Display a progress bar during Activity's OnCreate()?

Question

EDIT 1:

This is the code that I have right now, trying to offload the heavy work on a separate thread.

protected override void OnCreate(Android.OS.Bundle bundle)
{
    // Set our view from the "main" layout resource
    SetContentView(Resource.Layout.Main);
}
protected override void OnResume()
{
   base.OnResume();

ThreadPool.QueueUserWorkItem(_ => BuildInterfaceForConnectedUser());
}

private void BuildInterfaceForConnectedUser()
{
    RunOnUiThread(() => { UpdateInterface();});
}

---

The ability to display a progress bar while background work is in progress has been asked many times, like here or here.

My problem is that I'm building my main activity content dynamically based on incoming data. I'm downloading data during a splash activity so this is easy to run it as a background task (because no UI access in involved). On the other end, building the content could take several seconds and I'd like to inform the user of the progress.

Basically, there is a lot of work in OnResume(). Pseudo code:

protected override void OnResume()
{
     base.OnResume();

     UpdateInterface(); // Build the content dynamically
}

During all this time the main activity is not showing.

How can I make the main activity to be displayed blurred in the background with a progress bar while the final content is built ?

It is started like the following from a "Login" Activity:

Intent intent = new Intent(this, typeof(MainActivity));
if(Intent.Extras != null) intent.PutExtras(Intent.Extras);
StartActivity(intent);

All the samples I've seen so far are not working because they rely on a button click where the activity is already built.

Answer 1

Basically, there is a lot of work in OnResume().

There should not be a lot of work in onResume(). Start this work on a seperate thread and then inform the UI thread about the results.

In Java/Kotlin this could be easily done with AsyncTask or you could use a traditional Thread+ Handler's.

Edit:

An equivalent approach using Java and AsyncTask.

public class Activity extends Activity{ 
 public void onCreate(){
   super(/*...*/);
   setContentView(splash_layout_id);
 }

 public void onResume(){
   super(/*...*/);
   task.execute();
 }

private AsynkTask task = new AsynkTask(){

   void doInBackground(){
     // this runs in the background
     Object data;

     while(data = fetchingData() != null){
      // this calls onProgressUpdate()
      publishProgress(data);
     }
   }

   void onProgressUpdate(Object progress) {
     // this runs on UI thread    
     updateUiRelativeToProgress(progress);
   }

   void onPostExecute(Object data) {
     // this runs on UI thread and called when doInBackground() returns 
     updateUi(data);
   }
 };

} 

Answer 2

How I usually do this is quite simple actually.

Since ProgressDialog is deprecated in API- 26, I tend to use ProgressBar to do this instead

1. Define a Global field as follows:

   ProgressBar progressBar;
   

2. Add a ProgressBar to your View via code into the TopMost layout which should always be a RelativeLayout, Something like the following :

     RelativeLayout layout = *Assignment*; // Assign your main relative layout here.
     RelativeLayout.LayoutParams relativeParams = new RelativeLayout.LayoutParams(100, 100);
     relativeParams.AddRule(LayoutRules.CenterInParent);
     progressbar= GetProgressBar(this)
     layout.addView(progressbar,params);
   

   Where GetProgressBar is a generic static method something like this:

     public static ProgressBar GetProgressBar(Activity _activity)
       {
           var progressBar = new ProgressBar(_activity, null, Android.Resource.Attribute.ProgressBarStyleLarge);              
           progressBar.Visibility=ViewStates.Visible;  //To show ProgressBar
           progressBar.Visibility=ViewStates.Gone;     // To Hide ProgressBar
           return progressBar;
       }
   

3. Then Once you have done this disable the entire view using this:

   Window.SetFlags(WindowManagerFlags.NotTouchable, WindowManagerFlags.NotTouchable);
   

4. Create an async Task that you want to run when your UpdateInterface method is called;

   private async void DoATask()
   {
      progressBar.Visibility=ViewStates.Visible; 
      await UpdateInterface();
      progressBar.Visibility=ViewStates.Gone; 
   }
   

   Note: UpdateInterface() method should be a System.Threading.Tasks.Task and not a Void for this to work because void cannot have a definition for awaiter to it.

5. In your OnResume or OnCreateRun this in UIThread

    protected override void OnResume()
    {
       base.OnResume();
        _activity.RunOnUiThread(DoATask);
    }
   

Hope this helps and works fine for you revert in case of queries