此视图不允许使用 WPF 'EditItem'

Question

我知道有很多关于该错误的问题（1、2、3、4、5等），但我找不到可以解释此错误原因并适合我的情况的问题。如果我错过了，请告诉我！

首先，我ItemsSource使用自定义类（不是ObservableCollection或任何其他 .NET 内置可观察集合）绑定到我的 DataGrid 。在向您展示它的代码之前，让我解释一下我的想法（我的假设可能是错误的）。

在我看来，要可绑定，集合必须至少实现IEnumerable和INotifyCollectionChanged。IEnumerable 以便视图获取要显示的项目（感谢该GetEnumerator方法）和 INotifyCollectionChanged 以便视图知道集合上的更改。

所以我最终上了这门课：

public class ObservableDictionary<TKey, TValue> : IDictionary<TKey, TValue>, IEnumerable<TValue>, INotifyCollectionChanged
{
    #region fields

    private IDictionary<TKey, TValue> _innerDictionary;

    #endregion

    #region properties

    public int Count { get { return _innerDictionary.Count; } }

    public ICollection<TKey> Keys { get { return _innerDictionary.Keys; } }

    public ICollection<TValue> Values { get { return _innerDictionary.Values; } }

    public bool IsReadOnly { get { return false; } }

    #endregion

    #region indexors

    public TValue this[TKey key]
    {
        get { return _innerDictionary[key]; }
        set { this.InternalAdd(new KeyValuePair<TKey, TValue>(key, value)); }
    }

    #endregion

    #region events

    public event NotifyCollectionChangedEventHandler CollectionChanged;

    #endregion

    #region constructors

    public ObservableDictionary()
    {
        _innerDictionary = new Dictionary<TKey, TValue>();
    }

    public ObservableDictionary(int capacity)
    {
        _innerDictionary = new Dictionary<TKey, TValue>(capacity);
    }

    public ObservableDictionary(IEqualityComparer<TKey> comparer)
    {
        _innerDictionary = new Dictionary<TKey, TValue>(comparer);
    }

    public ObservableDictionary(IDictionary<TKey, TValue> dictionary)
    {
        _innerDictionary = new Dictionary<TKey, TValue>(dictionary);
    }

    public ObservableDictionary(int capacity, IEqualityComparer<TKey> comparer)
    {
        _innerDictionary = new Dictionary<TKey, TValue>(capacity, comparer);
    }

    public ObservableDictionary(IDictionary<TKey, TValue> dictionary, IEqualityComparer<TKey> comparer)
    {
        _innerDictionary = new Dictionary<TKey, TValue>(dictionary, comparer);
    }

    #endregion

    #region public methods

    public bool ContainsKey(TKey key)
    {
        return _innerDictionary.ContainsKey(key);
    }

    public bool Contains(KeyValuePair<TKey, TValue> item)
    {
        return _innerDictionary.Contains(item);
    }

    public void Add(TKey key, TValue value)
    {
        this.InternalAdd(new KeyValuePair<TKey, TValue>(key, value));
    }

    public void AddRange(IEnumerable<KeyValuePair<TKey, TValue>> items)
    {
        if (!items.Any())
        {
            return;
        }

        var added = new List<TValue>();
        var removed = new List<TValue>();

        foreach (var item in items)
        {
            TValue value;
            if (_innerDictionary.TryGetValue(item.Key, out value))
            {
                removed.Add(value);
            }

            added.Add(item.Value);
            _innerDictionary[item.Key] = item.Value;
        }

        this.CollectionChanged?.Invoke(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, added, null));

        if (removed.Count > 0)
        {
            this.CollectionChanged?.Invoke(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, null, removed));
        }
    }

    public void Add(KeyValuePair<TKey, TValue> item)
    {
        this.InternalAdd(item);
    }

    public bool TryGetValue(TKey key, out TValue value)
    {
        return _innerDictionary.TryGetValue(key, out value);
    }

    public bool Remove(TKey key)
    {
        return this.InternalRemove(key);
    }

    public bool Remove(KeyValuePair<TKey, TValue> item)
    {
        return this.InternalRemove(item.Key);
    }

    public void Clear()
    {
        _innerDictionary.Clear();
        this.CollectionChanged?.Invoke(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
    }

    public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)
    {
        _innerDictionary.CopyTo(array, arrayIndex);
    }

    public IEnumerator<TValue> GetEnumerator()
    {
        return Values.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return this.GetEnumerator();
    }

    IEnumerator<KeyValuePair<TKey, TValue>> IEnumerable<KeyValuePair<TKey, TValue>>.GetEnumerator()
    {
        return _innerDictionary.GetEnumerator();
    }

    #endregion

    #region private methods

    /// <summary>
    /// Adds the specified value to the internal dictionary and indicates whether the element has actually been added. Fires the CollectionChanged event accordingly.
    /// </summary>
    /// <param name="key"></param>
    /// <param name="value"></param>
    private void InternalAdd(KeyValuePair<TKey, TValue> item)
    {
        IList added = new TValue[] { item.Value };

        TValue value;
        if (_innerDictionary.TryGetValue(item.Key, out value))
        {
            this.CollectionChanged?.Invoke(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, null, new TValue[] { value }));
        }

        _innerDictionary[item.Key] = item.Value;
        this.CollectionChanged?.Invoke(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, added, null));
    }

    /// <summary>
    /// Remove the specified key from the internal dictionary and indicates whether the element has actually been removed. Fires the CollectionChanged event accordingly.
    /// </summary>
    /// <param name="key"></param>
    /// <param name="value"></param>
    private bool InternalRemove(TKey key)
    {
        TValue value;
        if (_innerDictionary.TryGetValue(key, out value))
        {
            _innerDictionary.Remove(key);
            this.CollectionChanged?.Invoke(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, null, new TValue[] { value }));
        }

        return value != null;
    }

    #endregion
}

它隐式地IEnumerable<TValue>.GetEnumerator和显式地实现了其他GetEnumerator方法（IDictionary和IEnumerable），以便我的视图仅显示我的字典的值，并且我在CollectionChanged事件调用周围映射添加/删除方法。

我的 ViewModel 定义如下：

class MyViewModel
{
    public ObservableDictionary<string, Foo> Foos { get; private set; }

    public MyViewModel()
    {
        this.Foos = new ObservableDictionary<string, Foo>();
    }
}

并像这样将它绑定到我的视图：

<DataGrid ItemsSource="{Binding Facts}" AutoGenerateColumns="False" CanUserAddRows="False" CanUserDeleteRows="False">
    <DataGrid.Columns>
        <DataGridTextColumn Header="Name" Binding="{Binding Name}" IsReadOnly="True" Width="*" />
        <DataGridTextColumn Header="Type" Binding="{Binding Type}" IsReadOnly="True" Width="*" />
        <DataGridTextColumn Header="Value" Binding="{Binding Value}" IsReadOnly="False" Width="*" />
    </DataGrid.Columns>
</DataGrid>

然后，当我尝试编辑值时，出现指定的错误：

此视图不允许使用“EditItem”

当我在代码中放置一些断点时，我永远不会到达ObservableDictionaryindexor setter 或Foo.Valuesetter。

我对视图如何从绑定集合中获取项目的想法是否正确？为什么我会收到此错误和/或我如何授权我的视图EditItem？

Answer 1

如果您希望能够编辑数据，您的源集合类型 ( ObservableDictionary<TKey, TValue>) 应该实现该IList接口DataGrid。

每当您绑定到 WPF 中的某个集合属性时，您总是绑定到自动生成的视图，而不是实际的源集合本身。

运行时为您创建的视图类型取决于源集合的类型，并且您的源集合必须实现非通用IList接口才能使DataGrid控件的内部编辑功能正常工作。