在GUI中，如果你使用了模态窗口，并且想从模态窗口中暂时中断，回到主窗口进行一些交互操作，然后再继续模态窗口中的任务，该如何操作？典型的就是 modal progress bar。也许你第一个会想到把窗口 Hide，
modalForm.Hide();
while(...) //等待主窗口的交互结果
{
while(...) //等待主窗口的交互结果
{
...
Application.DoEvent();
}
modalForm.ShowDialog(); //Continue
结果可能会让你失望，modalForm是Hide 了，但焦点却无论如何不能回到主窗口了。
我们可以通过win32的API 将焦点重新设到主窗口。首先要得到modalForm 的Handle，当然这个也可用win32 API。
/// <summary>
/// The FindWindow function retrieves the handle to the top-level window whose class name and window name match the specified strings.
/// This function does not search child windows.
/// </summary>
[DllImport("user32.dll", SetLastError = true)]
public static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);
/// The FindWindow function retrieves the handle to the top-level window whose class name and window name match the specified strings.
/// This function does not search child windows.
/// </summary>
[DllImport("user32.dll", SetLastError = true)]
public static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);
1 string progressBarText = "ModelDialog";
2 IntPtr progressBar =Win32Wrapper.FindWindowEx(IntPtr.Zero, IntPtr.Zero, null, progressBarText);
3
4 // 1. Hide the modal progress bar.
5 Win32Wrapper.ShowWindow(progressBar, Win32Wrapper.WindowShowStyle.Hide);
6
7 // 2. Send focus to AutoCAD main window.
8 IntPtr mainWindows = Autodesk.AutoCAD.ApplicationServices.Application.MainWindow.Handle;
9
10 Win32Wrapper.EnableWindow(mainWindows, true);
11 Win32Wrapper.SetFocus(mainWindows);
12 Win32Wrapper.ShowWindow(mainWindows, Win32Wrapper.WindowShowStyle.Show);
13
14 // 3. Wait for user's interaction.
15 while (...)
16 {
17 // Do interaction
18 }
19
20 // 4. Show the modal progress bar again.
21 Win32Wrapper.ShowWindow(progressBar, Win32Wrapper.WindowShowStyle.Show);
22 Win32Wrapper.SetFocus(progressBar);
2 IntPtr progressBar =Win32Wrapper.FindWindowEx(IntPtr.Zero, IntPtr.Zero, null, progressBarText);
3
4 // 1. Hide the modal progress bar.
5 Win32Wrapper.ShowWindow(progressBar, Win32Wrapper.WindowShowStyle.Hide);
6
7 // 2. Send focus to AutoCAD main window.
8 IntPtr mainWindows = Autodesk.AutoCAD.ApplicationServices.Application.MainWindow.Handle;
9
10 Win32Wrapper.EnableWindow(mainWindows, true);
11 Win32Wrapper.SetFocus(mainWindows);
12 Win32Wrapper.ShowWindow(mainWindows, Win32Wrapper.WindowShowStyle.Show);
13
14 // 3. Wait for user's interaction.
15 while (...)
16 {
17 // Do interaction
18 }
19
20 // 4. Show the modal progress bar again.
21 Win32Wrapper.ShowWindow(progressBar, Win32Wrapper.WindowShowStyle.Show);
22 Win32Wrapper.SetFocus(progressBar);
在ObjectARX中其实已经考虑到这种情况的应用了，并且提供了相应的API，这个就简单多了。
1 // Re-enable the AutoCAD main window by using StartUserInteraction
2 Autodesk.AutoCAD.ApplicationServices.Document doc =
3 Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument;
4 Editor ed = doc.Editor;
5 interaction = ed.StartUserInteraction(System.Windows.Forms.Control);
6 //...主窗口中交互操作
7 interaction.Dispose();
2 Autodesk.AutoCAD.ApplicationServices.Document doc =
3 Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument;
4 Editor ed = doc.Editor;
5 interaction = ed.StartUserInteraction(System.Windows.Forms.Control);
6 //...主窗口中交互操作
7 interaction.Dispose();
模态窗口中的操作可能会和当前的Document 相关，你当然不希望用户在中间的交互过程中更改当前活动的Document，否则的话会引起Crash，那么ObjectARX 中的 Application.DocumentManager.DocumentActivationEnabled 就是控制是否允许用户更改活动窗口(Switch drawing)的。
Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.DocumentActivationEnabled = enable;