wpf 如何将绑定中的 FallbackValue 设置为外部图像文件的路径？
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How to set FallbackValue in binding as path to external image file?
提问by h__
I'm trying to set FallbackValue in case when my converter cannot be call, but I'm not sure how to do that.
我正在尝试设置 FallbackValue，以防我的转换器无法调用，但我不知道该怎么做。
<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" />
Paths of external images in converter looks like that and when LatestPosition!=null the image is set in proper way.
转换器中外部图像的路径看起来像这样，当 LatexPosition!=null 时，图像以正确的方式设置。
private static readonly ImageSource Dev1 = new BitmapImage(new Uri("/Pictures/dev1.png", UriKind.Relative));
private static readonly ImageSource Dev2 = new BitmapImage(new Uri("/Pictures/dev2.png", UriKind.Relative));
回答by coldjokelife
For the Image control, when you Binding the Source property with a URI string, it will automatically convert the URI to a BitmapImage. But if you set the FallbackValue and TargetNullValue as URI string, it will not display.
对于 Image 控件，当您将 Source 属性与 URI 字符串绑定时，它会自动将 URI 转换为 BitmapImage。但是如果将 FallbackValue 和 TargetNullValue 设置为 URI 字符串，则不会显示。
You need to set it as BitmapImage:
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}}" />
As we set the FallbackValue and the TargetNullValue as StaticResource of BitmapImage, It works.
当我们将 FallbackValue 和 TargetNullValue 设置为 BitmapImage 的 StaticResource 时，它起作用了。
回答by Anatoliy Nikolaev
For myself, I created the following example:
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>
The path to the images, I announced in resources. Images are stored in the root of the project. Listing of MyTestData:
图片的路径，我在资源中公布了。图像存储在项目的根目录中。清单MyTestData：
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;
}
}
