c# - 使用绑定(bind)将椭圆与线连接起来

Question

我使用以下绑定(bind)用一条线连接两个椭圆:

Line l = new Line();
l.Stroke = Brushes.Green;
l.StrokeThickness = 3;
Binding x1 = new Binding(); x1.Path = new PropertyPath(Canvas.LeftProperty);
Binding y1 = new Binding(); y1.Path = new PropertyPath(Canvas.TopProperty);
Binding x2 = new Binding(); x2.Path = new PropertyPath(Canvas.LeftProperty);
Binding y2 = new Binding(); y2.Path = new PropertyPath(Canvas.TopProperty);
x1.Source = y1.Source = e;
x2.Source = y2.Source = e1;
l.SetBinding(Line.X1Property, x1);
l.SetBinding(Line.Y1Property, y1);
l.SetBinding(Line.X2Property, x2);
l.SetBinding(Line.Y2Property, y2);
Dependencies.Children.Add(l);

这很好用，但问题是，线条绘制在椭圆的左上角。我想使用椭圆的中心。因此，我必须将 Ellipse#width/2 添加到 x 属性。但是我该怎么做呢？

Answer 1

您可以使用 IValueConverter 在 Binding 时更改/转换值。

这是我做的东西:

Canvas Dependencies = new Canvas();
Ellipse e1 = new Ellipse() { Width = 200, Height = 200, Stroke = Brushes.Red, StrokeThickness = 1 };
Ellipse e2 = new Ellipse() { Width = 200, Height = 200, Stroke = Brushes.Red, StrokeThickness = 1 };
Line l = new Line();

l.Stroke = Brushes.Green;
l.StrokeThickness = 3;

Binding x1 = new Binding(); x1.Path = new PropertyPath(Canvas.LeftProperty); x1.Converter = new MyConverter(); x1.ConverterParameter = e1;
Binding y1 = new Binding(); y1.Path = new PropertyPath(Canvas.TopProperty); y1.Converter = new MyConverter(); y1.ConverterParameter = e1;
Binding x2 = new Binding(); x2.Path = new PropertyPath(Canvas.LeftProperty); x2.Converter = new MyConverter(); x2.ConverterParameter = e2;
Binding y2 = new Binding(); y2.Path = new PropertyPath(Canvas.TopProperty); y2.Converter = new MyConverter(); y2.ConverterParameter = e2;

x1.Source = y1.Source = e1;
x2.Source = y2.Source = e2;

l.SetBinding(Line.X1Property, x1);
l.SetBinding(Line.Y1Property, y1);
l.SetBinding(Line.X2Property, x2);
l.SetBinding(Line.Y2Property, y2);

Dependencies.Children.Add(e1);
Dependencies.Children.Add(e2);
Dependencies.Children.Add(l);

SizeChangedEventHandler act = (Object s, SizeChangedEventArgs args) =>
{
    BindingOperations.GetBindingExpressionBase(l, Line.X1Property).UpdateTarget();
    BindingOperations.GetBindingExpressionBase(l, Line.Y1Property).UpdateTarget();
    BindingOperations.GetBindingExpressionBase(l, Line.X2Property).UpdateTarget();
    BindingOperations.GetBindingExpressionBase(l, Line.Y2Property).UpdateTarget();
};

e1.SizeChanged += act;
e2.SizeChanged += act;

Canvas.SetLeft(e1, 200);
Canvas.SetTop(e1, 200);

Canvas.SetLeft(e2, 500);
Canvas.SetTop(e2, 500);

Grid2.Children.Add(Dependencies);

转换器:

public class MyConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        Ellipse e = parameter as Ellipse;
        Double d = (Double)value;

        return d + (e.ActualWidth / 2);
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        Ellipse e = parameter as Ellipse;
        Double d = (Double)value;

        return d - (e.ActualWidth / 2);
    }
}

请注意，转换器仅考虑 Ellipse.Width。您将需要对其进行修改以使其正常工作。