UICollectionView - 在一个视图上更新动画太多(UICollectionView - too many update animations on one view)

 更新：解决了！ 请参阅下面的答案以获得解决方案。 
 
 我的应用程序在UICollectionView中显示了许多图像。 当新项目插入太快而集合视图无法处理时，我目前遇到insertItemsAtIndexPaths问题。 以下是例外情况： 
 
 
 
 NSInternalInconsistencyException原因：在一个视图上更新动画太多 - 一次飞行限制为31 
 
 
 事实证明这是由于我的模型缓冲了多达20个新图像并立即将它们推送到数据源但不在集合视图批量更新块中。 没有批量更新不是由于我的懒惰造成的，而是因为我的数据源之间的抽象层实际上是一个.Net Observable集合（下面的代码）。 
 
 我想知道的是开发人员如何防止在飞行中达到31个动画的硬编码限制？ 我的意思是当它发生时，你是敬酒。 那么Apple的想法是什么？ 
 
 Monotouch开发人员阅读代码的注意事项： 
 
 崩溃实际上是由UICollectionViewDataSourceFlatReadOnly压倒UIDataBoundCollectionView并使用CollectionChanged事件引起的，它代表底层的observable集合代理控件。 这导致collectionview受到非批量InsertItems调用的打击。 （是保罗，它是一个ReactiveCollection）。 
 
 UIDataBoundCollectionView 
 
/// <summary>
/// UITableView subclass that supports automatic updating in response 
/// to DataSource changes if the DataSource supports INotifiyCollectionChanged
/// </summary>
[Register("UIDataBoundCollectionView")]
public class UIDataBoundCollectionView : UICollectionView,
  IEnableLogger
{
  public override NSObject WeakDataSource
  {
    get
    {
      return base.WeakDataSource;
    }

    set
    {
      var ncc = base.WeakDataSource as INotifyCollectionChanged;
      if(ncc != null)
      {
        ncc.CollectionChanged -= OnDataSourceCollectionChanged;
      }

      base.WeakDataSource = value;

      ncc = base.WeakDataSource as INotifyCollectionChanged;
      if(ncc != null)
      {
        ncc.CollectionChanged += OnDataSourceCollectionChanged;
      }
    }
  }

  void OnDataSourceCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
  {
    NSIndexPath[] indexPaths;

    switch(e.Action)
    {
      case NotifyCollectionChangedAction.Add:
        indexPaths = IndexPathHelper.FromRange(e.NewStartingIndex, e.NewItems.Count);
        InsertItems(indexPaths);
        break;

      case NotifyCollectionChangedAction.Remove:
        indexPaths = IndexPathHelper.FromRange(e.OldStartingIndex, e.OldItems.Count);
        DeleteItems(indexPaths);
        break;

      case NotifyCollectionChangedAction.Replace:
      case NotifyCollectionChangedAction.Move:
        PerformBatchUpdates(() =>
        {
          for(int i=0; i<e.OldItems.Count; i++)
            MoveItem(NSIndexPath.FromItemSection(e.OldStartingIndex + i, 0), NSIndexPath.FromItemSection(e.NewStartingIndex + i, 0));
        }, null);
        break;

      case NotifyCollectionChangedAction.Reset:
        ReloadData();
        break;
    }
  }
}
 
 UICollectionViewDataSourceFlatReadOnly 
 
/// <summary>
/// Binds a table to an flat (non-grouped) items collection 
/// Supports dynamically changing collections through INotifyCollectionChanged 
/// </summary>
public class UICollectionViewDataSourceFlatReadOnly : UICollectionViewDataSource,
  ICollectionViewDataSource,
  INotifyCollectionChanged
{
  /// <summary>
  /// Initializes a new instance of the <see cref="UICollectionViewDataSourceFlat"/> class.
  /// </summary>
  /// <param name="table">The table.</param>
  /// <param name="items">The items.</param>
  /// <param name="cellProvider">The cell provider</param>
  public UICollectionViewDataSourceFlatReadOnly(IReadOnlyList<object> items, ICollectionViewCellProvider cellProvider)
  {
    this.items = items;
    this.cellProvider = cellProvider;

    // wire up proxying collection changes if supported by source
    var ncc = items as INotifyCollectionChanged;
    if(ncc != null)
    {
      // wire event handler
      ncc.CollectionChanged += OnItemsChanged;
    }
  }

  #region Properties
  private IReadOnlyList<object> items;
  private readonly ICollectionViewCellProvider cellProvider;
  #endregion

  #region Overrides of UICollectionViewDataSource

  public override int NumberOfSections(UICollectionView collectionView)
  {
    return 1;
  }

  public override int GetItemsCount(UICollectionView collectionView, int section)
  {
    return items.Count;
  }

  /// <summary>
  /// Gets the cell.
  /// </summary>
  /// <param name="tableView">The table view.</param>
  /// <param name="indexPath">The index path.</param>
  /// <returns></returns>
  public override UICollectionViewCell GetCell(UICollectionView collectionView, NSIndexPath indexPath)
  {
    // reuse or create new cell
    var cell = (UICollectionViewCell) collectionView.DequeueReusableCell(cellProvider.Identifier, indexPath);

    // get the associated collection item
    var item = GetItemAt(indexPath);

    // update the cell
    if(item != null)
      cellProvider.UpdateCell(cell, item, collectionView.GetIndexPathsForSelectedItems().Contains(indexPath));

    // done
    return cell;
  }

  #endregion

  #region Implementation of ICollectionViewDataSource

  /// <summary>
  /// Gets the item at.
  /// </summary>
  /// <param name="indexPath">The index path.</param>
  /// <returns></returns>
  public object GetItemAt(NSIndexPath indexPath)
  {
    return items[indexPath.Item];
  }

  public int ItemCount
  {
    get
    {
      return items.Count;
    }
  }

  #endregion

  #region INotifyCollectionChanged implementation

  // UIDataBoundCollectionView will subscribe to this event
  public event NotifyCollectionChangedEventHandler CollectionChanged;

  #endregion

  void OnItemsChanged(object sender, NotifyCollectionChangedEventArgs e)
  {
    if(CollectionChanged != null)
      CollectionChanged(sender, e);
  }
}

Update: Solved! See my answer below for the solution.
 
My app displays a number of images in a UICollectionView. And I'm currently experiencing a problem with insertItemsAtIndexPaths when new items are getting inserted too fast for the collection view to handle. Below is the exception:
 
 
 
NSInternalInconsistencyException Reason: too many update animations on one view - limit is 31 in flight at a time
 
 
Turns out this was caused by my model buffering up to 20 new images and pushing them to the datasource at once but not inside a collection view batch update block. The absence of the batch update is not caused by laziness on my part but because of an abstraction layer between my datasource which is actually a .Net Observable collection (code below).
 
What I would like to know is how is the developer supposed to prevent hitting the hard coded limit of 31 animations in flight? I mean when it happens, you are toast. So what was Apple thinking?
 
Note to Monotouch Developers reading the code:
 
The crash is effectively caused by the UICollectionViewDataSourceFlatReadOnly overwhelming UIDataBoundCollectionView with CollectionChanged events which it proxies to the control on behalf of the underlying observable collection. Which results in the collectionview getting hammered with non-batched InsertItems calls. (yes Paul, its a ReactiveCollection).
 
UIDataBoundCollectionView
 
/// <summary>
/// UITableView subclass that supports automatic updating in response 
/// to DataSource changes if the DataSource supports INotifiyCollectionChanged
/// </summary>
[Register("UIDataBoundCollectionView")]
public class UIDataBoundCollectionView : UICollectionView,
  IEnableLogger
{
  public override NSObject WeakDataSource
  {
    get
    {
      return base.WeakDataSource;
    }

    set
    {
      var ncc = base.WeakDataSource as INotifyCollectionChanged;
      if(ncc != null)
      {
        ncc.CollectionChanged -= OnDataSourceCollectionChanged;
      }

      base.WeakDataSource = value;

      ncc = base.WeakDataSource as INotifyCollectionChanged;
      if(ncc != null)
      {
        ncc.CollectionChanged += OnDataSourceCollectionChanged;
      }
    }
  }

  void OnDataSourceCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
  {
    NSIndexPath[] indexPaths;

    switch(e.Action)
    {
      case NotifyCollectionChangedAction.Add:
        indexPaths = IndexPathHelper.FromRange(e.NewStartingIndex, e.NewItems.Count);
        InsertItems(indexPaths);
        break;

      case NotifyCollectionChangedAction.Remove:
        indexPaths = IndexPathHelper.FromRange(e.OldStartingIndex, e.OldItems.Count);
        DeleteItems(indexPaths);
        break;

      case NotifyCollectionChangedAction.Replace:
      case NotifyCollectionChangedAction.Move:
        PerformBatchUpdates(() =>
        {
          for(int i=0; i<e.OldItems.Count; i++)
            MoveItem(NSIndexPath.FromItemSection(e.OldStartingIndex + i, 0), NSIndexPath.FromItemSection(e.NewStartingIndex + i, 0));
        }, null);
        break;

      case NotifyCollectionChangedAction.Reset:
        ReloadData();
        break;
    }
  }
}
 
UICollectionViewDataSourceFlatReadOnly
 
/// <summary>
/// Binds a table to an flat (non-grouped) items collection 
/// Supports dynamically changing collections through INotifyCollectionChanged 
/// </summary>
public class UICollectionViewDataSourceFlatReadOnly : UICollectionViewDataSource,
  ICollectionViewDataSource,
  INotifyCollectionChanged
{
  /// <summary>
  /// Initializes a new instance of the <see cref="UICollectionViewDataSourceFlat"/> class.
  /// </summary>
  /// <param name="table">The table.</param>
  /// <param name="items">The items.</param>
  /// <param name="cellProvider">The cell provider</param>
  public UICollectionViewDataSourceFlatReadOnly(IReadOnlyList<object> items, ICollectionViewCellProvider cellProvider)
  {
    this.items = items;
    this.cellProvider = cellProvider;

    // wire up proxying collection changes if supported by source
    var ncc = items as INotifyCollectionChanged;
    if(ncc != null)
    {
      // wire event handler
      ncc.CollectionChanged += OnItemsChanged;
    }
  }

  #region Properties
  private IReadOnlyList<object> items;
  private readonly ICollectionViewCellProvider cellProvider;
  #endregion

  #region Overrides of UICollectionViewDataSource

  public override int NumberOfSections(UICollectionView collectionView)
  {
    return 1;
  }

  public override int GetItemsCount(UICollectionView collectionView, int section)
  {
    return items.Count;
  }

  /// <summary>
  /// Gets the cell.
  /// </summary>
  /// <param name="tableView">The table view.</param>
  /// <param name="indexPath">The index path.</param>
  /// <returns></returns>
  public override UICollectionViewCell GetCell(UICollectionView collectionView, NSIndexPath indexPath)
  {
    // reuse or create new cell
    var cell = (UICollectionViewCell) collectionView.DequeueReusableCell(cellProvider.Identifier, indexPath);

    // get the associated collection item
    var item = GetItemAt(indexPath);

    // update the cell
    if(item != null)
      cellProvider.UpdateCell(cell, item, collectionView.GetIndexPathsForSelectedItems().Contains(indexPath));

    // done
    return cell;
  }

  #endregion

  #region Implementation of ICollectionViewDataSource

  /// <summary>
  /// Gets the item at.
  /// </summary>
  /// <param name="indexPath">The index path.</param>
  /// <returns></returns>
  public object GetItemAt(NSIndexPath indexPath)
  {
    return items[indexPath.Item];
  }

  public int ItemCount
  {
    get
    {
      return items.Count;
    }
  }

  #endregion

  #region INotifyCollectionChanged implementation

  // UIDataBoundCollectionView will subscribe to this event
  public event NotifyCollectionChangedEventHandler CollectionChanged;

  #endregion

  void OnItemsChanged(object sender, NotifyCollectionChangedEventArgs e)
  {
    if(CollectionChanged != null)
      CollectionChanged(sender, e);
  }
}

原文：https://stackoverflow.com/questions/19046423