令我惊讶的是，Profile 78 库中不存在方便的 System.Threading.Timer 类。为了使用这个类，我创建了另一个以 4.0 框架为目标的 PCL，并编写了一个简单的包装器(正如一篇博文中所建议的那样):

public class PCLTimer
{
    private Timer timer;
    private Action<object> action;

    public PCLTimer (Action<object> action, object state, int dueTimeMilliseconds, int periodMilliseconds)
    {
        this.action = action;
        timer = new Timer (PCLTimerCallback, state, dueTimeMilliseconds, periodMilliseconds);
    }

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

    public bool Change (int dueTimeMilliseconds, int periodMilliseconds)
    {
        return timer.Change (dueTimeMilliseconds, periodMilliseconds);
    }
}

现在我可以引用这个 4.0 库并在主 PCL 库中使用 PCLTimer。但是当我尝试构建我的主要 Android 项目时，我收到以下警告:

Warning CS1684: Reference to type 'System.Threading.Timer' claims it is defined in 'c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETPortable\v4.5\Profile\Profile78\mscorlib.dll', but it could not be found (CS1684) (Prototype.Core)

Warning MSB3247: Found conflicts between different versions of the same dependent assembly. (MSB3247) (Prototype.Droid)

如何正确去除这些警告？

最佳答案

这是使用异步任务对 Profile 78 中暂时消失的 Timer 类的完整重新实现:

using System;
using System.Threading;
using System.Threading.Tasks;

namespace Quantum
{
    public delegate void TimerCallback(object state);

    public sealed class Timer : IDisposable
    {
        private static Task CompletedTask = Task.FromResult(false);

        private TimerCallback Callback;
        private Task Delay;
        private bool Disposed;
        private int Period;
        private object State;
        private CancellationTokenSource TokenSource;

        public Timer(TimerCallback callback, object state, int dueTime, int period)
        {
            Callback = callback;
            State = state;
            Period = period;
            Reset(dueTime);
        }

        public Timer(TimerCallback callback, object state, TimeSpan dueTime, TimeSpan period)
            : this(callback, state, (int)dueTime.TotalMilliseconds, (int)period.TotalMilliseconds)
        {
        }

        ~Timer()
        {
            Dispose(false);
        }

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

        private void Dispose(bool cleanUpManagedObjects)
        {
            if (cleanUpManagedObjects)
                Cancel();
            Disposed = true;
        }

        public void Change(int dueTime, int period)
        {
            Period = period;
            Reset(dueTime);
        }

        public void Change(TimeSpan dueTime, TimeSpan period)
        {
            Change((int)dueTime.TotalMilliseconds, (int)period.TotalMilliseconds);
        }

        private void Reset(int due)
        {
            Cancel();
            if (due >= 0)
            {
                TokenSource = new CancellationTokenSource();
                Action tick = null;
                tick = () =>
                {
                    Task.Run(() => Callback(State));
                    if (!Disposed && Period >= 0)
                    {
                        if (Period > 0)
                            Delay = Task.Delay(Period, TokenSource.Token);
                        else
                            Delay = CompletedTask;
                        Delay.ContinueWith(t => tick(), TokenSource.Token);
                    }
                };
                if (due > 0)
                    Delay = Task.Delay(due, TokenSource.Token);
                else
                    Delay = CompletedTask;
                Delay.ContinueWith(t => tick(), TokenSource.Token);
            }
        }

        private void Cancel()
        {
            if (TokenSource != null)
            {
                TokenSource.Cancel();
                TokenSource.Dispose();
                TokenSource = null;
            }
        }
    }
}

关于c# - PCL 配置文件 78 中的 System.Threading.Timer 问题 - 警告，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22619896/