便携式库中的定时器

Question

我在便携式库/ Windows Store中找不到计时器.(定位.net 4.5和Windows Store又称Metro)

有没有人知道如何创建某种计时事件？

我需要一些秒表,所以这应该每秒刷新一次

Answer 1

更新:我们已在Visual Studio 2013中修复此问题.针对Store(Windows 8.1)和.NET Framework 4.5.1项目的可移植库现在可以引用Timer.

这是我们的实施细节泄露给用户的不幸情况.当您只针对.NET 4.5和Windows应用商店应用时,我们实际上会让您构建针对不同的东西,然后定位到低级平台(.NET 4,SL 4/5,Phone 7.x).我们尝试将这两者视为相同,但在下面开始泄漏的有限变化(例如Timer和Reflection).我们在这里介绍其中一些内容:http://channel9.msdn.com/Shows/Going+Deep/NET-45-David-Kean-and-Marcea-Trofin-Portable-Libraries.

我们将在未来版本中考虑修复此问题.在那之前,您有几个解决方法:

1)使用Task.Delay实现自己的Timer版本,这是我们在内部使用的快速副本:

internal delegate void TimerCallback(object state);

internal sealed class Timer : CancellationTokenSource, IDisposable
{
    internal Timer(TimerCallback callback, object state, int dueTime, int period)
    {
        Contract.Assert(period == -1, "This stub implementation only supports dueTime.");
        Task.Delay(dueTime, Token).ContinueWith((t, s) =>
        {
            var tuple = (Tuple<TimerCallback, object>)s;
            tuple.Item1(tuple.Item2);
        }, Tuple.Create(callback, state), CancellationToken.None,
            TaskContinuationOptions.ExecuteSynchronously | TaskContinuationOptions.OnlyOnRanToCompletion,
            TaskScheduler.Default);
    }

    public new void Dispose() { base.Cancel(); }
}

2)将您的项目降级到.NET 4.0和Windows应用商店应用程序,这将使您可以访问Timer.

3)创建一个面向.NET 4.0和Windows应用商店应用的新项目,并将需要定时器的代码放入其中.然后从.NET 4.5和Windows应用商店应用项目中引用它.

作为旁注,我已经在PclContrib网站上为自己提交了一个工作项,以添加Timer支持:http://pclcontrib.codeplex.com/workitem/12513 .

Answer 2

根据David Kean的建议#3,这是我的hacky Timer适配器 - 将它放在一个针对.net 4.0的PCL库中,并从4.5引用它:

    public class PCLTimer
    {
        private Timer _timer;

        private Action _action;

        public PCLTimer(Action action, TimeSpan dueTime, TimeSpan period)
        {
            _action = action;

            _timer = new Timer(PCLTimerCallback, null, dueTime, period);           
        }

        private void PCLTimerCallback(object state)
        {
            _action.Invoke();
        }

        public bool Change(TimeSpan dueTime, TimeSpan period)
        {
            return _timer.Change(dueTime, period);
        }
    }

然后使用它,您可以从4.5 PCL库中执行此操作:

    private void TimeEvent()
    {            
        //place your timer callback code here
    }

    public void SetupTimer()
    {            
        //set up timer to run every second
        PCLTimer _pageTimer = new PCLTimer(new Action(TimeEvent), TimeSpan.FromMilliseconds(-1), TimeSpan.FromSeconds(1));

        //timer starts one second from now
        _pageTimer.Change(TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(1));

    }

Answer 3

执行David Kean提出的建议#1期间:

public delegate void TimerCallback(object state);

public sealed class Timer : CancellationTokenSource, IDisposable
{
    public Timer(TimerCallback callback, object state, int dueTime, int period)
    {
        Task.Delay(dueTime, Token).ContinueWith(async (t, s) =>
        {
            var tuple = (Tuple<TimerCallback, object>) s;

            while (true)
            {
                if (IsCancellationRequested)
                    break;
                Task.Run(() => tuple.Item1(tuple.Item2));
                await Task.Delay(period);
            }

        }, Tuple.Create(callback, state), CancellationToken.None,
            TaskContinuationOptions.ExecuteSynchronously | TaskContinuationOptions.OnlyOnRanToCompletion,
            TaskScheduler.Default);
    }

    public new void Dispose() { base.Cancel(); }
}