WPF绑定 - 为空字符串缺省值 [英] WPF Binding - Default value for empty string

问题描述

有没有设定一个WPF绑定如果绑定字符串是空的？

Is there a standard way to set a default or fallback value for a WPF binding if the bound string is empty?

<TextBlock Text="{Binding Name, FallbackValue='Unnamed'" />

的 FallbackValue 似乎只踢当名称为空，但不是当它被设置为的String.Empty 。

The FallbackValue only seems to kick in when Name is null, but not when it is set to String.Empty.

推荐答案

我是IM pression下的<一个href=\"http://msdn.microsoft.com/en-GB/library/system.windows.data.bindingbase.fallbackvalue.aspx\">FallbackValue提供一个值时，绑定失败，<一个href=\"http://msdn.microsoft.com/en-us/library/system.windows.data.bindingbase.targetnullvalue.aspx\">TargetNullValue提供一个值时，势必值为null。

I was under the impression that FallbackValue provides a value when the binding fails and TargetNullValue provides a value when the bound value is null.

要你想你要么需要一个转换器（可能带有参数）为空字符串转换为目标值，或将逻辑视图模型的东西。

To do what you want you will either need a converter (possibly with a parameter) to convert an empty string to a target value, or put the logic in your view model.

我可能会用一个转换器像这样（未测试）去了。

I would probably go with a converter something like this (not tested).

public class EmptyStringConverter : MarkupExtension, IValueConverter
{  
    public object Convert(object value, Type targetType, 
                          object parameter, CultureInfo culture)
    {
        return string.IsNullOrEmpty(value as string) ? parameter : value;
    }

    public object ConvertBack(object value, Type targetType, 
                              object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        return this;
    }
}

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