[英]Use of NativeWindow for ComboBox causes exception in Dispose-method
In C# Windows.Forms I want to intercept the paste-windowmessage for a combobox. 在C#Windows.Forms中,我想截取一个组合框的paste-windowmessage。 As this doesn't work by overriding the WndProc-method of the combobox, because I would need to override the WndProc of the textbox inside the combobox, I decided to create a custom class of type NativeWindow which overrides the WndProc.
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,我决定创建一个类型为NativeWindow的自定义类,它会覆盖WndProc。 I assign the handle and release it, when the combobox-handle gets destroyed.
当组合框处理被破坏时,我分配句柄并释放它。 But when Dispose for the combobox is called the problem is that I get an InvalidOperationException saying that an invalid cross-thread operation occured and that the combobox was accessed from a thread other than the thread it was created on.
但是当调用组合框的Dispose时,问题是我得到一个InvalidOperationException,表示发生了无效的跨线程操作,并且组件框是从其创建的线程以外的线程访问的。 Any ideas what is going wrong here?
任何想法在这里出了什么问题?
In the following you'll see, how my classes look like: 在下面你将看到我的课程如何:
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();
}
}
}
Per Hans' suggestion, I modified the code to use CB_GETCOMBOBOXINFO from one of his own examples. 根据汉斯的建议,我修改了代码, 以便从他自己的一个例子中使用CB_GETCOMBOBOXINFO 。
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);
}
}
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