将自定义 AttachedProperty 绑定到工具提示 - 错误？

Question

我想将自定义 AttachedProperty 的值绑定到 ToolTip 的内容。

绑定有效，但仅在工具提示的第二次打开时有效。当工具提示第一次打开时，绑定有它的 FallbackValue。

奇怪的是，它适用于“默认”附加属性，例如 Grid.Row。

谁能解释一下？

代码很简单：

<Button local:AttachedProperty.TestProperty="Now it works!" Content="Button">
    <Button.ToolTip>
        <ToolTip DataContext="{Binding Path=PlacementTarget, RelativeSource={x:Static RelativeSource.Self}}">
            <TextBlock Text="{Binding (local:AttachedProperty.TestProperty), FallbackValue=&quot;It doesn't work&quot;}" />
        </ToolTip>
    </Button.ToolTip>
</Button>

AttachedProperty的代码：

public static class AttachedProperty
{
    public static readonly DependencyProperty TestPropertyProperty = DependencyProperty.RegisterAttached
    (
        "TestProperty",
        typeof(string),
        typeof(AttachedProperty),
        new FrameworkPropertyMetadata
        (
            string.Empty,
            FrameworkPropertyMetadataOptions.Inherits
        )
    );

    public static string GetTestProperty(FrameworkElement target)
    {
        return (string)target.GetValue(TestPropertyProperty);
    }

    public static void SetTestProperty(FrameworkElement target, string value)
    {
        target.SetValue(TestPropertyProperty, value);
    }
}

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

编辑 1：解决方案和新问题：

当我在工具提示中再次定义命名空间“本地”时，我发现它有效：

<ToolTip xmlns:local="clr-namespace:Test" DataContext=...

但是

如果您想在样式中执行此操作，则会出现错误

"XMLNamespace", "Assembly" or "ClrNamespace" not found in Mapping Expression

我的新测试项目的 XML 代码是：

<Grid x:Name="LayoutRoot">
    <Grid.Resources>
        <Style TargetType="{x:Type Button}">
            <Setter Property="ToolTip">
                <Setter.Value>
                    <ToolTip xmlns:local="clr-namespace:Test" DataContext="{Binding Path=PlacementTarget, RelativeSource={x:Static RelativeSource.Self}}" >
                <TextBlock  Text="{Binding (local:AttachedProperty.TestProperty), FallbackValue=&quot;It doesn't work&quot;}" />
            </ToolTip>
                </Setter.Value>
            </Setter>
        </Style>
    </Grid.Resources>

    <Button local:AttachedProperty.TestProperty="Now it works!" Content="Button" HorizontalAlignment="Center" VerticalAlignment="Center" />
</Grid>

Answer 1

我在 PropertyChangedCallback 中添加了一些跟踪输出（并删除了 Inherits 标志，因为它在这里没用）：

public static readonly DependencyProperty TestPropertyProperty =
    DependencyProperty.RegisterAttached(
        "TestProperty",
        typeof(string),
        typeof(AttachedProperty),
        new FrameworkPropertyMetadata(
            string.Empty,
            (o, e) => Trace.TraceInformation("Setting TestProperty = \"{1}\" on {0}", o, e.NewValue))
);

Visual Studio 输出证明该属性在绑定抱怨找不到之前已设置：

ToolTipAttachedProperty.vshost.exe Information: 0 : Setting TestProperty = "Now it works!" on System.Windows.Controls.Button
System.Windows.Data Warning: 40 : BindingExpression path error: '(local:AttachedProperty.TestProperty)' property not found on 'object' ''Button' (Name='')'. BindingExpression:Path=(local:AttachedProperty.TestProperty); DataItem='Button' (Name=''); target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String')

您或许应该将此发送给 Microsoft。

编辑：参考您关于将工具提示放入样式的编辑。你可以这样写：

<Grid.Resources>
    <ToolTip xmlns:local="clr-namespace:Test" x:Key="ButtonToolTip"
             DataContext="{Binding Path=PlacementTarget, RelativeSource={x:Static RelativeSource.Self}}">
        <TextBlock Text="{Binding (local:AttachedProperty.TestProperty), FallbackValue=&quot;It doesn't work&quot;}" />
    </ToolTip>
    <Style TargetType="Button">
        <Setter Property="ToolTip" Value="{StaticResource ButtonToolTip}"/>
    </Style>
</Grid.Resources>