c# - 将项目添加到 ListCollectionView 时抛出异常

Question

当我运行以下测试时，我得到一个 ArgumentOutOfRangeException:

[TestClass]
public class ReproduceException
{
    [TestMethod]
    public void Doesnt_throw_when_adding_to_grouped_collection()
    {
        var collection = new ListCollectionView(new List<Test>());
        collection.SortDescriptions.Add(new SortDescription("IsTrue", ListSortDirection.Ascending));
        collection.GroupDescriptions.Add(new PropertyGroupDescription("Name"));
        collection.AddNewItem(new Test() { Name = "Bob", IsTrue = false });
        collection.CommitNew();

    }
}

public class Test
{
    public string Name { get; set; }
    public bool IsTrue { get; set; }
}

我得到以下异常:

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
at System.ThrowHelper.ThrowArgumentOutOfRangeException()
at System.Collections.ObjectModel.Collection`1.RemoveAt(Int32 index)
at System.Windows.Data.ListCollectionView.CommitNewForGrouping()
at System.Windows.Data.ListCollectionView.CommitNew()

我可能没有以正确的方式使用 AddNewItem/CommitNew 吗？

Answer 1

可能的解决方案:

1)在添加新项目之前做

 collection.NewItemPlaceholderPosition = NewItemPlaceholderPosition.AtBeginning;

2) 基本上尝试在创建分组和排序之前添加项目:

var collection = new ListCollectionView(new List<Test>());            
collection.AddNewItem(new Test() { Name = "Bob", IsTrue = false });
collection.CommitNew();

collection.SortDescriptions.Add(new SortDescription("IsTrue", 
                                          ListSortDirection.Ascending));   
collection.GroupDescriptions.Add(new PropertyGroupDescription("Name"));

分析:

深入研究 .NET Reflector 后，CommitNew() 方法有以下检查:

// !!! When you've added GroupDescription this.IsGrouping becomes true!
if (this.IsGrouping)
{
    this.CommitNewForGrouping();
}

由于您已经添加了 GroupDescription，它将提交分组:

private void CommitNewForGrouping()
{
    int num;   

    // !!! I believe it is None by default
    switch (this.NewItemPlaceholderPosition)
    {
        case NewItemPlaceholderPosition.AtBeginning:
            num = 1;
            break;

        case NewItemPlaceholderPosition.AtEnd:
            num = this._group.Items.Count - 2;
            break;

        default:
            // !!! Since you've not added groups -1 would be assigned to num
            num = this._group.Items.Count - 1;
            break;
    }
    int index = this._newItemIndex;
    object item = this.EndAddNew(false);

    // This method will call RemoveAt(num) where num == -1 in your case
    this._group.RemoveSpecialItem(num, item, false);
    this.ProcessCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, 
             item, index));

}

internal void RemoveSpecialItem(int index, object item, bool loading)
{
     ...
     // will fail since index always -1
     base.ProtectedItems.RemoveAt(index);
     ...
}

LCV 有私有(private)方法 ProcessCollectionChangedWithAdjustedIndex 可以在不同情况下调整索引，但在添加启用分组的新项目时不会调用它，我不确定为什么看起来像这样是设计使然(？ !) 因此您必须为新项目手动指定占位符 AtBeginning。