你可以使用ValueConversionAttribute
来确定转换器中涉及的类型,并且可以有用地使用该信息。
请查看在WPF中使用管道值转换器,这是一个关于使用ValueConversionAttribute
的绝佳示例。
示例展示了如何链接多个转换器类,并且可以使用ValueConversion将类型信息传递给下一个转换器。
[ValueConversion( typeof( string ), typeof( ProcessingState ) )]
public class IntegerStringToProcessingStateConverter : IValueConverter
{
object IValueConverter.Convert(
object value, Type targetType, object parameter, CultureInfo culture )
{
int state;
bool numeric = Int32.TryParse( value as string, out state );
Debug.Assert( numeric, "value should be a String which contains a number" );
Debug.Assert( targetType.IsAssignableFrom( typeof( ProcessingState ) ),
"targetType should be ProcessingState" );
switch( state )
{
case -1:
return ProcessingState.Complete;
case 0:
return ProcessingState.Pending;
case +1:
return ProcessingState.Active;
}
return ProcessingState.Unknown;
}
object IValueConverter.ConvertBack(
object value, Type targetType, object parameter, CultureInfo culture )
{
throw new NotSupportedException( "ConvertBack not supported." );
}
}
[ValueConversion( typeof( ProcessingState ), typeof( Color ) )]
public class ProcessingStateToColorConverter : IValueConverter
{
object IValueConverter.Convert(
object value, Type targetType, object parameter, CultureInfo culture )
{
Debug.Assert(value is ProcessingState, "value should be a ProcessingState");
Debug.Assert( targetType == typeof( Color ), "targetType should be Color" );
switch( (ProcessingState)value )
{
case ProcessingState.Pending:
return Colors.Red;
case ProcessingState.Complete:
return Colors.Gold;
case ProcessingState.Active:
return Colors.Green;
}
return Colors.Transparent;
}
object IValueConverter.ConvertBack(
object value, Type targetType, object parameter, CultureInfo culture )
{
throw new NotSupportedException( "ConvertBack not supported." );
}
}
object IValueConverter.Convert(
object value, Type targetType, object parameter, CultureInfo culture )
{
object output = value;
for( int i = 0; i < this.Converters.Count; ++i )
{
IValueConverter converter = this.Converters[i];
Type currentTargetType = this.GetTargetType( i, targetType, true );
output = converter.Convert( output, currentTargetType, parameter, culture );
if( output == Binding.DoNothing )
break;
}
return output;
}
<!-- Converts the Status attribute text to a Color -->
<local:ValueConverterGroup x:Key="statusForegroundGroup">
<local:IntegerStringToProcessingStateConverter />
<local:ProcessingStateToColorConverter />
</local:ValueConverterGroup>