解决方案绑定设置Image.Source为绑定为空引发的错误。 （SUP pression？） [英] Solution to binding errors thrown by setting Image.Source to a binding to null. (suppression?)
问题描述
我有一种情况，我必须设置为null图像源将在稍后解决，然后显示出来。以$ P $什么好的办法从抛出绑定错误pvent我的code？
一个例子：
System.Windows.Data错误：23：不能'从类型''转换为键入'System.Windows.Media.ImageSource'为'EN-US使用默认的转换文化;考虑使用绑定的转换器属性。 NotSupportedException异常：的System.NotSupportedException：ImageSourceConverter无法从（空）转换。
在System.ComponentModel.TypeConverter.GetConvertFromException（对象的值）
在System.Windows.Media.ImageSourceConverter.ConvertFrom（ITypeDescriptorContext方面，CultureInfo的文化，对象的值）
在MS.Internal.Data.DefaultValueConverter.ConvertHelper（对象o，类型destinationType，DependencyObject的targetElement，CultureInfo的文化，布尔isForward）编辑：按要求
＆lt;图像X：NAME =形象HEIGHT =自动WIDTH =自动不透明度=0＆GT;
＆LT; Image.Effect＆GT;
＆LT; DropShadowEffect /＆GT;
＆LT; /Image.Effect>
＆LT; Image.Source＆GT;
＆LT;绑定路径=的ImageStream＆GT;
＆LT; Binding.ValidationRules＆GT;
＆LT; validationRules：NotNullStreamValidationRule /＆GT;
＆LT; /Binding.ValidationRules>
＆LT; /装订＆GT;
＆LT; /Image.Source>
＆LT; /图像＆GT;
命名空间FlickrDemo.ViewModel
{公共类FlickrPhotoViewModel：ViewModelBase
{
公共常量字符串ImageStreamPropertyName =的ImageStream; 专用流_imageStream = NULL; 公共流的ImageStream
{
得到
{
返回_imageStream;
} 组
{
如果（_imageStream ==值）
{
返回;
}
_imageStream =价值; RaisePropertyChanged（ImageStreamPropertyName）;
}
} 公共常量字符串IsLoadingPropertyName =IsLoading; 私人布尔_isLoading = FALSE; 公共BOOL IsLoading
{
得到
{
返回_isLoading;
} 组
{
如果（_isLoading ==值）
{
返回;
} _isLoading =价值; RaisePropertyChanged（IsLoadingPropertyName）;
}
} 公共常量字符串PhotoIDPropertyName =PHOTOID; 私人字符串_photoID =的String.Empty; 公共字符串PHOTOID
{
得到
{
返回_photoID;
} 组
{
如果（_photoID ==值）
{
返回;
} VAR属性oldValue = _photoID;
_photoID =价值; RaisePropertyChanged（PhotoIDPropertyName）;
}
} 公共FlickrPhotoViewModel（字符串PHOTOID）
{
this.PropertyChanged + =异步（S，E）=＆GT;
{
如果（e.PropertyName == ImageStreamPropertyName）
{
如果（！（的ImageStream == NULL ||的ImageStream == Stream.Null））
{
IsLoading = FALSE;
}
}
};
IsLoading = TRUE;
PHOTOID = PHOTOID;
}
}
}
解决方案问题是你的
的ImageStream属性的数据类型。有没有转换器，它知道如何处理空值的情况：的 System.Windows.Data错误：23：不能'从类型''转换为键入'System.Windows.Media.ImageSource'为'EN-US使用默认的转换文化; 考虑使用绑定的转换器属性的
解决这个问题的一种可能性是使自己的的IValueConverter 实施。如果输入的值是一个流返回。如果没有，返回null。如果这也不行，返回一个空的虚
的ImageSource。是这样的：
公共类ImageStreamForwardConverter：{的IValueConverter
公共对象转换（对象的值，类型TARGETTYPE，对象参数，CultureInfo的文化）{
如果（空==值）{
返回null;
}否则如果（价值流）{
返回值;
}其他{
抛出新的InvalidOperationException异常（不支持的类型）;
}
....I've got a scenario where I have Image Sources set to null which are resolved later and then displayed. Any good way to prevent my code from throwing binding errors?
An example:
System.Windows.Data Error: 23 : Cannot convert '' from type '' to type 'System.Windows.Media.ImageSource' for 'en-US' 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)'
Edit: By request
<Image x:Name="image" Height="Auto" Width="Auto" Opacity="0"> <Image.Effect> <DropShadowEffect/> </Image.Effect> <Image.Source> <Binding Path="ImageStream"> <Binding.ValidationRules> <validationRules:NotNullStreamValidationRule/> </Binding.ValidationRules> </Binding> </Image.Source> </Image> namespace FlickrDemo.ViewModel { public class FlickrPhotoViewModel : ViewModelBase { public const string ImageStreamPropertyName = "ImageStream"; private Stream _imageStream = null; public Stream ImageStream { get { return _imageStream; } set { if (_imageStream == value) { return; } _imageStream = value; RaisePropertyChanged(ImageStreamPropertyName); } } public const string IsLoadingPropertyName = "IsLoading"; private bool _isLoading = false; public bool IsLoading { get { return _isLoading; } set { if (_isLoading == value) { return; } _isLoading = value; RaisePropertyChanged(IsLoadingPropertyName); } } public const string PhotoIDPropertyName = "PhotoID"; private string _photoID = String.Empty; public string PhotoID { get { return _photoID; } set { if (_photoID == value) { return; } var oldValue = _photoID; _photoID = value; RaisePropertyChanged(PhotoIDPropertyName); } } public FlickrPhotoViewModel(string photoID) { this.PropertyChanged += async (s, e) => { if (e.PropertyName == ImageStreamPropertyName) { if (!(ImageStream == null || ImageStream == Stream.Null)) { IsLoading = false; } } }; IsLoading = true; PhotoID = photoID; } } }
解决方案The problem is the datatype of your
ImageStreamproperty. There is no converter that knows how to handle the null-situation:System.Windows.Data Error: 23 : Cannot convert '' from type '' to type 'System.Windows.Media.ImageSource' for 'en-US' culture with default conversions; consider using Converter property of Binding
One possibility to solve this problem is to make your own IValueConverter implementation. If the input value is a stream, return it. If not, return null. If this does not work, return an empty dummy
ImageSource.Something like:
public class ImageStreamForwardConverter : IValueConverter{ public object Convert(object value, Type targetType, object parameter, CultureInfo culture){ if(null == value){ return null; }else if(value is Stream){ return value; }else{ throw new InvalidOperationException("Unsupported type"); } ....
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