c# - 从 Task.Run 获取返回值

Question

我有以下代码：

public static async Task<string> Start(IProgress<ProcessTaskAsyncExProgress> progress)
{
    const int total = 10;
    for (var i = 0; i <= total; i++)
    {
        await Task.Run(() => RunLongTask(i.ToString(CultureInfo.InvariantCulture)));
        if (progress != null)
        {
            var args = new ProcessTaskAsyncExProgress
            {
                ProgressPercentage = (int)(i / (double)total * 100.0),
                Text = "processing " + i
            };
            progress.Report(args);
        }
    }
    return "Done";
}

private static string RunLongTask(string taskName)
{
    Task.Delay(300);
    return taskName + "Completed!";
}

如何RunLongTask从这一行取回字符串值：await Task.Run(() => RunLongTask(i.ToString(CultureInfo.InvariantCulture)));？

我试过了：

var val = await Task.Run(() => RunLongTask(i.ToString(CultureInfo.InvariantCulture))).Result;

但是我收到一条错误消息，说“字符串不可等待”。

Answer 1

Result从末端删除。当您从 await-able 方法中await获得回报时。Result

var val = await Task.Run(() => RunLongTask(i.ToString(CultureInfo.InvariantCulture)));

Answer 2

这不是对旧问题的直接答案，但对于其他搜索：

“通常”您不应该这样做，但有时您需要匹配库 API，以便您可以使用如下包装函数：

private async Task<string> WrapSomeMethod(string someParam)
{
    //adding .ConfigureAwait(false) may NOT be what you want but google it.
    return await Task.Run(() => SomeObj.SomeMethodAsync(someParam)).ConfigureAwait(false);
}

然后用 .Result 调用它，如下所示：

string blah = WrapSomeMethod(someParam).Result;