通过转换器绑定到可观察集合的文本字符串不会在集合更改时更新

Question

我有一个非常简单的IValueConverter，可以将IList<string>转换为逗号分隔的字符串。麻烦的是集合(这是一个 ObservableCollection(没有尝试更新文本，我可以说，因为 IValueConverter 中的调试点显示加载初始绑定后没有调用它。

转换器(这部分在实际调用时似乎工作正常(

public class CollectionToCommaSeperatedString : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
if (value == null)
return parameter.ToString();
if (((IList<string>)value).Count > 0)
return String.Join(", ", ((IList<string>)value).ToArray()) ?? parameter.ToString();
else
return parameter.ToString();
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}

绑定元素：

<TextBlock Text="{Binding SelectedChannels, ConverterParameter='(Click to select channels)', Converter={StaticResource CollectionToCommaSeperatedString}, ElementName=userControl, Mode=OneWay}" HorizontalAlignment="Left" VerticalAlignment="Top"/>

该物业的 CB

：

public ObservableCollection<string> SelectedChannels
{
get { return (ObservableCollection<string>)GetValue(SelectedChannelsProperty); }
set { SetValue(SelectedChannelsProperty, value); }
}
public static readonly DependencyProperty SelectedChannelsProperty =
DependencyProperty.Register("SelectedChannels", typeof(ObservableCollection<string>), typeof(ChannelSelector), new PropertyMetadata(new ObservableCollection<string>()));

Answer 1

实现所需目的的一种可能性是将转换器逻辑包装成可重用的行为。

这是一个，它将按照您的转换器应该工作，但仅适用于TextBlock.Text：

public static class Behaviors
{
public static ObservableCollection<string> GetTest(DependencyObject obj) => (ObservableCollection<string>)obj.GetValue(TestProperty);
public static void SetTest(DependencyObject obj, ObservableCollection<string> value) => obj.SetValue(TestProperty, value);
public static readonly DependencyProperty TestProperty =
DependencyProperty.RegisterAttached("Test", typeof(ObservableCollection<string>), typeof(Behaviors), new PropertyMetadata(null, (d, e) =>
{
var textBlock = d as TextBlock;
var collection = e.NewValue as ObservableCollection<string>;
collection.CollectionChanged += (s, a) => 
{
// put logic here
textBlock.Text = ... ;
};
}));
}

像这样使用它：

<TextBlock local:Behaviors.Test="{Binding ...}" />

待办事项：添加空检查、取消订阅(如果绑定到持久 ViewModel 属性，可能会导致内存泄漏(、正确命名...