中继命令可以执行和任务 [英] Relay Command can execute and a Task

问题描述

我想在调用中继命令时启动任务，但是只要该任务正在运行，我想禁用该按钮

i want to start a task when a relay command is called, however i want to disable the button as long as that task is running

举个例子

private ICommand update;
public ICommand Update
        {
            get
            {
                if (update == null)
                {
                    update = new RelayCommand(
                        param => Task.Factory.StartNew(()=> StartUpdate()),
                        param => true); //true means the button will always be enabled
                }
                return update;
            }
        }

检查该任务是否正在运行的最佳方法是什么?

what is the best way to check if that task is running?

这是我的解决方案，但不确定它是否是最好的方法

here is my solution but not sure if its the best way

class Vm : ObservableObject 
    {

        Task T;
        public Vm()
        {
            T = new Task(() => doStuff());
        }

        private ICommand myCommand;
        public ICommand MyCommand
        {
            get { return myCommand ?? (myCommand = new RelayCommand( p => { T = new Task(() => doStuff()); T.Start(); }, p => T.Status != TaskStatus.Running)); }
        }


        private void doStuff()
        {
            System.Threading.Thread.Sleep(5000);
        }

    }

更新:这里的每个答案都很好，但他们仍然不同意对方，我刚刚达到了 100 声望，每当我达到 100 时我就会开始赏金，所以我正在寻找的是一个实现在 .net 4.0 中的任务中执行的最佳非内存泄漏异步 RelayCommand

推荐答案

我认为，你可以使用 AsyncCommand 的这个实现.

I think, you can use this implementation of AsyncCommand.

public class AsyncCommand : ICommand, IDisposable
{
    private readonly BackgroundWorker _backgroundWorker = new BackgroundWorker {WorkerSupportsCancellation = true};
    private readonly Func<bool> _canExecute;

    public AsyncCommand(Action action, Func<bool> canExecute = null, Action<object> completed = null,
                        Action<Exception> error = null)
    {
        _backgroundWorker.DoWork += (s, e) =>
            {
                CommandManager.InvalidateRequerySuggested();
                action();
            };

        _backgroundWorker.RunWorkerCompleted += (s, e) =>
            {
                if (completed != null && e.Error == null)
                    completed(e.Result);

                if (error != null && e.Error != null)
                    error(e.Error);

                CommandManager.InvalidateRequerySuggested();
            };

        _canExecute = canExecute;
    }

    public void Cancel()
    {
        if (_backgroundWorker.IsBusy)
            _backgroundWorker.CancelAsync();
    }

    public bool CanExecute(object parameter)
    {
        return _canExecute == null
                   ? !_backgroundWorker.IsBusy
                   : !_backgroundWorker.IsBusy && _canExecute();
    }

    public void Execute(object parameter)
    {
        _backgroundWorker.RunWorkerAsync();
    }

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        if (disposing)
        {
            if (_backgroundWorker != null)
                _backgroundWorker.Dispose();
        }
    }
}

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