平台：WPF, .NET 4.0, C# 4.0
问题：在Mainwindow.xaml中，我有一个ListBox绑定到Customer集合，该集合当前是一个ObservableCollection <Customer>。
ObservableCollection<Customer> c = new ObservableCollection<Customer>();
此集合可以通过多个源进行更新，如FileSystem，WebService等。
为了允许并行加载Customers，我创建了一个帮助类
public class CustomerManager(ref ObsevableCollection<Customer> cust)
内部为每个客户源生成一个新任务（来自并行扩展库），并将新的Customer实例添加到客户集合对象（由ref传递给它的ctor）。
问题是ObservableCollection <T>（或任何集合）不能在UI线程以外的调用中使用并遇到异常：
“NotSupportedException - 这种类型的CollectionView不支持从与Dispatcher线程不同的线程更改其SourceCollection。”
我试过用了
System.Collections.Concurrent.ConcurrentBag<Customer>
集合但它没有实现INotifyCollectionChanged接口。因此我的WPF UI不会自动更新。
那么，是否有一个集合类可以实现属性/集合更改通知，还允许来自其他非UI线程的调用？
通过我最初的bing /谷歌搜索，没有提供开箱即用。
编辑：我创建了自己的集合，它继承自ConcurrentBag <Customer>，并且还实现了INotifyCollectionChanged接口。但令我惊讶的是，即使在单独的任务中调用它之后，WPF UI也会挂起，直到任务完成。是不应该并行执行任务而不阻止UI线程？
提前感谢您的任何建议。
有两种可能的方法。第一种方法是从并发集合继承并添加INotifyCollectionChanged功能，第二种方法是从实现INotifyCollectionChanged的集合继承并添加并发支持。我认为将INotifyCollectionChanged支持添加到并发集合中要容易得多，也更安全。我的建议如下。
它看起来很长，但大多数方法只调用内部并发集合，就像调用者直接使用它一样。从集合中添加或删除的少数几个方法注入一个私有方法的调用，该方法在构造时提供的调度程序上引发通知事件，从而允许该类是线程安全的，但确保在同一个线程上引发通知所有时间。
using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Runtime.InteropServices;
using System.Security.Permissions;
using System.Windows.Threading;
namespace Collections
{
/// <summary>
/// Concurrent collection that emits change notifications on a dispatcher thread
/// </summary>
/// <typeparam name="T">The type of objects in the collection</typeparam>
[Serializable]
[ComVisible(false)]
[HostProtection(SecurityAction.LinkDemand, Synchronization = true, ExternalThreading = true)]
public class ObservableConcurrentBag<T> : IProducerConsumerCollection<T>,
IEnumerable<T>, ICollection, IEnumerable
{
/// <summary>
/// The dispatcher on which event notifications will be raised
/// </summary>
private readonly Dispatcher dispatcher;
/// <summary>
/// The internal concurrent bag used for the 'heavy lifting' of the collection implementation
/// </summary>
private readonly ConcurrentBag<T> internalBag;
/// <summary>
/// Initializes a new instance of the ConcurrentBag<T> class that will raise <see cref="INotifyCollectionChanged"/> events
/// on the specified dispatcher
/// </summary>
public ObservableConcurrentBag(Dispatcher dispatcher)
{
this.dispatcher = dispatcher;
this.internalBag = new ConcurrentBag<T>();
}
/// <summary>
/// Initializes a new instance of the ConcurrentBag<T> class that contains elements copied from the specified collection
/// that will raise <see cref="INotifyCollectionChanged"/> events on the specified dispatcher
/// </summary>
public ObservableConcurrentBag(Dispatcher dispatcher, IEnumerable<T> collection)
{
this.dispatcher = dispatcher;
this.internalBag = new ConcurrentBag<T>(collection);
}
/// <summary>
/// Occurs when the collection changes
/// </summary>
public event NotifyCollectionChangedEventHandler CollectionChanged;
/// <summary>
/// Raises the <see cref="CollectionChanged"/> event on the <see cref="dispatcher"/>
/// </summary>
private void RaiseCollectionChangedEventOnDispatcher(NotifyCollectionChangedEventArgs e)
{
this.dispatcher.BeginInvoke(new Action<NotifyCollectionChangedEventArgs>(this.RaiseCollectionChangedEvent), e);
}
/// <summary>
/// Raises the <see cref="CollectionChanged"/> event
/// </summary>
/// <remarks>
/// This method must only be raised on the dispatcher - use <see cref="RaiseCollectionChangedEventOnDispatcher" />
/// to do this.
/// </remarks>
private void RaiseCollectionChangedEvent(NotifyCollectionChangedEventArgs e)
{
this.CollectionChanged(this, e);
}
#region Members that pass through to the internal concurrent bag but also raise change notifications
bool IProducerConsumerCollection<T>.TryAdd(T item)
{
bool result = ((IProducerConsumerCollection<T>)this.internalBag).TryAdd(item);
if (result)
{
this.RaiseCollectionChangedEventOnDispatcher(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, item));
}
return result;
}
public void Add(T item)
{
this.internalBag.Add(item);
this.RaiseCollectionChangedEventOnDispatcher(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, item));
}
public bool TryTake(out T item)
{
bool result = this.TryTake(out item);
if (result)
{
this.RaiseCollectionChangedEventOnDispatcher(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, item));
}
return result;
}
#endregion
#region Members that pass through directly to the internal concurrent bag
public int Count
{
get
{
return this.internalBag.Count;
}
}
public bool IsEmpty
{
get
{
return this.internalBag.IsEmpty;
}
}
bool ICollection.IsSynchronized
{
get
{
return ((ICollection)this.internalBag).IsSynchronized;
}
}
object ICollection.SyncRoot
{
get
{
return ((ICollection)this.internalBag).SyncRoot;
}
}
IEnumerator<T> IEnumerable<T>.GetEnumerator()
{
return ((IEnumerable<T>)this.internalBag).GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return ((IEnumerable)this.internalBag).GetEnumerator();
}
public T[] ToArray()
{
return this.internalBag.ToArray();
}
void IProducerConsumerCollection<T>.CopyTo(T[] array, int index)
{
((IProducerConsumerCollection<T>)this.internalBag).CopyTo(array, index);
}
void ICollection.CopyTo(Array array, int index)
{
((ICollection)this.internalBag).CopyTo(array, index);
}
#endregion
}
}
请查看Caliburn.Micro图书馆的BindableCollection<T>：
/// <summary>
/// A base collection class that supports automatic UI thread marshalling.
/// </summary>
/// <typeparam name="T">The type of elements contained in the collection.</typeparam>
#if !SILVERLIGHT && !WinRT
[Serializable]
#endif
public class BindableCollection<T> : ObservableCollection<T>, IObservableCollection<T> {
/// <summary>
/// Initializes a new instance of the <see cref = "Caliburn.Micro.BindableCollection{T}" /> class.
/// </summary>
public BindableCollection() {
IsNotifying = true;
}
/// <summary>
/// Initializes a new instance of the <see cref = "Caliburn.Micro.BindableCollection{T}" /> class.
/// </summary>
/// <param name = "collection">The collection from which the elements are copied.</param>
/// <exception cref = "T:System.ArgumentNullException">
/// The <paramref name = "collection" /> parameter cannot be null.
/// </exception>
public BindableCollection(IEnumerable<T> collection) : base(collection) {
IsNotifying = true;
}
#if !SILVERLIGHT && !WinRT
[field: NonSerialized]
#endif
bool isNotifying; //serializator try to serialize even autogenerated fields
/// <summary>
/// Enables/Disables property change notification.
/// </summary>
#if !WinRT
[Browsable(false)]
#endif
public bool IsNotifying {
get { return isNotifying; }
set { isNotifying = value; }
}
/// <summary>
/// Notifies subscribers of the property change.
/// </summary>
/// <param name = "propertyName">Name of the property.</param>
#if WinRT || NET45
public virtual void NotifyOfPropertyChange([CallerMemberName]string propertyName = "") {
#else
public virtual void NotifyOfPropertyChange(string propertyName) {
#endif
if(IsNotifying)
Execute.OnUIThread(() => OnPropertyChanged(new PropertyChangedEventArgs(propertyName)));
}
/// <summary>
/// Raises a change notification indicating that all bindings should be refreshed.
/// </summary>
public void Refresh() {
Execute.OnUIThread(() => {
OnPropertyChanged(new PropertyChangedEventArgs("Count"));
OnPropertyChanged(new PropertyChangedEventArgs("Item[]"));
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
});
}
/// <summary>
/// Inserts the item to the specified position.
/// </summary>
/// <param name = "index">The index to insert at.</param>
/// <param name = "item">The item to be inserted.</param>
protected override sealed void InsertItem(int index, T item) {
Execute.OnUIThread(() => InsertItemBase(index, item));
}
/// <summary>
/// Exposes the base implementation of the <see cref = "InsertItem" /> function.
/// </summary>
/// <param name = "index">The index.</param>
/// <param name = "item">The item.</param>
/// <remarks>
/// Used to avoid compiler warning regarding unverifiable code.
/// </remarks>
protected virtual void InsertItemBase(int index, T item) {
base.InsertItem(index, item);
}
#if NET || WP8 || WinRT
/// <summary>
/// Moves the item within the collection.
/// </summary>
/// <param name="oldIndex">The old position of the item.</param>
/// <param name="newIndex">The new position of the item.</param>
protected sealed override void MoveItem(int oldIndex, int newIndex) {
Execute.OnUIThread(() => MoveItemBase(oldIndex, newIndex));
}
/// <summary>
/// Exposes the base implementation fo the <see cref="MoveItem"/> function.
/// </summary>
/// <param name="oldIndex">The old index.</param>
/// <param name="newIndex">The new index.</param>
/// <remarks>Used to avoid compiler warning regarding unverificable code.</remarks>
protected virtual void MoveItemBase(int oldIndex, int newIndex) {
base.MoveItem(oldIndex, newIndex);
}
#endif
/// <summary>
/// Sets the item at the specified position.
/// </summary>
/// <param name = "index">The index to set the item at.</param>
/// <param name = "item">The item to set.</param>
protected override sealed void SetItem(int index, T item) {
Execute.OnUIThread(() => SetItemBase(index, item));
}
/// <summary>
/// Exposes the base implementation of the <see cref = "SetItem" /> function.
/// </summary>
/// <param name = "index">The index.</param>
/// <param name = "item">The item.</param>
/// <remarks>
/// Used to avoid compiler warning regarding unverifiable code.
/// </remarks>
protected virtual void SetItemBase(int index, T item) {
base.SetItem(index, item);
}
/// <summary>
/// Removes the item at the specified position.
/// </summary>
/// <param name = "index">The position used to identify the item to remove.</param>
protected override sealed void RemoveItem(int index) {
Execute.OnUIThread(() => RemoveItemBase(index));
}
/// <summary>
/// Exposes the base implementation of the <see cref = "RemoveItem" /> function.
/// </summary>
/// <param name = "index">The index.</param>
/// <remarks>
/// Used to avoid compiler warning regarding unverifiable code.
/// </remarks>
protected virtual void RemoveItemBase(int index) {
base.RemoveItem(index);
}
/// <summary>
/// Clears the items contained by the collection.
/// </summary>
protected override sealed void ClearItems() {
Execute.OnUIThread(ClearItemsBase);
}
/// <summary>
/// Exposes the base implementation of the <see cref = "ClearItems" /> function.
/// </summary>
/// <remarks>
/// Used to avoid compiler warning regarding unverifiable code.
/// </remarks>
protected virtual void ClearItemsBase() {
base.ClearItems();
}
/// <summary>
/// Raises the <see cref = "E:System.Collections.ObjectModel.ObservableCollection`1.CollectionChanged" /> event with the provided arguments.
/// </summary>
/// <param name = "e">Arguments of the event being raised.</param>
protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e) {
if (IsNotifying) {
base.OnCollectionChanged(e);
}
}
/// <summary>
/// Raises the PropertyChanged event with the provided arguments.
/// </summary>
/// <param name = "e">The event data to report in the event.</param>
protected override void OnPropertyChanged(PropertyChangedEventArgs e) {
if (IsNotifying) {
base.OnPropertyChanged(e);
}
}
/// <summary>
/// Adds the range.
/// </summary>
/// <param name = "items">The items.</param>
public virtual void AddRange(IEnumerable<T> items) {
Execute.OnUIThread(() => {
var previousNotificationSetting = IsNotifying;
IsNotifying = false;
var index = Count;
foreach(var item in items) {
InsertItemBase(index, item);
index++;
}
IsNotifying = previousNotificationSetting;
OnPropertyChanged(new PropertyChangedEventArgs("Count"));
OnPropertyChanged(new PropertyChangedEventArgs("Item[]"));
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
});
}
/// <summary>
/// Removes the range.
/// </summary>
/// <param name = "items">The items.</param>
public virtual void RemoveRange(IEnumerable<T> items) {
Execute.OnUIThread(() => {
var previousNotificationSetting = IsNotifying;
IsNotifying = false;
foreach(var item in items) {
var index = IndexOf(item);
if (index >= 0) {
RemoveItemBase(index);
}
}
IsNotifying = previousNotificationSetting;
OnPropertyChanged(new PropertyChangedEventArgs("Count"));
OnPropertyChanged(new PropertyChangedEventArgs("Item[]"));
OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
});
}
/// <summary>
/// Called when the object is deserialized.
/// </summary>
/// <param name="c">The streaming context.</param>
[OnDeserialized]
public void OnDeserialized(StreamingContext c) {
IsNotifying = true;
}
/// <summary>
/// Used to indicate whether or not the IsNotifying property is serialized to Xml.
/// </summary>
/// <returns>Whether or not to serialize the IsNotifying property. The default is false.</returns>
public virtual bool ShouldSerializeIsNotifying() {
return false;
}
}
PS。请记住，这个类使用Caliburn.Micro中的一些其他类，以便您可以通过自己复制/填充所有依赖项 - 或者 - 如果您没有使用任何其他应用程序框架 - 只需引用库二进制文件并给它机会。
我花了很多时间查看所有解决方案，但没有一个真正符合我的需要，直到我终于意识到问题：我不想要一个线程安全列表 - 我只是想要一个可以在任何线程上修改的非线程安全列表，但是通知UI线程的更改。
（不想要线程安全集合的原因是通常的 - 通常你需要执行多个操作，例如“如果它不在列表中，然后添加它”哪个线程安全列表实际上没有帮助，所以你想要控制自己锁定）。
该解决方案在概念上非常简单，并且对我来说效果很好。只需创建一个实现IList<T>和INotifyCollectionChanged的新列表类。将所需的所有调用委托给底层实现（例如List<T>），然后在需要的UI线程上调用通知。
public class AlbumList : IList<Album>, INotifyCollectionChanged
{
private readonly IList<Album> _listImplementation = new List<Album>();
public event NotifyCollectionChangedEventHandler CollectionChanged;
private void OnChanged(NotifyCollectionChangedEventArgs e)
{
Application.Current?.Dispatcher.Invoke(DispatcherPriority.Render,
new Action(() => CollectionChanged?.Invoke(this, e)));
}
public void Add(Album item)
{
_listImplementation.Add(item);
OnChanged(new NotifyCollectionChangedEventArgs(
NotifyCollectionChangedAction.Add, item));
}
public bool Remove(Album item)
{
int index = _listImplementation.IndexOf(item);
var removed = index >= 0;
if (removed)
{
_listImplementation.RemoveAt(index);
OnChanged(new NotifyCollectionChangedEventArgs(
NotifyCollectionChangedAction.Remove, item, index));
}
return removed;
}
// ...snip...
}
有一个详细的解释和实施here。它主要是为.NET 3.5 SP1编写的，但它仍然可以在4.0中运行。
此实现的主要目标是“真实”列表存在的时间长于其可绑定视图（例如，如果它绑定在用户可以打开和关闭的窗口中）。如果生命周期是另一种方式（例如，您从仅在窗口打开时运行的后台工作者更新列表），则可以使用一些更简单的设计。