ObservableCollection 和 CollectionChanged 事件

Question

为什么下面的代码中没有触发 collectionchanged 事件，但我可以看到添加到 ObservableCollection 中的 InventoryBTO 的新实例？

 private ObservableCollection<InventoryBTO> _inventoryRecords;
    public ObservableCollection<InventoryBTO> InventoryRecords
    {
        get { return _inventoryRecords; }
        set { _inventoryRecords = value; }
    }

    private InventoryBTO _selectedRecord;
    public InventoryBTO SelectedRecord
    {
        get { return _selectedRecord; }
        set 
        {
            if (_selectedRecord != value)
            {
                _selectedRecord = value;
                OnPropertyChanged(new PropertyChangedEventArgs("SelectedRecord"));
            }
        }
    }

    public InventoryViewModel()
    {
        if (_inventoryRecords == null)
        {
            InventoryRecords = new ObservableCollection<InventoryBTO>();
            this.InventoryRecords.CollectionChanged += new NotifyCollectionChangedEventHandler(InventoryRecords_CollectionChanged);
        }

        _inventoryRecords = InventoryListBTO.GetAllInventoryRecords();
    }

    void InventoryRecords_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {

    } 

Answer 1

问题是您将私有成员分配给从方法返回的 ObservableCollection 的新实例。因此，发生的情况是，您连接到一个集合的事件，但随后删除该实例并将其替换为您从未连接过事件处理程序的新实例。这是你可以做的。创建一个继承自 ObservableCollection 的类并添加 addrange 方法：

public class RangeObservableCollection<T> : ObservableCollection<T>
{
    private bool supressEvents = false;

    public void AddRange(IEnumerable<T> items)
    {
        supressEvents = true;
        foreach (var item in items)
        {
            base.Add(item);
        }
        this.supressEvents = false;
        this.OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, items.ToList()));

    }

    protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        if (!this.surpressEvents)
        {
            base.OnCollectionChanged(e);
        }
    }
}

然后，您可以将您的类更改为：

private RangeObservableCollection<InventoryBTO> _inventoryRecords;
public RangeObservableCollection<InventoryBTO> InventoryRecords
{
    get { return _inventoryRecords; }
    set { _inventoryRecords = value; }
}

private InventoryBTO _selectedRecord;
public InventoryBTO SelectedRecord
{
    get { return _selectedRecord; }
    set 
    {
        if (_selectedRecord != value)
        {
            _selectedRecord = value;
            OnPropertyChanged(new PropertyChangedEventArgs("SelectedRecord"));
        }
    }
}

public InventoryViewModel()
{
    if (_inventoryRecords == null)
    {
        InventoryRecords = new ObservableCollection<InventoryBTO>();
        this.InventoryRecords.CollectionChanged += new NotifyCollectionChangedEventHandler(InventoryRecords_CollectionChanged);
    }

    this.InventoryRecords.AddRange(InventoryListBTO.GetAllInventoryRecords());
}

void InventoryRecords_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
    //e.NewItems will be an IList of all the items that were added in the AddRange method...
} 

Answer 2

尝试这个

public ObservableCollection<InventoryBTO> InventoryRecords
{
    get { return _inventoryRecords; }
    set 
    { 
      _inventoryRecords = value; 
      onPropertyChanged(this, "InventoryRecords");

    }
 }

或

public ObservableCollection<InventoryBTO> InventoryRecords
{
    get { return _inventoryRecords; }
    set 
    { 
      _inventoryRecords = value; 
      OnPropertyChanged(new PropertyChangedEventArgs("InventoryRecords"));

    }
 }

取决于您的实现。