13

注意：如果您想要完整的源代码，此问题中的代码是deSleeper的一部分。

我想要的命令之一是异步操作的烘焙设计。我希望在命令执行时按下按钮禁用，并在完成后返回。我希望在 ThreadPool 工作项中执行实际工作。最后，我想要一种方法来处理异步处理期间发生的任何错误。

我的解决方案是 AsyncCommand：

public abstract class AsyncCommand : ICommand
{
    public event EventHandler CanExecuteChanged;
    public event EventHandler ExecutionStarting;
    public event EventHandler<AsyncCommandCompleteEventArgs> ExecutionComplete;

    public abstract string Text { get; }
    private bool _isExecuting;
    public bool IsExecuting
    {
        get { return _isExecuting; }
        private set
        {
            _isExecuting = value;
            if (CanExecuteChanged != null)
                CanExecuteChanged(this, EventArgs.Empty);
        }
    }

    protected abstract void OnExecute(object parameter);

    public void Execute(object parameter)
    {   
        try
        {
            IsExecuting = true;
            if (ExecutionStarting != null)
                ExecutionStarting(this, EventArgs.Empty);

            var dispatcher = Dispatcher.CurrentDispatcher;
            ThreadPool.QueueUserWorkItem(
                obj =>
                {
                    try
                    {
                        OnExecute(parameter);
                        if (ExecutionComplete != null)
                            dispatcher.Invoke(DispatcherPriority.Normal, 
                                ExecutionComplete, this, 
                                new AsyncCommandCompleteEventArgs(null));
                    }
                    catch (Exception ex)
                    {
                        if (ExecutionComplete != null)
                            dispatcher.Invoke(DispatcherPriority.Normal, 
                                ExecutionComplete, this, 
                                new AsyncCommandCompleteEventArgs(ex));
                    }
                    finally
                    {
                        dispatcher.Invoke(DispatcherPriority.Normal, 
                            new Action(() => IsExecuting = false));
                    }
                });
        }
        catch (Exception ex)
        {
            IsExecuting = false;
            if (ExecutionComplete != null)
                ExecutionComplete(this, new AsyncCommandCompleteEventArgs(ex));
        }
    }

    public virtual bool CanExecute(object parameter)
    {
        return !IsExecuting;
    }
}

所以问题是：这一切有必要吗？我注意到内置了对数据绑定的异步支持，那么为什么不执行命令呢？可能和参数问题有关，这是我的下一个问题。

4

2 回答 2

4

我已经能够细化原始样本，并为遇到类似情况的其他人提供一些建议。

首先，考虑 BackgroundWorker 是否能满足需求。我仍然经常使用 AsyncCommand 来获得自动禁用功能，但如果有很多事情可以用 BackgroundWorker 完成的话。

但是通过包装 BackgroundWorker，AsyncCommand 提供了具有异步行为的类似命令的功能（我也有关于这个主题的博客条目）

public abstract class AsyncCommand : ICommand
{
    public event EventHandler CanExecuteChanged;
    public event EventHandler RunWorkerStarting;
    public event RunWorkerCompletedEventHandler RunWorkerCompleted;

    public abstract string Text { get; }
    private bool _isExecuting;
    public bool IsExecuting
    {
        get { return _isExecuting; }
        private set
        {
            _isExecuting = value;
            if (CanExecuteChanged != null)
                CanExecuteChanged(this, EventArgs.Empty);
        }
    }

    protected abstract void OnExecute(object parameter);

    public void Execute(object parameter)
    {   
        try
        {   
            onRunWorkerStarting();

            var worker = new BackgroundWorker();
            worker.DoWork += ((sender, e) => OnExecute(e.Argument));
            worker.RunWorkerCompleted += ((sender, e) => onRunWorkerCompleted(e));
            worker.RunWorkerAsync(parameter);
        }
        catch (Exception ex)
        {
            onRunWorkerCompleted(new RunWorkerCompletedEventArgs(null, ex, true));
        }
    }

    private void onRunWorkerStarting()
    {
        IsExecuting = true;
        if (RunWorkerStarting != null)
            RunWorkerStarting(this, EventArgs.Empty);
    }

    private void onRunWorkerCompleted(RunWorkerCompletedEventArgs e)
    {
        IsExecuting = false;
        if (RunWorkerCompleted != null)
            RunWorkerCompleted(this, e);
    }

    public virtual bool CanExecute(object parameter)
    {
        return !IsExecuting;
    }
}
于 2008-10-23T06:22:02.527 回答
1

正如我在您的另一个问题中回答的那样，您可能仍希望同步绑定到此，然后异步启动命令。这样你就避免了你现在遇到的问题。

于 2008-09-30T04:18:22.277 回答