连接到Web服务器时的Xamarin进度指示器

Question

I'm facing a problem with Async operation when App starts.

During OnCreate , I start a background operation that call a web service to test if the service is available. In the activity, I have a label with Connecting... text. When the async operation completes, the label's text is changed to OK or No service .

Now the question is: can I show to my user that an async operation is in progress?

I cannot figure out how I can use another async operation can show some animation while the server responds and complete the second async operation when the first completes.

Answer 1

You would ideally create a custom View which renders the animation (or use the SDK built-in indeterminate ProgressBar ) and place it in your layout, with its visibility set to ViewStates.Gone .

Before the async operation is launched, the view's visibility is set to ViewStates.Visible , and after the async operation completes, the visibility is again set to Gone . You may even remove the view from the layout if you want after the async operation completes.

You'd have something like (pseudo-C#)

async void OnCreate()
{
    // Some code (get references to views, etc.)

    progressView.Visibility = ViewStates.Visible;

    var asyncResult = await SomeAsyncOperation();

    progressView.Visibility = ViewStates.Gone;

    // Some more code
}