绑定到数组元素

Question

我正在尝试将TextBlock绑定到ObservableCollection中的特定元素.这就是我现在所做的:

private ObservableCollection<double> arr = new ObservableCollection<double>();
public ObservableCollection<double> Arr { get { return arr; } set { arr = value; }  }

testBox.DataContext = this;

private void Button_Click(object sender, RoutedEventArgs e)
{
   Arr[0] += 1.0;
}

    [ValueConversion(typeof(ObservableCollection<double>), typeof(String))]
    public class myObsCollConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            ObservableCollection<double> l = value as ObservableCollection<double>;
            if( l == null )
                return DependencyProperty.UnsetValue;
            int i = int.Parse(parameter.ToString());

            return l[i].ToString();
        }

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


    <Window.Resources>
        <local:myObsCollConverter x:Key="myConverter"/>
    </Window.Resources>

        <TextBlock Name="testBox" Text="{Binding Path=Arr,Converter={StaticResource myConverter}, ConverterParameter=0}" />

我看到的是testBox在创建时显示了Arr的第一个值.但它并没有反映出这个元素的任何变化.为了在textBox中看到Arr [0]的更改,我该怎么办？

Answer 1

无需转换器.你可以直接绑定到Arr[0]这样

 <TextBlock Name="testBox" Text="{Binding Path=Arr[0]}"/>

虽然为了动态更新,但是Arr需要实现这些元素INotifyPropertyChanged.

更新:详细说明:

public class MyDouble : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private double _Value;
    public double Value 
    { 
        get { return _Value; } 
        set { _Value = value; OnPropertyChanged("Value"); }
    }

    void OnPropertyChanged(string propertyName)
    {
       var handler = PropertyChanged;
       if (handler != null)
       {
          handler(this, new PropertyChangedEventArgs(propertyName));
       }
    }
}

然后

 ObservableCollection<MyDouble> Arr { get; set; }

并绑定到

 <TextBlock Name="testBox" Text="{Binding Path=Arr[0].Value}"/>

Answer 2

ObservableCollections不会将更改传播到存储在属于集合的对象中的值.它只会在集合本身的内容发生变化时触发通知(即添加,删除,重新排序项目).如果您想要在集合中的值发生更改时更新UI,那么您必须单独连接自己.