将项目添加到 ListCollectionView 时引发异常

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？

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：

在深入研究 .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 有私有方法ProcessCollectionChangedWithAdjustedIndex，它在不同的场景中调整索引，但在添加启用分组的新项目时不会调用它，我不知道为什么看起来这是设计使然（？！）所以你有为新项目手动指定占位符 AtBeginning。

Answer 2

我不确定，但我认为您应该使用AddNew() 方法而不是AddNewItem。你将调用CommitNew()，而不调用AddNew()，并且没有开始事务，所以抛出异常。

AddNewItem() 摘要：Adds the specified object to the collection.

AddNew() 摘要：Starts an add transaction and returns the pending new item.

CommitNew() 摘要：Ends the add transaction and saves the pending new item.

所以，你应该编写下一行代码：

Test pendingItem = (Test)collection2.AddNew();
pendingItem.Name = "Bob";
pendingItem.IsTrue = false;
collection2.CommitNew();