c# - 如何提高自定义 BindingList 上 AddRange 方法的性能？

Question

我有一个自定义 BindingList，我想为其创建自定义 AddRange 方法。

public class MyBindingList<I> : BindingList<I>
{
    ...

    public void AddRange(IEnumerable<I> vals)
    {
        foreach (I v in vals)
            Add(v);
    }
}

我的问题是大型集合的性能很糟糕。我现在正在调试的案例是尝试添加大约 30,000 条记录，并且花费了无法接受的时间。

在线查看此问题后，问题似乎在于使用 Add 会在每次添加时调整数组的大小。 This answer我认为总结如下:

If you are using Add, it is resizing the inner array gradually as needed (doubling)

我可以在我的自定义 AddRange 实现中做什么来指定 BindingList 需要根据项目计数调整大小，而不是让它在添加每个项目时不断地重新分配数组？

Answer 1

CSharpie 在他的 answer 中解释道性能不佳是由于 ListChanged -事件在每个 Add 之后触发，并展示了一种实现方式 AddRange为您定制BindingList .

另一种方法是实现 AddRange作为 BindingList<T> 的扩展方法的功能.基于 CSharpies 实现:

/// <summary>
/// Extension methods for <see cref="System.ComponentModel.BindingList{T}"/>.
/// </summary>
public static class BindingListExtensions
{
  /// <summary>
  /// Adds the elements of the specified collection to the end of the <see cref="System.ComponentModel.BindingList{T}"/>,
  /// while only firing the <see cref="System.ComponentModel.BindingList{T}.ListChanged"/>-event once.
  /// </summary>
  /// <typeparam name="T">
  /// The type T of the values of the <see cref="System.ComponentModel.BindingList{T}"/>.
  /// </typeparam>
  /// <param name="bindingList">
  /// The <see cref="System.ComponentModel.BindingList{T}"/> to which the values shall be added.
  /// </param>
  /// <param name="collection">
  /// The collection whose elements should be added to the end of the <see cref="System.ComponentModel.BindingList{T}"/>.
  /// The collection itself cannot be null, but it can contain elements that are null,
  /// if type T is a reference type.
  /// </param>
  /// <exception cref="ArgumentNullException">values is null.</exception>
  public static void AddRange<T>(this System.ComponentModel.BindingList<T> bindingList, IEnumerable<T> collection)
  {
    // The given collection may not be null.
    if (collection == null)
      throw new ArgumentNullException(nameof(collection));

    // Remember the current setting for RaiseListChangedEvents
    // (if it was already deactivated, we shouldn't activate it after adding!).
    var oldRaiseEventsValue = bindingList.RaiseListChangedEvents;

    // Try adding all of the elements to the binding list.
    try
    {
      bindingList.RaiseListChangedEvents = false;

      foreach (var value in collection)
        bindingList.Add(value);
    }

    // Restore the old setting for RaiseListChangedEvents (even if there was an exception),
    // and fire the ListChanged-event once (if RaiseListChangedEvents is activated).
    finally
    {
      bindingList.RaiseListChangedEvents = oldRaiseEventsValue;

      if (bindingList.RaiseListChangedEvents)
        bindingList.ResetBindings();
    }
  }
}

这样，根据您的需要，您甚至可能不需要自己编写 BindingList -子类。