当在WPF创建的ViewModels有时需要在转换数据可用ObservableCollection （源集合）到延伸/限制/项目的原始元素（目标集合）包装元素的集合，而所述的数量和顺序元素总是反映原始集合。
就像选择扩展方法，不同之处在于它是不断更新的，因此可以用于WPF绑定。
如果一个元素在索引x添加到源中，相同的元件的封装在目标集合中的相同的索引x被加入。 如果在索引y中的元素的源集合中被移除时，在索引y中的元件在目标集合中被去除。
说有一个ObservableCollection<ClassA> ，但我需要绑定到是ReadOnlyObservableCollection<ClassB> （或等同物），其中ClassB - > ClassA如下：
class ClassB : INotifyPropertyChanged, IDisposable
{
public ClassB(ClassA a)
{
Wrapped = a;
(Wrapped as INotifyPropertyChanged).PropertyChanged+=WrappedChanged;
}
public ClassA Wrapped { get; private set; }
public int SomeOtherProperty { get { return SomeFunction(Wrapped); }
WrappedChanged(object s, NotifyPropertyChangedArgs a) { ... }
...
}
我可以写我自己的TemplatedTransformCollectionWrapper ，在那里我可以这样写：
ObservableCollection<ClassA> source;
TemplatedTransformCollectionWrapper theCollectionThatWillBeUsedInABinding
= TemplatedTransformCollectionWrapper(source, classA => new ClassB(classA));
TemplatedTransformCollectionWrapper理想的包装实现所有集合INotifyCollectionChanged和正确处理所有可能的添加，删除，替换原来，包裹，收集的操作。
这是不平凡的写TemplatedTransformCollectionWrapper正确，它似乎是那种别人已经做过的事情，也许它的核心框架的一部分，甚至。 但我不能找到它。
我张贴我的解决办法 - 这是一个自定义类 - 在这里。 仍然希望更好的答案。
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Collections.Specialized;
using System.Linq;
namespace ViewLayer
{
public class TransformObservableCollection<T,Source> : INotifyCollectionChanged, IList, IReadOnlyList<T>, IDisposable
{
public TransformObservableCollection(ObservableCollection<Source> wrappedCollection, Func<Source,T> transform)
{
m_WrappedCollection = wrappedCollection;
m_TransformFunc = transform;
((INotifyCollectionChanged)m_WrappedCollection).CollectionChanged += TransformObservableCollection_CollectionChanged;
m_TransformedCollection = new ObservableCollection<T>(m_WrappedCollection.Select(m_TransformFunc));
}
public void Dispose()
{
if (m_WrappedCollection == null) return;
((INotifyCollectionChanged)m_WrappedCollection).CollectionChanged -= TransformObservableCollection_CollectionChanged;
m_WrappedCollection = null;
}
void TransformObservableCollection_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
if (e.NewItems == null || e.NewItems.Count != 1)
break;
m_TransformedCollection.Insert(e.NewStartingIndex,m_TransformFunc((Source)e.NewItems[0]));
return;
case NotifyCollectionChangedAction.Move:
if (e.NewItems == null || e.NewItems.Count != 1 || e.OldItems == null || e.OldItems.Count != 1)
break;
m_TransformedCollection.Move(e.OldStartingIndex, e.NewStartingIndex);
return;
case NotifyCollectionChangedAction.Remove:
if (e.OldItems == null || e.OldItems.Count != 1)
break;
m_TransformedCollection.RemoveAt(e.OldStartingIndex);
return;
case NotifyCollectionChangedAction.Replace:
if (e.NewItems == null || e.NewItems.Count != 1 || e.OldItems == null || e.OldItems.Count != 1 || e.OldStartingIndex != e.NewStartingIndex)
break;
m_TransformedCollection[e.OldStartingIndex] = m_TransformFunc((Source)e.NewItems[0]);
return;
} // This is most likely called on a Clear(), we don't optimize the other cases (yet)
m_TransformedCollection.Clear();
foreach (var item in m_WrappedCollection)
m_TransformedCollection.Add(m_TransformFunc(item));
}
#region IList Edit functions that are unsupported because this collection is read only
public int Add(object value) { throw new InvalidOperationException(); }
public void Clear() { throw new InvalidOperationException(); }
public void Insert(int index, object value) { throw new InvalidOperationException(); }
public void Remove(object value) { throw new InvalidOperationException(); }
public void RemoveAt(int index) { throw new InvalidOperationException(); }
#endregion IList Edit functions that are unsupported because this collection is read only
#region Accessors
public T this[int index] { get { return m_TransformedCollection[index]; } }
object IList.this[int index] { get { return m_TransformedCollection[index]; } set { throw new InvalidOperationException(); } }
public bool Contains(T value) { return m_TransformedCollection.Contains(value); }
bool IList.Contains(object value) { return ((IList)m_TransformedCollection).Contains(value); }
public int IndexOf(T value) { return m_TransformedCollection.IndexOf(value); }
int IList.IndexOf(object value) { return ((IList)m_TransformedCollection).IndexOf(value); }
public int Count { get { return m_TransformedCollection.Count; } }
public IEnumerator<T> GetEnumerator() { return m_TransformedCollection.GetEnumerator(); }
IEnumerator IEnumerable.GetEnumerator() { return ((IEnumerable)m_TransformedCollection).GetEnumerator(); }
#endregion Accessors
public bool IsFixedSize { get { return false; } }
public bool IsReadOnly { get { return true; } }
public void CopyTo(Array array, int index) { ((IList)m_TransformedCollection).CopyTo(array, index); }
public void CopyTo(T[] array, int index) { m_TransformedCollection.CopyTo(array, index); }
public bool IsSynchronized { get { return false; } }
public object SyncRoot { get { return m_TransformedCollection; } }
ObservableCollection<T> m_TransformedCollection;
ObservableCollection<Source> m_WrappedCollection;
Func<Source, T> m_TransformFunc;
event NotifyCollectionChangedEventHandler INotifyCollectionChanged.CollectionChanged
{
add { ((INotifyCollectionChanged)m_TransformedCollection).CollectionChanged += value; }
remove { ((INotifyCollectionChanged)m_TransformedCollection).CollectionChanged -= value; }
}
}
}
