WPF绑定到Model对象列表的ViewModel列表

Question

在模型中,我有:

public ObservableCollection<Item> Items { get; private set; }

在ViewModel中,我有一个相应的ItemViewModel列表.我希望这个列表与模型列表双向绑定:

public ObservableCollection<ItemViewModel> ItemViewModels ...

在XAML中,我将绑定(在本例中为TreeView)到ItemViewModels属性.

我的问题是,上面显示的ViewModel中的"..."是什么？我希望一行或两行代码绑定这两个ObservableCollections(提供为每个模型对象构造的ViewModel的类型).但是,我担心的是需要一堆代码来处理Items.CollectionChanged事件并通过根据需要构建ViewModel来手动更新ItemViewModels列表,以及相应的相反方法,它将根据对ItemViewModel的更改来更新Items集合.

谢谢!

埃里克

Answer 1

您可以使用以下类:

public class BoundObservableCollection<T, TSource> : ObservableCollection<T>
{
    private ObservableCollection<TSource> _source;
    private Func<TSource, T> _converter;
    private Func<T, TSource, bool> _isSameSource;

    public BoundObservableCollection(
        ObservableCollection<TSource> source,
        Func<TSource, T> converter,
        Func<T, TSource, bool> isSameSource)
        : base()
    {
        _source = source;
        _converter = converter;
        _isSameSource = isSameSource;

        // Copy items
        AddItems(_source);

        // Subscribe to the source's CollectionChanged event
        _source.CollectionChanged += new System.Collections.Specialized.NotifyCollectionChangedEventHandler(_source_CollectionChanged);
    }

    private void AddItems(IEnumerable<TSource> items)
    {
        foreach (var sourceItem in items)
        {
            Add(_converter(sourceItem));
        }
    }

    void _source_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
    {
        switch (e.Action)
        {
            case NotifyCollectionChangedAction.Add:
                AddItems(e.NewItems.Cast<TSource>());
                break;
            case NotifyCollectionChangedAction.Move:
                // Not sure what to do here...
                break;
            case NotifyCollectionChangedAction.Remove:
                foreach (var sourceItem in e.OldItems.Cast<TSource>())
                {
                    var toRemove = this.First(item => _isSameSource(item, sourceItem));
                    this.Remove(toRemove);
                }
                break;
            case NotifyCollectionChangedAction.Replace:
                for (int i = e.NewStartingIndex; i < e.NewItems.Count; i++)
                {
                    this[i] = _converter((TSource)e.NewItems[i]);
                }
                break;
            case NotifyCollectionChangedAction.Reset:
                this.Clear();
                this.AddItems(_source);
                break;
            default:
                break;
        }
    }
}

使用方法如下:

var models = new ObservableCollection<Model>();
var viewModels =
    new BoundObservableCollection<ViewModel, Model>(
        models,
        m => new ViewModel(m), // creates a ViewModel from a Model
        (vm, m) => vm.Model.Equals(m)); // checks if the ViewModel corresponds to the specified model

在BoundObservableCollection将被更新时ObservableCollection会改变,但周围的其他方式(你就必须重写一些方法来做到这一点)