c# - 将 NativeWindow 用于 ComboBox 会导致 Dispose 方法出现异常

Question

在 C# Windows.Forms 中，我想拦截组合框的粘贴窗口消息。因为这不能通过覆盖组合框的 WndProc 方法来工作，因为我需要覆盖组合框内文本框的 WndProc，所以我决定创建一个 NativeWindow 类型的自定义类来覆盖 WndProc。当组合框句柄被破坏时，我分配句柄并释放它。但是当组合框的 Dispose 被调用时，问题是我得到一个 InvalidOperationException 说发生了无效的跨线程操作，并且组合框是从创建它的线程以外的线程访问的。知道这里出了什么问题吗？

在下文中您将看到我的类的外观:

public class MyCustomComboBox : ComboBox
{
    private WinHook hook = null;

    public MyCustomComboBox()
        : base()
    {
        this.hook = new WinHook(this);
    }

    private class WinHook : NativeWindow
    {
        public WinHook(MyCustomComboBox parent)
        {
            parent.HandleCreated += new EventHandler(this.Parent_HandleCreated);
            parent.HandleDestroyed += new EventHandler(this.Parent_HandleDestroyed);
        }

        protected override void WndProc(ref Message m)
        {
            // do something

            base.WndProc(ref m);
        }

        private void Parent_HandleCreated(object sender, EventArgs e)
        {
            MyCustomComboBox cbx = (MyCustomComboBox)sender;

            this.AssignHandle(cbx.Handle);
        }

        private void Parent_HandleDestroyed(object sender, EventArgs e)
        {
            this.ReleaseHandle();
        }
    }
}

Answer 1

根据 Hans 的建议，我修改了代码以使用 CB_GETCOMBOBOXINFO来自他自己的一个例子。

public class PastelessComboBox : ComboBox {

    private class TextWindow : NativeWindow {
      [StructLayout(LayoutKind.Sequential)]
      private struct RECT {
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;
      }

      private struct COMBOBOXINFO {
        public Int32 cbSize;
        public RECT rcItem;
        public RECT rcButton;
        public int buttonState;
        public IntPtr hwndCombo;
        public IntPtr hwndEdit;
        public IntPtr hwndList;
      }

      [DllImport("user32.dll", EntryPoint = "SendMessageW", CharSet = CharSet.Unicode)]
      private static extern IntPtr SendMessageCb(IntPtr hWnd, int msg, IntPtr wp, out COMBOBOXINFO lp);

      public TextWindow(ComboBox cb) {
        COMBOBOXINFO info = new COMBOBOXINFO();
        info.cbSize = Marshal.SizeOf(info);
        SendMessageCb(cb.Handle, 0x164, IntPtr.Zero, out info);
        this.AssignHandle(info.hwndEdit);
      }

      protected override void WndProc(ref Message m) {
        if (m.Msg == (0x0302)) {
          MessageBox.Show("No pasting allowed!");
          return;
        }
        base.WndProc(ref m);
      }
    }

    private TextWindow textWindow;

    protected override void OnHandleCreated(EventArgs e) {
      textWindow = new TextWindow(this);
      base.OnHandleCreated(e);
    }

    protected override void OnHandleDestroyed(EventArgs e) {
      textWindow.ReleaseHandle();
      base.OnHandleDestroyed(e);
    }

  }