C# 如何将绑定中的FallbackValue设置为外部映像文件的路径？

我试图设置FallbackValue，以防我的转换器无法调用，但我不知道如何做到这一点

<Image Source="{Binding FallbackValue="Pictures/Unknown.png", Path=LatestPosition.DeviceFamily, Converter={x:Static conv:ConverterSet.DeviceTypeToImageSourceconverter}}" Name="image1" Stretch="Fill" Margin="5,8" Width="150" Height="150" Grid.RowSpan="4" />

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对于我自己，我创建了以下示例：

<!-- xmlns:sys="clr-namespace:System;assembly=mscorlib" -->

<Window.Resources>
    <!-- Test data -->
    <local:TestDataForImage x:Key="MyTestData" />

    <!-- Image for FallbackValue -->
    <sys:String x:Key="ErrorImage">pack://application:,,,/NotFound.png</sys:String>

    <!-- Image for NULL value -->
    <sys:String x:Key="NullImage">pack://application:,,,/NullImage.png</sys:String>
</Window.Resources>

<!-- Grid using DataContext -->
<Grid DataContext="{StaticResource MyTestData}">
    <Image Name="ImageNull" Width="100" Height="100" HorizontalAlignment="Left" VerticalAlignment="Bottom" Source="{Binding Path=NullString, TargetNullValue={StaticResource NullImage}}" />

    <Image Name="ImageNotFound" Width="100" Height="100" HorizontalAlignment="Left" VerticalAlignment="Top" Source="{Binding Path=NotFoundString, FallbackValue={StaticResource ErrorImage}}" />
</Grid>

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对于图像控件，当您使用URI字符串绑定源属性时，它将自动将URI转换为BitmapImage。 但是如果将FallbackValue和TargetNullValue设置为URI字符串， 它不会显示

您需要将其设置为BitmapImage：

<Window.Resources>
    <BitmapImage x:Key="DefaultImage" UriSource="/Resources;component/Images/Default.jpg" />
</Window.Resources>

<Image Width="128"
               Height="128"
               HorizontalAlignment="Left"
               VerticalAlignment="Top"
               Source="{Binding Photo,FallbackValue={StaticResource DefaultImage},
                                TargetNullValue={StaticResource DefaultImage}}" />

当我们将FallbackValue和TargetNullValue设置为BitmapImage的StaticResource时，

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它可以工作。

代替“Pictures/Unknown.png”指定完整路径是的，它只在文件存在时解决问题。如果我保留未知文件并将其包含在可执行文件中，并且我可以使用Uri（“/Pic/nam.png”）访问该文件，而不能使用FallbackValue的同一文件的相对路径访问该文件，那么有什么区别？

public class TestDataForImage : DependencyObject
{
    public string NotFoundString
    {
        get
        {
            return (string)GetValue(NotFoundStringProperty);
        }

        set
        {
            SetValue(NotFoundStringProperty, value);
        }
    }

    public static readonly DependencyProperty NotFoundStringProperty = DependencyProperty.Register("NotFoundString", typeof(string), typeof(TestDataForImage), new PropertyMetadata(""));

    public string NullString
    {
        get
        {
            return (string)GetValue(NullStringProperty);
        }

        set
        {
            SetValue(NullStringProperty, value);
        }
    }

    public static readonly DependencyProperty NullStringProperty = DependencyProperty.Register("NullString", typeof(string), typeof(TestDataForImage), new PropertyMetadata(""));

    public TestDataForImage()
    {
        NotFoundString = "pack://application:,,,/NotExistingImage.png";
        NullString = null;
    }
}

<Window.Resources>
    <BitmapImage x:Key="DefaultImage" UriSource="/Resources;component/Images/Default.jpg" />
</Window.Resources>

<Image Width="128"
               Height="128"
               HorizontalAlignment="Left"
               VerticalAlignment="Top"
               Source="{Binding Photo,FallbackValue={StaticResource DefaultImage},
                                TargetNullValue={StaticResource DefaultImage}}" />