c# - Metro C# 中的虚拟异步方法

Question

我想定义一个虚方法，它在基类中不是异步的，但在派生类中是异步的，调用者使用委托(delegate)调用它(实际上它是一个由屏幕上的按钮激活的 ICommand)我怎么能这样做。

public class BaseClass
{
    BIONESSBindingCommand mLogoffCommand;

    public ICommand LogoffCommand
    {
        get
        {
            if (mLogoffCommand == null)
            {
                mLogoffCommand = new BIONESSBindingCommand(
                    Param => Logoff(), //Command DoWork
                    Param => true); //Always can execute
            }

            return mLogoffCommand;
        }
    }

    public virtual Task Logoff()
    {
        DoLogoff();
        return null; //???
    }
}

public class DerivedClass : BaseClass
{
    public override async Task Logoff()
    {
        await SomeWoAsyncWork();
        base.Logoff(); //Has warninngs
    }
}

Answer 1

调用Task.FromResult 来获得一个完成的Task。此外，在派生类中await它(这将启用错误传播)。

public class BaseClass
{
  public virtual Task Logoff()
  {
    DoLogoff();
    return Task.FromResult(false);
  }
}

public class DerivedClass : BaseClass
{
  public override async Task Logoff()
  {
    await SomeWoAsyncWork();
    await base.Logoff();
  }
}