}
if (_opened)
{
throw new InvalidOperationException();
}
// Replace the existing window procedure with our one
// ("instance subclassing").
// We need to explicitely clear the last Win32 error and then retrieve
// it, to check if the call succeeded.
WindowSubclassHandlerNativeMethods.SetLastError(0);
_originalWindowProc = WindowSubclassHandlerNativeMethods.SetWindowLongPtr(
_handle,
WindowSubclassHandlerNativeMethods.GWLP_WNDPROC,
_windowProcDelegatePtr);
if (_originalWindowProc == IntPtr.Zero && Marshal.GetLastWin32Error() != 0)
{
throw new Win32Exception();
}
Debug.Assert(_originalWindowProc != _windowProcDelegatePtr);
_opened = true;
}
protected virtual void Dispose(bool disposing)
{
if (!_disposed)
{
// We cannot do anything from the finalizer thread since we have
// resoures that must only be accessed from the GUI thread.
if (disposing && _opened)
{
// Check if the current window procedure is the correct one.
// We need to explicitely clear the last Win32 error and then
// retrieve it, to check if the call succeeded.
WindowSubclassHandlerNativeMethods.SetLastError(0);
IntPtr currentWindowProcedure = WindowSubclassHandlerNativeMethods.GetWindowLongPtr(
_handle,
WindowSubclassHandlerNativeMethods.GWLP_WNDPROC);
if (currentWindowProcedure == IntPtr.Zero && Marshal.GetLastWin32Error() != 0)
{
throw new Win32Exception();
}
if (currentWindowProcedure != _windowProcDelegatePtr)
{
throw new InvalidOperationException(
"The current window procedure is not the expected one.");
}
// Undo the subclassing by restoring the original window
// procedure.
WindowSubclassHandlerNativeMethods.SetLastError(0);
if (WindowSubclassHandlerNativeMethods.SetWindowLongPtr(
_handle,
WindowSubclassHandlerNativeMethods.GWLP_WNDPROC,
_originalWindowProc) == IntPtr.Zero &&
Marshal.GetLastWin32Error() != 0)
{
throw new Win32Exception();
}
// Ensure to keep the delegate alive up to the point after we
// have undone the subclassing.
KeepCallbackDelegateAlive();
}
_disposed = true;
}
}