WPF如何绑定到DataContext存在? [英] wpf how to bind to DataContext existence?

问题描述

我在代码中动态设置了数据上下文.我希望根据是否DataContext == null启用/禁用屏幕上的按钮.当我分配DataContext时，我可以在代码中完成此操作，但如果可以像这样进行绑定，那就更好了:)

I set the datacontext dynamically in code. I would like a button on screen to be enabled/disabled depending if DataContext == null or not. I can do it in code when I assign the DataContext but it would be better if I can bind like that :)

推荐答案

当DataContext为null时，您应该能够在按钮样式上使用DataTrigger来禁用按钮.另一种选择是将IsEnabled属性绑定到DataContext，如果DataContext为null，则使用值转换器返回false，否则使用true.

You should be able to use a DataTrigger on the button style to disable your button when the DataContext is null. The other option is to bind the IsEnabled property to the DataContext and use a value converter to return false if DataContext is null and true otherwise.

带有触发器:

<Button>
   <Button.Style>
       <Style TargetType="{x:Type Button}">
          <Style.Triggers>
             <DataTrigger Binding="{Binding Path=DataContext, RelativeSource={RelativeSource Self}}" Value="{x:Null}">
                 <Setter Property="IsEnabled" Value="false"/>
             </DataTrigger>
          </Style.Triggers>
       </Style>
   </Button.Style>
</Button>

带有转换器:

转换器:

public class DataContextSetConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value != null;
    }

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

并使用它

<UserControl.Resources>
   <local:DataContextSetConverter x:Key="dataContextSetConverter"/>
</UserControl.Resources>

...

<Button IsEnabled="{Binding Path=DataContext, RelativeSource={RelativeSource Self}, Converter={StaticResource dataContextSetConverter}}"/>

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