c#关于钩子的消息放行问题，返回值为0但是还不放行消息。

Question

    private int KeyboardHookProc(int nCode, Int32 wParam, IntPtr lParam)
    {
        // 侦听键盘事件
        if ((nCode >= 0) && (KeyDownEvent != null || KeyUpEvent != null || KeyPressEvent != null))
        {
            KeyboardHookStruct MyKeyboardHookStruct = (KeyboardHookStruct)Marshal.PtrToStructure(lParam, typeof(KeyboardHookStruct));
            // raise KeyDown
            if (KeyDownEvent != null && (wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN))
            {
                Keys keyData = (Keys)MyKeyboardHookStruct.vkCode;
                System.Windows.Forms.KeyEventArgs e = new System.Windows.Forms.KeyEventArgs(keyData);
                KeyDownEvent(this, e);
            }

            //键盘按下
            if (KeyPressEvent != null && wParam == WM_KEYDOWN)
            {
                byte[] keyState = new byte[256];
                GetKeyboardState(keyState);

                byte[] inBuffer = new byte[2];
                if (ToAscii(MyKeyboardHookStruct.vkCode, MyKeyboardHookStruct.scanCode, keyState, inBuffer, MyKeyboardHookStruct.flags) == 1)
                {
                    KeyPressEventArgs e = new KeyPressEventArgs((char)inBuffer[0]);
                    KeyPressEvent(this, e);
                }
            }

            // 键盘抬起
            if (KeyUpEvent != null && (wParam == WM_KEYUP || wParam == WM_SYSKEYUP))
            {
                Keys keyData = (Keys)MyKeyboardHookStruct.vkCode;
                System.Windows.Forms.KeyEventArgs e = new System.Windows.Forms.KeyEventArgs(keyData);
                KeyUpEvent(this, e);
            }

        }
        //如果返回1，则结束消息，这个消息到此为止，不再传递。
        //如果返回0或调用CallNextHookEx函数则消息出了这个钩子继续往下传递，也就是传给消息真正的接受者
        //return CallNextHookEx(hKeyboardHook, nCode, wParam, lParam);

        return 0;
    }


                消息不放行，拦截消息后其他的程序就得不到消息了。