C# WPF 绑定 - 空字符串的默认值
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WPF Binding - Default value for empty string
提问by kroimon
Is there a standard way to set a default or fallback value for a WPF binding if the bound string is empty?
如果绑定字符串为空，是否有标准方法可以为 WPF 绑定设置默认值或回退值？
<TextBlock Text="{Binding Name, FallbackValue='Unnamed'" />
The FallbackValueonly seems to kick in when Nameis null, but not when it is set to String.Empty.
在FallbackValue似乎只踢的时候Name是空的，但不是当它被设置为String.Empty。
采纳答案by Phil
I was under the impression that FallbackValueprovides a value when the binding fails and TargetNullValueprovides a value when the bound value is null.
我的印象是，当绑定失败时FallbackValue提供一个值，而当绑定值为 null 时TargetNullValue提供一个值。
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.
要执行您想要的操作，您将需要一个转换器（可能带有参数）将空字符串转换为目标值，或者将逻辑放入您的视图模型中。
I would probably go with a converter something like this (not tested).
我可能会使用这样的转换器（未测试）。
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;
}
}
回答by Santux
You could use a converter and do the respective validation on it.
您可以使用转换器并对其进行相应的验证。
Binding="{Binding Path=Name, Converter={StaticResource nameToOtherNameConverter}}"
and in your converter
并在您的转换器中
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (!string.IsNullOrEmpty(value.ToString()))
{ /*do something and return your new value*/ }
回答by Viv
You should create a converter for this, which implements IValueConverter
您应该为此创建一个转换器，它实现 IValueConverter
public class StringEmptyConverter : IValueConverter {
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
return string.IsNullOrEmpty((string)value) ? parameter : value;
}
public object ConvertBack(
object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
throw new NotSupportedException();
}
}
Then in xaml you'd just provide the converter to the binding, (xxxjust represents your Window/ UserControl/ Style... where the binding is)
然后在XAML中你只需要提供转换器的结合，（xxx只是代表你Window/ UserControl/ Style...这里的绑定）
<xxx.Resources>
<local:StringEmptyConverter x:Key="StringEmptyConverter" />
</xxx.Resources>
<TextBlock Text="{Binding Name, Converter={StaticResource StringEmptyConverter}, ConverterParameter='Placeholder Text'}" />
回答by iltzortz
DataTriggeris the way i do it like this:
DataTrigger我这样做的方式是这样的：
<TextBox>
<TextBox.Style>
<Style TargetType="{x:Type TextBox}" BasedOn="{StaticResource ReadOnlyTextBox}">
<Setter Property="Text" Value="{Binding Name}"/>
<Style.Triggers>
<DataTrigger Binding="{Binding Path=Name.Length, FallbackValue=0, TargetNullValue=0}" Value="0">
<Setter Property="Text" Value="{x:Static local:ApplicationLabels.NoValueMessage}"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>
