将异步编程模型（开始/结束方法）转换为基于事件的异步模型？

Question

假设我有使用异步编程模型的代码，即它提供以下方法作为可以同步或异步使用的组：

public MethodResult Operation(<method params>);

public IAsyncResult BeginOperation(<method params>, AsyncCallback callback, object state);
public MethodResult EndOperation(IAsyncResult ar);

我想要做的是将这个代码包装一个额外的层，将其转换为事件驱动的异步模型，如下所示：

public void OperationAsync(<method params>);
public event OperationCompletedEventHandler OperationCompleted;
public delegate void OperationCompletedEventHandler(object sender, OperationCompletedEventArgs e);

有没有人对如何做到这一点有任何指导（或链接到这样的指导）？

Answer 1

有关这方面的一些想法，请参阅"Async without the pain";提供的代码使用回调方法，但如果将其放在实例上，事件就很容易了。

public static void RunAsync<T>(
    Func<AsyncCallback, object, IAsyncResult> begin,
    Func<IAsyncResult, T> end,
    Action<Func<T>> callback) {
    begin(ar => {
        T result;
        try {
            result = end(ar); // ensure end called
            callback(() => result);
        } catch (Exception ex) {
            callback(() => { throw ex; });
        }
    }, null);
}

Answer 2

您可以使用AsyncFunc库进行包装。

http://asyncfunc.codeplex.com

代码如下所示：

public class Original
{
    public ResultType Operation(ParamType param){...}
    public IAsyncResult BeginOperation(ParamType param, AsyncCallback callback, object state){...}
    public ResultType EndOperation(IAsyncResult ar){...}
}

public class Wrapper
{
    private AsyncFunc<ParamType, ResultType> _operation;
    private Original _original;

    public Wrapper(Original original)
    {
        _original = original;
        _operation = AsyncFunc<ParamType, ResultType>(_original.Operation);
    }

    public ResultType Operation(ParamType param)
    {
        return _original.Operation(param);
    }

    public void OperationAsync(ParamType param)
    {
        _operation.InvokeAsync(param)
    }

    public event AsyncFuncCompletedEventHandler<ResultType> OperationCompleted      
      {
        add { _operation.Completed += value; }
        remove { _operation.Completed -= value; }
    }
}

请注意，在此方法中，您不需要定义自定义事件参数类和事件处理程序委托。它们可以用AsyncFunc泛型类型代替：

OperationCompletedEventArgs -> ResultType
OperationCompletedEventHandler -> AsyncFuncCompletedEventHandler<ResultType>

有关更高级的方案，请转到AsyncFunc主页。有一些视频和样本。