WPF CollectionView Error: 'Collection was modified; enumeration operation may not execute.'

Question

我正在覆盖 System.Windows.Data.CollectionView 的行为。有一种方法应该从数据库中清除并重新填充 CollectionView.SourceCollection（在我的例子中是 ObservableCollection<object>）。抛出异常：

Exception thrown: 'System.InvalidOperationException' in mscorlib.dll

Additional information: Collection was modified; enumeration operation may not execute.

恰好在第二次命中此行时抛出 SourceObservableCollection.Add(item);。

（注释行描述了我解决问题的失败尝试）：

    //...
    public ObservableCollection<object> SourceObservableCollection { get { return (ObservableCollection<object>)SourceCollection; } }

    //<Part of Attempt7>
    protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs args)
    {
        base.OnCollectionChanged(args);
        isCollectionChanging = false;
    }
    private bool isCollectionChanging = false;
    //</Part of Attempt7>
    //<Part of Attempt9>
    private static readonly object _lock = new object();
    //</Part of Attempt9>
    //<*async syntax is part of Attempt10*/>
    public async void RefreshSource()
    {
        SourceObservableCollection.Clear();

        // refreshSourceFunction retrieves data from Database
        IEnumerable result = refreshSourceFunction(/*parameters*/);

        ////Attempt1:
        foreach (object item in result)
        {
            SourceObservableCollection.Add(item);
        }

        ////Attempt2:
        //foreach (object item in result.OfType<object>().ToList())
        //{
        //    SourceObservableCollection.Add(item);
        //}

        ////Attempt3:
        //List<object> lstResult = result.OfType<object>().ToList();
        //foreach (object item in lstResult)
        //    SourceObservableCollection.Add(item);

        ////Attempt4:
        //List<object> lstResult2 = result.OfType<object>().ToList();
        //for (int x = 0; x < lstResult2.Count; x++)
        //{
        //    SourceObservableCollection.Add(lstResult2[x]);
        //}

        ////Attempt5:
        //IEnumerator enumerator = result.GetEnumerator();
        //while (enumerator.MoveNext())
        //{
        //    SourceObservableCollection.Add(enumerator.Current);
        //}

        ////Attempt6:
        //IEnumerator enumerator2 = result.GetEnumerator();
        //while (enumerator2.MoveNext())
        //{
        //    Dispatcher.Invoke(() =>
        //    {
        //        SourceObservableCollection.Add(enumerator2.Current);
        //    });
        //}

        ////Attempt7:
        //foreach (object item in result)
        //{
        //    isCollectionChanging = true;
        //    Dispatcher.Invoke(() =>
        //    {
        //        SourceObservableCollection.Add(item);
        //    }, System.Windows.Threading.DispatcherPriority.Background);
        //    while (isCollectionChanging) ;
        //}

        ////Attempt8:
        //foreach (object item in result)
        //{
        //    SourceObservableCollection.Add(item);
        //    Refresh();
        //}

        ////Attempt9:
        //foreach (object item in result)
        //{
        //    lock (_lock)
        //    {
        //        SourceObservableCollection.Add(item);
        //    }
        //}

        ////Attempt10:
        //await Dispatcher.InvokeAsync(() => SourceObservableCollection.Clear());
        //IEnumerable result2 = await Task.Run(() => refreshSourceFunction(/*parameters*/));
        //foreach (object item in result2)
        //{
        //    await Dispatcher.InvokeAsync(() => SourceObservableCollection.Add(item));
        //}
    }
    //...

异常 StackTrace 只有这个：

at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)

但是，调试调用堆栈是：

mscorlib.dll!System.ThrowHelper.ThrowInvalidOperationException(System.ExceptionResource resource) Unknown

mscorlib.dll!System.Collections.Generic.List.Enumerator.MoveNextRare() Unknown

mscorlib.dll!System.Collections.Generic.List.Enumerator.MoveNext() Unknown

PresentationFramework.dll!MS.Internal.Data.IndexedEnumerable.EnsureEnumerator() Unknown

PresentationFramework.dll!MS.Internal.Data.IndexedEnumerable.EnsureCacheCurrent() Unknown

PresentationFramework.dll!MS.Internal.Data.IndexedEnumerable.Count.get() Unknown

PresentationFramework.dll!System.Windows.Data.CollectionView.Count.get() Unknown

PresentationFramework.dll!System.Windows.Data.CollectionView.AdjustCurrencyForAdd(int index) Unknown

PresentationFramework.dll!System.Windows.Data.CollectionView.ProcessCollectionChanged(System.Collections.Specialized.NotifyCollectionChangedEventArgs args) Unknown

PresentationFramework.dll!System.Windows.Data.CollectionView.OnCollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs args) Unknown

System.dll!System.Collections.ObjectModel.ObservableCollection.OnCollectionChanged(System.Collections.Specialized.NotifyCollectionChangedEventArgs e) Unknown

System.dll!System.Collections.ObjectModel.ObservableCollection.InsertItem(int index, System.__Canon item) Unknown

mscorlib.dll!System.Collections.ObjectModel.Collection.Add(object item) Unknown

MyDll.dll!MyDll.MyNamespace.MyOverriddenCollectionView.RefreshSource() Line 105 C#

观察调试堆栈跟踪后，我开始怀疑 MS.Internal.Data.IndexedEnumerable 方法，尤其是在 observing it in ReferenceSource 之后；如您所见，多线程使用是不安全的：

    /// <summary>
    /// for a collection implementing IEnumerable this offers
    /// optimistic indexer, i.e. this[int index] { get; }
    /// and cached Count/IsEmpty properties and IndexOf method,
    /// assuming that after an initial request to read item[N],
    /// the following indices will be a sequence for index N+1, N+2 etc.
    /// </summary>
    /// <remarks>
    /// This class is NOT safe for multi-threaded use.
    /// if the source collection implements IList or ICollection, the corresponding
    /// properties/methods will be used instead of the cached versions
    /// </remarks>
    internal class IndexedEnumerable : IEnumerable, IWeakEventListener
    {
    //...

但是，我仍然不知道如何解决这个问题，甚至不知道到底出了什么问题。任何帮助将不胜感激。

当前 .Net Framework 版本：4.5

Answer 1

当您迭代一个集合并尝试修改它时，会发生此异常。通常，当您遍历一个集合时，它 returns 一个 IEnumerable ，您可以将其假定为一个指针，依次向前移动。假设你改变了集合然后迭代器变得无效并且框架抛出无效操作异常

例如（伪代码）

Foreach(var item in collection)
{
    modify collection here; (Do some add , remove or clear operation)
}

上面的代码肯定会抛出异常

为了处理这种你必须遍历集合并想做一些修改操作的场景使用索引

例如（伪代码）

for(int i=0; i< collection.count(); i++)
{
    // do anything here
}

Answer 2

事实证明问题实际上出在 ObservableCollection<T> 本身，因为它不是线程安全的。它似乎在 UI 线程中被读取，同时它仍在被修改，并且问题中描述的与线程相关的解决方法不起作用，因为 CollectionChanged 事件正在无论如何提出。用线程安全版本 found here 替换类型 ObservableCollection<T> 解决了问题。

WPF CollectionView Error: 'Collection was modified; enumeration operation may not execute.'

WPF CollectionView Error: 'Collection was modified; enumeration operation may not execute.'

.net

c#

wpf

observablecollection

collectionview