Source = null的ImageSourceConverter错误 [英] ImageSourceConverter error for Source=null

问题描述

我将一个图像的Source属性绑定到一个字符串。此字符串可能为null，在这种情况下，我不想显示图像。但是，我在调试输出中得到以下内容：

System.Windows.Data错误：23：不能
转换'< null>'从类型'< null>'到
类型
'System.Windows.Media.ImageSource'为
'en-AU'文化与默认
转换;考虑使用Binding的Converter
属性。
NotSupportedException：'System.NotSupportedException：
ImageSourceConverter无法从（null）转换
。在
System.ComponentModel.TypeConverter.GetConvertFromException（Object
value）at
System.Windows.Media.ImageSourceConverter.ConvertFrom（ITypeDescriptorContext
context，CultureInfo culture，Object
值）
MS.Internal.Data.DefaultValueConverter.ConvertHelper（Object
o，Type destinationType，
DependencyObject targetElement，
CultureInfo culture，Boolean
isForward）'

我宁愿不显示，因为它只是噪音 - 有什么办法压制吗？

解决方案

@AresAvatar正确建议您使用ValueConverter，但该实现并不能帮助您。这样做：

  public class NullImageConverter：IValueConverter 
 {
 public object Convert（object value，Type targetType ，object参数，CultureInfo文化）
 {
 if（value == null）
返回DependencyProperty.UnsetValue; 
返回值; 
} 
 
 public object ConvertBack（object value，Type targetType，object parameter，CultureInfo culture）
 {
 //根据https://msdn.microsoft。 com / en-us / library / system.windows.data.ivalueconverter.convertback（v = vs.110）.aspx＃Anchor_1 
 //（kudos Scott Chamberlain），如果你不支持转换
 //返回你应该返回一个Binding.DoNothing或
 // DependencyProperty.UnsetValue 
 return Binding.DoNothing; 
 //原始代码：
 // throw new NotImplementedException（）; 
} 
} 
  

返回 DependencyProperty.UnsetValue 还解决了抛出（并忽略）所有这些异常的性能问题。返回一个新的BitmapSource（uri）也可以摆脱异常，但仍然有一个性能命中（没有必要）。

当然，您还需要管道：

在资源中：

 < local：NullImageConverter x：Key =nullImageConverter/> 
  

您的图片：

 < Image Source ={Binding Path = ImagePath，Converter = {StaticResource nullImageConverter}}/> 
  

I'm binding the Source property of an Image to a string. This string may be null in which case I just don't want to display an Image. However, I'm getting the following in my Debug output:

System.Windows.Data Error: 23 : Cannot convert '<null>' from type '<null>' to type 'System.Windows.Media.ImageSource' for 'en-AU' culture with default conversions; consider using Converter property of Binding. NotSupportedException:'System.NotSupportedException: ImageSourceConverter cannot convert from (null). at System.ComponentModel.TypeConverter.GetConvertFromException(Object value) at System.Windows.Media.ImageSourceConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value) at MS.Internal.Data.DefaultValueConverter.ConvertHelper(Object o, Type destinationType, DependencyObject targetElement, CultureInfo culture, Boolean isForward)'

I'd prefer if this wasn't displayed as it's just noise - is there any way to suppress it?

解决方案

@AresAvatar is right in suggesting you use a ValueConverter, but that implementation does not help the situation. This does:

public class NullImageConverter :IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == null)
            return DependencyProperty.UnsetValue;
        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        // According to https://msdn.microsoft.com/en-us/library/system.windows.data.ivalueconverter.convertback(v=vs.110).aspx#Anchor_1
        // (kudos Scott Chamberlain), if you do not support a conversion 
        // back you should return a Binding.DoNothing or a 
        // DependencyProperty.UnsetValue
        return Binding.DoNothing;
        // Original code:
        // throw new NotImplementedException();
    }
}

Returning DependencyProperty.UnsetValue also addresses the performance issues from throwing (and ignoring) all those exceptions. Returning a new BitmapSource(uri) would also get rid of the exceptions, but there is still a performance hit (and it isn't necessary).

Of course, you'll also need the plumbing:

In resources:

<local:NullImageConverter x:Key="nullImageConverter"/>

Your image:

<Image Source="{Binding Path=ImagePath, Converter={StaticResource nullImageConverter}}"/>

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