如何将多边形绑定到 WPF 中的现有 PointCollection？

How do I bind a Polygon to an existing PointCollection in WPF?

提问by EdwinG

My current implementation doesn't show anything on the form even though the collections I thought bounded have data (I checked in debug).

即使我认为有界的集合有数据（我在调试中检查），我当前的实现也没有在表单上显示任何内容。

Here's some code:

这是一些代码：

    public event PropertyChangedEventHandler PropertyChanged;
    PointCollection imagePoints;
    public PointCollection ImagePoints
    {
        get
        {
            return this.imagePoints;
        }
        set
        {
            if (this.imagePoints != value)
            {
                this.imagePoints = value;
                if (this.PropertyChanged != null)
                {
                    PropertyChanged(this, new PropertyChangedEventArgs("ImagePoints"));
                }
            }
        }
    }

and the corresponding xaml:

和相应的xaml：

<Polygon x:Name="imagePolygon" Points="{Binding ImagePoints}" Stretch="Fill" Fill="Black" Opacity="0.8" />

Now, I did all the binding by writing the code. In this example, it works just fine, yet in mine, the points don't show up on the polygon.

现在，我通过编写代码完成了所有绑定。在这个例子中，它工作得很好，但在我的例子中，点没有出现在多边形上。

Any pearls of wisdom?

有智慧的珍珠吗？

Edit:here's the complete xaml code

编辑：这是完整的 xaml 代码

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" mc:Ignorable="d" x:Class="WpfApplication2.HistogramWindow"
    Title="HistogramWindow" Height="436" Width="604">
<Grid>
    <TabControl HorizontalAlignment="Left" Height="406" VerticalAlignment="Top" Width="596" >
        <TabItem x:Name="imageTab" Header="Full Image" Height="23" VerticalAlignment="Top">
            <Border BorderBrush="Black" BorderThickness="1" Margin="10">
                <Polygon x:Name="imagePolygon" Points="{Binding ImagePoints}" Stretch="Fill" Fill="Black" Opacity="0.8" />
            </Border>
        </TabItem>
        <TabItem x:Name="boneTab" Header="Bone">
            <Border BorderBrush="Black" BorderThickness="1" Margin="10">
                <Border.BindingGroup>
                    <BindingGroup/>
                </Border.BindingGroup>
                <Polygon x:Name="bonePolygon" Points="{Binding BonePoints}" Stretch="Fill" Fill="Black" Opacity="0.8" >

                </Polygon>
            </Border>
        </TabItem>
        <TabItem x:Name="fatTab" Header="Fat" HorizontalAlignment="Left" Height="20" VerticalAlignment="Top" Width="57">
            <Border BorderBrush="Black" BorderThickness="1" Margin="10">
                <Polygon x:Name="fatPolygon" Points="{Binding FatPoints}" Stretch="Fill" Fill="Black" Opacity="0.8" />
            </Border>
        </TabItem>
    </TabControl>

</Grid>

Edit: After a modification of the config file, I find this in the output window:

编辑：修改配置文件后，我在输出窗口中找到了这个：

System.Windows.Data Information: 41 : BindingExpression path error: 'ImagePoints'   property not found for 'object' because data item is null.  This could happen because the data provider has not produced any data yet. BindingExpression:Path=ImagePoints; DataItem=null; target element is 'Polygon' (Name='imagePolygon'); target property is 'Points' (type 'PointCollection')
System.Windows.Data Information: 20 : BindingExpression cannot retrieve value due to missing information. BindingExpression:Path=ImagePoints; DataItem=null; target element is 'Polygon' (Name='imagePolygon'); target property is 'Points' (type 'PointCollection')
System.Windows.Data Information: 21 : BindingExpression cannot retrieve value from null data item. This could happen when binding is detached or when binding to a Nullable type that has no value. BindingExpression:Path=ImagePoints; DataItem=null; target element is 'Polygon' (Name='imagePolygon'); target property is 'Points' (type 'PointCollection')
System.Windows.Data Information: 10 : Cannot retrieve value using the binding and no valid fallback value exists; using default instead. BindingExpression:Path=ImagePoints; DataItem=null; target element is 'Polygon' (Name='imagePolygon'); target property is 'Points' (type 'PointCollection')

回答by Peter Hansen

I'm not sure why you are getting binding errors, but on first sight the code you have looks fine.

我不确定为什么会出现绑定错误，但乍一看，您拥有的代码看起来不错。

I have written a small piece of code that works, so you can check that out and see if you have missed something. I guess it must be kinda similar to yours..

我写了一小段有效的代码，所以你可以检查一下，看看你是否遗漏了什么。我想它应该和你的有点相似..

Relevant part of the XAML:

XAML 的相关部分：

<TabItem x:Name="imageTab" Header="Full Image" Height="23" VerticalAlignment="Top">
    <Border BorderBrush="Black" BorderThickness="1" Margin="10">
        <StackPanel>
            <Polygon x:Name="imagePolygon" Points="{Binding ImagePoints}" Stretch="Fill" Fill="Black" Opacity="0.8" />
            <Button Content="Set new points" Click="btnSetNew" />
        </StackPanel>
    </Border>
</TabItem>

Code-behind for the window:

窗口的代码隐藏：

public partial class Window1 : Window, INotifyPropertyChanged
{
    public Window1()
    {
        InitializeComponent();

        this.ImagePoints = new PointCollection
            (new [] { new Point(1, 2), new Point(34, 12), new Point(12, 99) });

        //Important - maybe you missed this?
        this.DataContext = this;
    }

    public event PropertyChangedEventHandler PropertyChanged;
    PointCollection imagePoints;
    public PointCollection ImagePoints
    {
        get
        {
            return this.imagePoints;
        }
        set
        {
            if (this.imagePoints != value)
            {
                this.imagePoints = value;
                if (this.PropertyChanged != null)
                {
                    PropertyChanged(this, new PropertyChangedEventArgs("ImagePoints"));
                }
            }
        }
    }

    private void btnSetNew(object sender, RoutedEventArgs e)
    {
        this.ImagePoints = new PointCollection(
            new[] { new Point(23, 2), new Point(12, 556), new Point(4, 89) });
    }
}