通过转换器绑定到 ObservableCollection 的文本字符串未在集合更改时更新

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。问题是集合（它是一个 ObservableCollection）没有尝试更新文本，我可以说是因为 IValueConverter 中的调试点显示在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"/>

属性的 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

实现所需的一种可能性是将转换器逻辑包装到可重用行为中。

这是一个，它会像您的转换器一样工作，但只适用于 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 = ... ;
            };
        }));
}

这样使用：

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

TODO：添加空检查、取消订阅（如果绑定到持久的 ViewModel 属性可能会导致内存泄漏）、正确命名...

通过转换器绑定到 ObservableCollection 的文本字符串未在集合更改时更新

Text string bound to an ObservableCollection through a Converter not updating on collection change

c#

wpf

binding

observablecollection

ivalueconverter