xamarin forms update UI with await/async

Question

I am writting a very basic Xamarin Forms Application, with Visual Studio for Mac. This application should work with PCL on Android and iOS.

I have an empty TableView on XAML file. What i want to do is to populate this TableView with data i will fetch from a webservice.

Here is my C# code:

HttpClient client = new HttpClient();

public async Task<List<MyItem>> LoadData()
{
    try
    {
        var response = await client.GetAsync(new Uri("http://example.com/myservice.php"));
        if (response.IsSuccessStatusCode)
        {
            var content = await response.Content.ReadAsStringAsync();
            return JsonConvert.DeserializeObject<List<MyItem>>(content);
        }
    }
    catch (Exception)
    {
        return null;
    }

    return null;
}

async void Handle_Clicked(object sender, System.EventArgs e)
{
    activity_indicator.IsRunning = true;
    var data = await LoadData();
    activity_indicator.IsRunning = false;

    mylistview.Root.Clear();
    foreach (var item in data)
    {
        TableSection section = new TableSection() { Title = item.GroupTitle };
        foreach (var subitem in item.subitems)
        {
            var cell = new TextCell() { Text = subitem.Title };
            cell.Tapped += on_item_tapped;
            section.Add(cell);
        }
        mylistview.Root.Add(section);
    }
}

I am new to await and async programming. I used to develop native iOS application with iOS delegates. I have heard that a thread cannot update UI: Can i made some UI updates in LoadData() method for example ? So i am wondering if my code is good. It looks fine because it works, but i want to know if this is a good thing to work like this ?

Using async/await here is the correct choice. await on the UI thread will capture the current context and resume on that context when the asynchronous call completes which makes updating the ui after the call finishes trivial as you can see. One suggestions I'd make is to factor out the code in Handle_Clicked into an item template but that has nothing to do with async. — JSteward
Do you think the UI is reactive when the main thread is waiting on an await instruction ? — Bob5421

jharr100 jharr100 · Accepted Answer · 2017-06-19T20:01:34

5

votes

I believe its

Device.BeginInvokeOnMainThread(() =>
{

});

xamarin forms update UI with await/async

2 Answers