了解基于任务的异步模式C＃

Question

I am starting to study C# TAP coding. I don't understand why the code is running synchronously

    async private void timer1_Tick(object sender, EventArgs e)
    {
        SyncCount++;
        result1.Text = SyncCount.ToString();

        AsyncCount = await CountForALongTimeAsync(AsyncCount);
        result2.Text = AsyncCount.ToString();
    }

    async Task<int> CountForALongTimeAsync(int counter)
    {
        Thread.Sleep(3000);
        counter++;
        return counter;
    }

Answer 1

async Task<int> CountForALongTimeAsync(int counter)
{

What comes next will be executed until the first await ed async call that actually does some waiting (it's possible that a given call could have all it needs to return immediately, eg a service that might hit the internet or might return data from a cache, in which case it won't wait).

There are no await ed calls at all, so the Task returned is returned already completed.

Since the calling await CountForALongTimeAsync is await ing a task that is returned already completed, it runs synchronously.

The method would be better as:

async Task<int> CountForALongTimeAsync(int counter)
{
    await Task.Delay(3000);
    counter++;
    return counter;
}

Incidentally, the pre await way of doing something very (but not entirely) similar would have been:

Task<int> CountForALongTimeAsync(int counter)
{
    return Task.Delay(3000).ContinueWith(t =>
    {
        ++counter;
        return counter;
    });
}

Considering that these are different ideas of "continuing" after a task might or might not give some insight.

In contrast the closest pre-await way of doing what the code in your question does was:

Task<int> CountForALongTimeAsync(int counter)
{
    Thread.Sleep(3000);
    counter++;
    return Task.FromResult(counter); //FromResult returns an already completed task.
}