如何将派生<UserControl>的元素绑定到基的元素<UserControl>？
我已经定义了一个名为 Tile 的 UserControl 作为我的基类。这将是一个抽象基类，如果当我尝试实例化从它派生的对象时 XAML 不会犹豫...
无论如何，到目前为止 Tile 只包含一个依赖属性：OuterShape。它是一个 System.Windows.Shapes.Shape 对象（也是抽象的）。因此：所有图块都将具有某种与其相关联的视觉形状，用于渲染。但是有许多不同类型的 Tiles —— 有些带有 System.Windows.Shapes.Paths，有些带有 System.Windows.Shapes.Polygons，等等。
所以现在我正在研究第一个派生的 UserControl：PolyTile。顾名思义，这是一个使用 System.Windows.Shapes.Polygon 作为其“OuterShape”属性的 Tile。
我遇到的问题是我无法弄清楚如何将 XAML<Polygon>元素成功绑定到基类中的 Shape 属性。
/************
** Tile.cs **
************/
// This class contains a generic shape, and that's all.
// This class does NOT have a XAML file to go with it. It is purely code implemented.
public class Tile : System.Windows.Controls.UserControl
{
public static readonly System.Windows.DependencyProperty OuterShapeProperty
= System.Windows.DependencyProperty.Register( "OuterShape",
typeof(System.Windows.Shapes.Shape),
typeof(Tile));
public System.Windows.Shapes.Shape OuterShape
{ get { return (System.Windows.Shapes.Shape)GetValue(OuterShapeProperty); }
set { SetValue(OuterShapeProperty, (System.Windows.Shapes.Shape)value); }
}
}
………………………………………………………………………………
<!--*****************
*** PolyTile.xaml ***
******************-->
<local:Tile x:Name="__PolyTile__" x:Class="WPFApplication1.PolyTile"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:WPFApplication1">
<Grid Name="grdMain">
<Polygon Name="OuterPoly" />
<!--OuterPoly needs to be data-bound (OneWay)
to the OuterShape property of the Tile UserControl.
That way, when my derived class sets OuterShape to a new <Polygon> element,
OuterShape will show up on the screen as a <Polygon>-->
</Grid>
</local:Tile>
………………………………………………………………………………
/****************
** PolyTile.cs **
****************/
// This class encapsulates a tile that is in the shape of a specified <Polygon> element.
/// <summary>
/// Interaction logic for PolyTile.xaml
/// </summary>
public partial class PolyTile : Tile // Derived from Tile
{
public PolyTile()
{
InitializeComponent();
System.Windows.Data.BindingExpressionBase BindExp;
PolyConverter polyConverter = new PolyConverter();
System.Windows.Data.Binding PolyBinding = new System.Windows.Data.Binding("OuterPoly");
PolyBinding.Source = __PolyTile__;
PolyBinding.Mode = System.Windows.Data.BindingMode.OneWayToSource;
PolyBinding.Converter = polyConverter;
BindExp = __PolyTile__.SetBinding(Tile.OuterShapeProperty, PolyBinding);
}
// The framework won't convert a base object into a derived object without an explicit cast ...
// ... in this case, that means I have to make a custom DataConverter.
[System.Windows.Data.ValueConversion(typeof(System.Windows.Shapes.Polygon), typeof(System.Windows.Shapes.Shape))]
protected class PolyConverter : System.Windows.Data.IValueConverter
{
public object Convert(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{ return value; }
// OneWayToSource binding: Thus the Convert method is never used.
// Rather, ConverBack is used to cast the base <Shape> into a derived <Polygon>
public object ConvertBack(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value.GetType() == typeof(System.Windows.Shapes.Polygon))
return value;
else
return System.Windows.DependencyProperty.UnsetValue;
}
}
}
我看不到在 XAML 中设置此绑定的任何可能方法。（虽然我对 DataContexts 的理解不够好，不能说我已经想到了一切......）
因此，我尝试在后台代码中手动设置绑定。我尝试了许多不同的方法来组织绑定路径以及源和目标元素。每次我遇到致命异常或 PathError 或 UpdateSourceError 类似的东西。
有谁知道我做错了什么？
任何意见是极大的赞赏！