WPF 相对源行为

WPF RelativeSource behavior

提问by WpfBee

I have some problems in understanding RelativeSourcebinding behavior. Below is the code that binds Labelcontent to StackPanelTag correctly:

我在理解RelativeSource绑定行为方面遇到了一些问题。下面是将Label内容StackPanel正确绑定到标签的代码：

<Window x:Class="Binding_RelativeSource.MainWindow" Tag="Window Tag">
    <Grid Tag="Grid Tag">
        <StackPanel Tag="StackPanel Tag" Height="100" HorizontalAlignment="Left" Margin="156,97,0,0" Name="stackPanel1" VerticalAlignment="Top" Width="200">
            <Label Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorLevel=1,AncestorType=StackPanel},FallbackValue=BindingFailed}" Height="28" Name="label1" />
        </StackPanel>
    </Grid>
</Window>

Above code does not bind GridTag, if I change AncestorType=Gridand AncestorLevel=2. I have 2 questions:

上面的代码不绑定Grid标签，如果我改变AncestorType=Grid和AncestorLevel=2。我有两个问题：

1. I think I should change AncestorLevel to 2, to bind to Grid. But it worked for AncestorLevel=1. Why?

2. I am also not able to bind label to Window tag.Please suggest.

1. 我想我应该将 AncestorLevel 更改为 2，以绑定到 Grid。但它对AncestorLevel=1. 为什么？

2. 我也无法将标签绑定到 Window 标签。请建议。

采纳答案by WpfBee

Final conclusion from my end: It was VS2010 designer problem that it does not update RelativeSource binding for Window tag. It updates binding for other controls (I checked with Grid & StackPanel) in designer but for Winodw it gets updated at run time. Microsoft has done workaround in VS2012 for it.

我最后得出的结论是：VS2010 设计器的问题是它没有更新 Window 标签的 RelativeSource 绑定。它在设计器中更新了其他控件的绑定（我使用 Grid 和 StackPanel 进行了检查），但对于 Winodw，它会在运行时更新。微软已经在 VS2012 中为它做了解决方法。

回答by sa_ddam213

The AncestorLevelis use to find the correct ancestor to bind to, this is because there could be more than one ancestor of that type.

在AncestorLevel是利用找到正确的祖先绑定到，这是因为有可能是该类型的不止一个祖先。

Here is a scenario that shows this:

这是一个场景，显示了这一点：

<Grid Tag="AncestorLevel 3">
    <Grid Tag="AncestorLevel 2">
        <Grid Tag="AncestorLevel 1">
            <StackPanel Tag="StackPanel Tag" Height="100" HorizontalAlignment="Left" Margin="156,97,0,0" Name="stackPanel1" VerticalAlignment="Top" Width="200">
                <Label Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorLevel=1,AncestorType=Grid},FallbackValue=BindingFailed}" Height="28"  />
                <Label Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorLevel=2,AncestorType=Grid},FallbackValue=BindingFailed}" Height="28"  />
                <Label Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorLevel=3,AncestorType=Grid},FallbackValue=BindingFailed}" Height="28"  />
            </StackPanel>
        </Grid>
    </Grid>
</Grid>

Result:

结果：

Alternative Method

替代方法

But you can simplify the code by using ElementNamebinding, this uses the Nameof the element

但是您可以通过使用ElementName绑定来简化代码，这使用Name了元素的

Example:

例子：

<Window x:Class="WpfApplication9.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" Name="MyWindow" Tag="This is the window">
    <Grid Name="Grid1" Tag="First grid">
        <Grid Name="Grid2" Tag="Second grid">
            <Grid Name="Grid3" Tag="ThirdGrid">
                <StackPanel Name="stackPanel1" Tag="StackPanel Tag" Height="160" HorizontalAlignment="Left" Margin="156,97,0,0" VerticalAlignment="Top" Width="200">
                    <Label Content="{Binding ElementName=MyWindow, Path=Tag}" Height="28"  />
                    <Label Content="{Binding ElementName=Grid1, Path=Tag}" Height="28"  />
                    <Label Content="{Binding ElementName=Grid2, Path=Tag}" Height="28"  />
                    <Label Content="{Binding ElementName=Grid3, Path=Tag}" Height="28"  />
                    <Label Content="{Binding ElementName=stackPanel1, Path=Tag}" Height="28"  />
                </StackPanel>
            </Grid>
        </Grid>
    </Grid>
</Window>

Result:

结果：

If you want to bind back to the Windowyou can still use FindAncestor

如果你想绑定回Window你仍然可以使用FindAncestor

<Window x:Class="WpfApplication9.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" Tag="This is the window">
    <Grid>
        <StackPanel Height="100" HorizontalAlignment="Left" Margin="156,97,0,0" Name="stackPanel1" VerticalAlignment="Top" Width="200">
            <Label Content="{Binding Path=Tag,RelativeSource={RelativeSource Mode=FindAncestor,AncestorType=Window},FallbackValue=BindingFailed}" Height="28"  />
        </StackPanel>
    </Grid>

Result:

结果：