异步WPF命令

Question

注意:如果您需要完整的源代码,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.我希望在执行命令时按下按钮以禁用,并在完成时返回.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过程中发生的任何错误.

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:这一切都是必要的吗？我注意到内置异步支持数据绑定,为什么不执行命令呢？也许它与参数问题有关,这是我的下一个问题.

Answer 1

我已经能够改进原始示例，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，但如果很多事情可以用BackgroundWorker完成。

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（我还有一篇关于此主题的博客文章）

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;
    }
}