RegisterName throws NullReferenceException

Question

Hi I am having a problem registering a controls name, so that I can remove the control when I need to redraw it. when trying to register the name it throws a NullReferenceException, can anyone see a problem with the code?

private void DrawSegment(Point p1, Point p2, Point p3, Point p4, bool reflexangle, Color clr)
    {

      // Segment Geometry
      PathSegmentCollection segments = new PathSegmentCollection();

      // First line segment from pt p1 - pt p2
      segments.Add(new LineSegment() { Point = p2 });

      //Arc drawn from pt p2 - pt p3 with the RangeIndicatorRadius 
      segments.Add(new ArcSegment()
      {
        Size = new Size(arcradius2, arcradius2),
        Point = p3,
        SweepDirection = SweepDirection.Clockwise,
        IsLargeArc = reflexangle

      });

      // Second line segment from pt p3 - pt p4
      segments.Add(new LineSegment() { Point = p4 });

      //Arc drawn from pt p4 - pt p1 with the Radius of arcradius1 
      segments.Add(new ArcSegment()
      {
        Size = new Size(arcradius1, arcradius1),
        Point = p1,
        SweepDirection = SweepDirection.Counterclockwise,
        IsLargeArc = reflexangle

      });

      // Defining the segment path properties
      Color rangestrokecolor;
      if (clr == Colors.Transparent)
      {
        rangestrokecolor = clr;
      }
      else
        rangestrokecolor = Colors.White;


      rangeIndicator = new Path()
      {
        StrokeLineJoin = PenLineJoin.Round,
        Stroke = new SolidColorBrush(rangestrokecolor),
        Fill = new SolidColorBrush(clr),
        Opacity = 0.65,
        StrokeThickness = 0.25,
        Data = new PathGeometry()
        {
          Figures = new PathFigureCollection()
           {
            new PathFigure()
            {
              IsClosed = true,
              StartPoint = p1,
              Segments = segments
            }
          }
        }
      };

      //Set Z index of range indicator
      rangeIndicator.SetValue(Canvas.ZIndexProperty, 150);


      //give the UI element a name so that we can redraw it
      rangeIndicator.Name = "RangeIndicatorSeg";
      rootGrid.RegisterName(rangeIndicator.Name, rangeIndicator); //this fails with a NullReferencException
      // Adding the segment to the root grid 
      rootGrid.Children.Add(rangeIndicator);

    }

    void RedrawRange()
    {
      rootGrid.Children.Remove((UIElement)this.FindName("RangeIndicatorSeg"));
      DrawRangeIndicator();
      
    }

Many Thanks,

 

Robin.

---

Welcome to my world

Answer 1

Hi Playwolf,

In that line, the only possible reason that will raise the NullRederenceException is that the rootGrid or rangeIndicator is null, so you can check those two variables if they are null.

Hope this helps.

Best regards,
Kevin Pan

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Answer 2

After further investigation I found that I needed to set the namespace programmatically...

This fixed the program.

 

Many Thanks,

Robin.

---

Welcome to my world