Picking Two Points Consecutively

Here is a question on picking points while interacting with a modeless dialogue:

Question: I want to pick two points consecutively using PickPoint.

I am using a modeless dialog, and have a section of code that is called when a button is pressed.

However, after picking the first point, an exception is thrown saying "The user aborted the pick operation".

Do you have a solution?

Answer: I implemented a sample application providing an external command PickTwoPoints for you to demonstrate one possible solution.

I use the following code to generate and display a modeless dialogue to the user before the picking is initiated:

  Form DisplayModelessForm( IWin32Window owner )
  {
    System.Windows.Forms.Form form
      = new System.Windows.Forms.Form();
    form.Size = new Size( 300, 100 );
    form.Text = "Pick Two Points Modeless Form";
    form.Show( owner );
    return form;
  }

The form is initially displayed, then hidden again before calling PickPoint.

As always when displaying a modeless form, I define its owner window to be the Revit main frame.

I use my JtWindowHandle wrapper class to convert the IntPtr returned by the Autodesk.Windows.ComponentManager ApplicationWindow property to an IWin32Window, which can be passed in to the form Show method to set its owner:

  /// <summary>
  /// Wrapper class for converting 
  /// IntPtr to IWin32Window.
  /// </summary>
  public class JtWindowHandle : IWin32Window
  {
    IntPtr _hwnd;
 
    public JtWindowHandle( IntPtr h )
    {
      Debug.Assert( IntPtr.Zero != h,
        "expected non-null window handle" );
 
      _hwnd = h;
    }
 
    public IntPtr Handle
    {
      get
      {
        return _hwnd;
      }
    }
  }

The external command Execute method performs the following steps:

• Determine the main Revit application window handle.
• Display the dynamically generated modeless form.
• Hide the form.
• Select the two points.
• Process the two resulting points, in this case by displaying them in the Visual Studio debug output window.
• Redisplay the modeless form.
• Close and terminate.

Here is the whole resulting Execute method mainline code implementing this:

public Result Execute(
  ExternalCommandData commandData,
  ref string message,
  ElementSet elements )
{
  IWin32Window revit_window
    = new JtWindowHandle(
      ComponentManager.ApplicationWindow );
 
  UIApplication uiapp = commandData.Application;
  UIDocument uidoc = uiapp.ActiveUIDocument;
  Selection sel = uidoc.Selection;
 
  using( Form form = DisplayModelessForm( 
    revit_window ) )
  {
    form.Hide();
 
    try
    {
      XYZ p = sel.PickPoint( "Point 1" );
 
      XYZ q = sel.PickPoint( "Point 2" );
 
      Debug.Print( string.Format(
        "The two points you selected are {0} and {1}.",
        PointString( p ), PointString( q ) ) );
    }
    catch( Exception e )
    {
      Debug.Print( e.Message );
    }
 
    form.Show();
  }
  return Result.Succeeded;
}

As it now stands, this can obviously be packaged in an external command using read-only transaction mode, since the database is not affected in any way.

Here is PickTwoPoints.zip containing the complete source code, entire Visual Studio solution and add-in manifest of the PickTwoPoints external command.

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This is part of his Windows Azure experiential learning series.

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