WPF ObservableCollection线程安全 [英] WPF ObservableCollection Thread Safety

问题描述

我有一个MVVM设置.

I've got a MVVM setup.

我的模型定期调用一些服务，然后在ViewModel上调用一个操作，然后更新暴露给View的一些变量.

My model periodically calls some service and then invokes an action on the ViewModel which then updates some variables exposed to the View.

该变量是一个ReadOnlyObservableCollection<T>，它具有一个要侦听的ObservableCollection<T>.

The variable is an ReadOnlyObservableCollection<T>, which has an ObservableCollection<T> it listens on.

问题在于模型从另一个线程调用回调，因此不允许我在另一个线程上清除ObservableCollection<T>.

The problem is that the Model calls the callback from a different thread, and thus it doesn't allow me to clear the ObservableCollection<T> on a different thread.

所以我想:使用调度程序，如果我们不在正确的线程上，请调用它:

So I thought: use the dispatcher, if we aren't on the correct thread, invoke it:

    private void OnNewItems(IEnumerable<Slot> newItems)
    {
        if(!Dispatcher.CurrentDispatcher.CheckAccess())
        {
            Dispatcher.CurrentDispatcher.Invoke(new Action(() => this.OnNewItems(newItems)));
            return;
        }

        this._internalQueue.Clear();
        foreach (Slot newItem in newItems)
        {
            this._internalQueue.Add(newItem);
        }
    }

我认为代码非常简单

问题是，即使我在正确的线程上执行它(我认为)，它仍会在.Clear();

The problem is that, even though I execute it on the correct thread (I think) it still throws me an exception on the .Clear();

为什么会这样?如何在不创建自定义ObservableCollection<T>的情况下解决该问题?

Why is this occuring? How can I work around it without creating my custom ObservableCollection<T>?

推荐答案

我通常会在通用视图模型库中初始化我的视图模型使用的调度程序，以帮助确保它是UI线程调度程序，如Will所述.

I typically initialize the dispatcher used by my view models in a common view model base to help ensure it is the UI thread dispatcher, as Will mentions.

#region ViewModelBase()
/// <summary>
/// Initializes a new instance of the <see cref="ViewModelBase"/> class.
/// </summary>
protected ViewModelBase()
{
    _dispatcher = Dispatcher.CurrentDispatcher;
}
#endregion

#region Dispatcher
/// <summary>
/// Gets the dispatcher used by this view model to execute actions on the thread it is associated with.
/// </summary>
/// <value>
/// The <see cref="System.Windows.Threading.Dispatcher"/> used by this view model to 
/// execute actions on the thread it is associated with. 
/// The default value is the <see cref="System.Windows.Threading.Dispatcher.CurrentDispatcher"/>.
/// </value>
protected Dispatcher Dispatcher
{
    get
    {
        return _dispatcher;
    }
}
private readonly Dispatcher _dispatcher;
#endregion

#region Execute(Action action)
/// <summary>
/// Executes the specified <paramref name="action"/> synchronously on the thread 
/// the <see cref="ViewModelBase"/> is associated with.
/// </summary>
/// <param name="action">The <see cref="Action"/> to execute.</param>
protected void Execute(Action action)
{
    if (this.Dispatcher.CheckAccess())
    {
        action.Invoke();
    }
    else
    {
        this.Dispatcher.Invoke(DispatcherPriority.DataBind, action);
    }
}
#endregion

然后您可以像这样在视图模型调度程序上调用一个动作:

You could then invoke an action on the view model dispatcher like this:

this.Execute(
    () =>
    {
        this.OnNewItems(newItems);
    }
);

这篇关于WPF ObservableCollection线程安全的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！