将事件转换为异步调用

Question

我正在包装一个供我自己使用的库.要获得某个属性,我需要等待一个事件.我正在尝试将其包装成异步调用.

基本上,我想转

void Prepare()
{
    foo = new Foo();
    foo.Initialized += OnFooInit;
    foo.Start();
}
string Bar
{
    return foo.Bar;  // Only available after OnFooInit has been called.
}

进入这个

async string GetBarAsync()
{
    foo = new Foo();
    foo.Initialized += OnFooInit;
    foo.Start();
    // Wait for OnFooInit to be called and run, but don't know how
    return foo.Bar;
}

怎么能最好地完成？我可以循环并等待,但我正在尝试找到更好的方法,如使用Monitor.Pulse(),AutoResetEvent或其他东西.

Answer 1

这就是TaskCompletionSource发挥作用的地方.这里新的async关键字几乎没有空间.例:

Task<string> GetBarAsync()
{
    TaskCompletionSource<string> resultCompletionSource = new TaskCompletionSource<string>();

    foo = new Foo();
    foo.Initialized += OnFooInit;
    foo.Initialized += delegate
    {
        resultCompletionSource.SetResult(foo.Bar);
    };
    foo.Start();

    return resultCompletionSource.Task;
}

样本使用(花式异步)

async void PrintBar()
{
    // we can use await here since bar returns a Task of string
    string bar = await GetBarAsync();

    Console.WriteLine(bar);
}