c# - WPF Multibinding RelativeSource Findancestor 评估性能

Question

对于以下 MultiBinding 表达式，如果多次更改 PropB，绑定(bind)引擎将搜索 DataGrid 祖先多少次？

<MultiBinding Converter="{StaticResource TestConverter}"> 
    <Binding Path="PropA"/> 
    <Binding Path="PropB" /> 
    <Binding Path="DataContext.Sub.PropertyC" RelativeSource="{RelativeSource Mode=FindAncestor,AncestorType=DataGrid}" /> 
</MultiBinding>

如果 PropertyC(及其路径)从未改变，它是否只搜索一次？还是每次更改多重绑定(bind)中的一个属性时它都会搜索祖先？假设每个属性都有更改通知。

Answer 1

我认为唯一可行的测试方法是实际删除控件，以查看它是否找到了正确的控件。

以这种方式进行测试，无论是否使用 MultiBinding，它看起来都只被评估一次。

<Window x:Class="RelativeTest.MainWindow"
        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"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel x:Name="Stack">
        <TextBlock x:Name="TB1" Text="Foo" />
        <TextBlock x:Name="TB2" Text="Bar" />

        <Border BorderThickness="1" BorderBrush="Black" />

        <TextBlock Text="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=StackPanel}, Path=Children[0].Text}" 
                   Foreground="Red" />

        <TextBlock Foreground="Blue">
            <TextBlock.Text>
                <MultiBinding StringFormat="{}{2}">
                    <Binding ElementName="TB1" Path="Text" />
                    <Binding ElementName="TB2" Path="Text" />
                    <Binding RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType=StackPanel}" Path="Children[0].Text" />
                </MultiBinding>
            </TextBlock.Text>
        </TextBlock>
        <Button Click="ButtonBase_OnClick" Content="Remove 1st Child" />
    </StackPanel>
</Window>

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    void ButtonBase_OnClick(object sender, RoutedEventArgs e)
    {
        Stack.Children.Remove(Stack.Children[0]);
        TB1.Text = "You'll see me if I am looked up once.";
        TB2.Text = "You'll see me twice if I am re-evaulated each time";
    }
}

最初运行它时你会看到:

单击按钮时，它将删除第一个子项并更改 TextBlocks 以显示更新的文本以指示它现在绑定(bind)到哪个子项。