SetTarget vs RegisterName / SetTargetName

Question

Here's a simple program which animates the Y2 property of a Line shape. Note that I use the SetTarget method to target the Line . This program works fine.

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SoGeneratingAnimatedLine
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            var canvas = new Canvas();

            Content = canvas;

            var sb = new Storyboard();

            var line = new Line()
            {
                X1 = 10, Y1 = 10,
                X2 = 90, Y2 = 10,
                Stroke = Brushes.Black,
                StrokeThickness = 2
            };

            canvas.Children.Add(line);

            var animation = new DoubleAnimation(10, 90, new Duration(TimeSpan.FromMilliseconds(1000)));

            sb.Children.Add(animation);

            Storyboard.SetTarget(animation, line);
            Storyboard.SetTargetProperty(animation, new PropertyPath(Line.Y2Property));

            MouseDown += (s, e) => sb.Begin(this);
        }
    }
}

Here's a similar program which animates the EndPoint of a LineGeometry which is the Data for a Path :

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SoGeneratingAnimatedLine
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            var canvas = new Canvas();

            Content = canvas;

            var sb = new Storyboard();

            var lineGeometry = 
                new LineGeometry(new Point(10, 10), new Point(90, 10));

            var path = new Path()
            {
                Stroke = Brushes.Black,
                StrokeThickness = 2,
                Data = lineGeometry
            };

            canvas.Children.Add(path);

            var animation =
                new PointAnimation(
                    new Point(90, 10),
                    new Point(90, 90),
                    new Duration(TimeSpan.FromMilliseconds(1000)));

            sb.Children.Add(animation);

            Storyboard.SetTarget(animation, lineGeometry);
            Storyboard.SetTargetProperty(animation, new PropertyPath(LineGeometry.EndPointProperty));

            MouseDown += (s, e) => sb.Begin(this);
        }
    }
}

This second version does not work. However, if I replace the line:

Storyboard.SetTarget(animation, lineGeometry);

with:

RegisterName("geometry", lineGeometry);
Storyboard.SetTargetName(animation, "geometry");

then the animation runs.

Why doesn't the SetTarget version of the second program work? When is it OK to use SetTarget instead of the RegisterName / SetTargetName combo? What's the difference in the two approaches?

Answer 1

There is no need at all for a Storyboard. Just call BeginAnimation directly on the LineGeometry:

lineGeometry.BeginAnimation(LineGeometry.EndPointProperty, animation);

Answer 2

Calling RegisterName is necessary in order to correctly hook up animation storyboards for applications when created in code. This is because one of the key storyboard properties, TargetName , uses a run-time name lookup instead of being able to take a reference to a target element. This is true even if that element is accessible by reference from the code.