IValueConverter 的最佳实践是什么？

Question

What is best practise for IValueConverter : Is it ok to put Exception in Convert method or should it return "something"?

Here is an example:

[ValueConversion(typeof(float), typeof(String))]
public class PercentConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == null || string.IsNullOrEmpty(value.ToString()))
            return string.Empty;

        if (value is float) //Edited to support CultureInfo.CurrentCulture,
            return string.Format(culture, "{0:n}{1}", ((float)value) * 100, "%");

        //** Is it ok to put Exception here or should I return "something" here? **
        throw new Exception("Can't convert from " + value.GetType().Name + ". Expected type if float.");
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException("Converting back is not implemented in " + this.GetType());
    }
}

Answer 1

If you fail to convert (malformed values, types, ...), return DependencyProperty.UnsetValue .

It indicates that the converter produced no value and that the binding uses the FallbackValue, if available, or the default value instead.

Also, you should convert data with culture-specific conversion or invariant conversions to be on the safe side.

Answer 2

I personally recommend using singleton converters. Then you don't have to create an instance at every usage site, but can reference the converter like this:

Converter={x:Static SomeNamespace:SomeConverter.Instance}

Answer 3

You've ignored CultureInfo while parsing the string.

Always take in to account the culture info passed otherwise it would always work on Thread's CurrentCulture.

I could give some thing like "7.34,123" as input, would your code work?