如果不为null,则NullToVisibilityConverter变为可见

Question

想要在listview中隐藏和显示SelectedItem的属性网格

<UserControl xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"
      <ListView>
         <!--here is list view-->
      </ListView>
      <xctk:PropertyGrid SelectedObject="{Binding Active}" Visibility="{Binding Active, Converter=NullToVisibilityConverter}" >  
   </xctk:PropertyGrid>
</UserControl>

所以我需要转换器并在可见性属性转换器中使用它.有帮助吗？

Answer 1

public class NullVisibilityConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value == null ? Visibility.Hidden : Visibility.Visible;
    }

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

然后在XAML资源中引用NullVisibilityConverter.

<StackPanel.Resources>
  <simpleXamlContent:NullVisibilityConverter x:Key="NullToVisibilityConverter"/>
</StackPanel.Resources>

Answer 2

要使用转换器，我们可以在资源中创建一个，并在绑定语句中将其称为静态资源。

<UserControl xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit">
    <UserControl.Resources>
      <yournamespace:NullVisibilityConverter x:Key="NullToVisibilityConverter"/>
    </UserControl.Resources>

    <ListView>
    <!--here is list view-->
    </ListView>

    <xctk:PropertyGrid SelectedObject="{Binding Active}" Visibility="{Binding Active, Converter={StaticResource NullToVisibilityConverter}}" >  
    </xctk:PropertyGrid>
</UserControl>

和Converter类本身

public class NullVisibilityConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value == null ? Visibility.Hidden : Visibility.Visible;
    }

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

Answer 3

有一些更有用的版本允许设置默认的不可见值：

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
    string defaultInvisibility = parameter as string;
    Visibility invisibility = (defaultInvisibility != null) ?
        (Visibility)Enum.Parse(typeof(Visibility), defaultInvisibility)
        : Visibility.Collapsed;
    return value == null ? invisibility : Visibility.Visible;
}

public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
    return DependencyProperty.UnsetValue;
}

在资源中的任何位置添加：

<converters:NullReferenceToVisibilityConverter x:Key="NullToVis" />

并像这样使用它：

<StackPanel Visibility="{Binding MyObject, Converter={StaticResource NullToVis}}">
<StackPanel Visibility="{Binding MyObject, Converter={StaticResource NullToVis}, ConverterParameter=Hidden}">