Activity Indicator is not visible on xaml page in xamarin.forms? - xamarin.forms

Question

I have an activity indicator on xaml page. Initially its IsVisible property is false. I have a button on page. When user click on button it calls a web service to get data. I change the value of IsVisible property to true before calling the service so that activity indicator starts to display on page and after successful calling of service I change its value to again false so that it doesn't show any more on page.
But it is not working. I know the actual problem. When we call the web service the UI thread gets block and it doesn't show the activity indicator.
How I can enable the UI thread when web service gets called so that activity indicator can show on page until we get the data?

Answer 1

Try making your webservice call into an async and await it.
Depending on how you've structured things you may have to use a TaskCompletionSource as the following example demonstrates.
In this example when the button is clicked, the button is made invisible, and the ActivityIndicator is set to IsRunning=True to show it.
It then executes your long running task / webservice in the function ExecuteSomeLongTask using a TaskCompletionSource.
The reason for this is that in our button click code, we have the final lines:-
objActivityIndicator1.IsRunning = false;
objButton1.IsVisible = true;
That stop the ActivityIndicator from running and showing, and also set the button back to a visible state.
If we did not use a TaskCompletionSource these lines would execute immediately after calling the ExecuteSomeLongTask if it was a normal async method / function, and would result in the ActivityIndicator not running and the button still being visible.
Example:-
Grid objGrid = new Grid()
{
};
ActivityIndicator objActivityIndicator1 = new ActivityIndicator();
objGrid.Children.Add(objActivityIndicator1);
Button objButton1 = new Button();
objButton1.Text = "Execute webservice call.";
objButton1.Clicked += (async (o2, e2) =>
{
objButton1.IsVisible = false;
objActivityIndicator1.IsRunning = true;
//
bool blnResult = await ExecuteSomeLongTask();
//
objActivityIndicator1.IsRunning = false;
objButton1.IsVisible = true;
});
objGrid.Children.Add(objButton1);
return objGrid;
Supporting function:-
private Task<bool> ExecuteSomeLongTask()
{
TaskCompletionSource<bool> objTaskCompletionSource1 = new TaskCompletionSource<bool>();
//
Xamarin.Forms.Device.StartTimer(new TimeSpan(0, 0, 5), new Func<bool>(() =>
{
objTaskCompletionSource1.SetResult(true);
//
return false;
}));
//
return objTaskCompletionSource1.Task;
}

Answer 2

You need to do your work in an asynchronous way. Or in other words: Use Asnyc & Await to ensure, that you UI works well during the call.
You can find more informations in the Xamarin Docs.
async and await are new C# language features that work in conjunction
with the Task Parallel Library to make it easy to write threaded code
to perform long-running tasks without blocking the main thread of your
application.
If you need further asistance, please update your question and post your code or what you have tried so far.