Concurrently awaiting multiple asynchronous calls with independent continuations

Question

There are several scenarios where I need to invoke multiple asynchronous calls (from the same event handler) that can proceed independently of each other, with each one havi

Answer 1

The traditional approach was to use ContinueWith for registering the respective continuation to each asynchronous task:

private async void button_Click(object sender, RoutedEventArgs e)
{
    TaskScheduler uiScheduler = TaskScheduler.FromCurrentSynchronizationContext();
    await Task.WhenAll(
        GetNameAsync().ContinueWith(nameTask => { nameTextBox.Text = nameTask.Result; }, uiScheduler),
        GetCityAsync().ContinueWith(cityTask => { cityTextBox.Text = cityTask.Result; }, uiScheduler),
        GetRankAsync().ContinueWith(rankTask => { rankTextBox.Text = rankTask.Result; }, uiScheduler));
}

With C# 5, it is now preferable to use an await-style pattern. This may be most easily achieved by splitting up each task–continuation pair into its own method:

private async void button_Click(object sender, RoutedEventArgs e)
{
    await Task.WhenAll(
        PopulateNameAsync(),
        PopulateCityAsync(),
        PopulateRankAsync());
}

private async Task PopulateNameAsync()
{
    nameTextBox.Text = await GetNameAsync();
}

private async Task PopulateCityAsync()
{
    cityTextBox.Text = await GetCityAsync();
}

private async Task PopulateRankAsync()
{
    rankTextBox.Text = await GetRankAsync();
}

Defining all these trivial methods quickly become cumbersome, so one may condense them into async lambdas instead:

private async void button_Click(object sender, RoutedEventArgs e)
{
    await Task.WhenAll(
        new Func(async () => { nameTextBox.Text = await GetNameAsync(); })(),
        new Func(async () => { cityTextBox.Text = await GetCityAsync(); })(),
        new Func(async () => { rankTextBox.Text = await GetRankAsync(); })());
}

If this pattern is used frequently, it would also be helpful to define a utility method that can take the Func lambdas and execute them, making our event handler's code more concise and readable:

public static Task WhenAllTasks(params Func[] taskProducers)
{
    return Task.WhenAll(taskProducers.Select(taskProducer => taskProducer()));
}

private async void button_Click(object sender, RoutedEventArgs e)
{
    await WhenAllTasks(
        async () => nameTextBox.Text = await GetNameAsync(),
        async () => cityTextBox.Text = await GetCityAsync(),
        async () => rankTextBox.Text = await GetRankAsync());
}