How to check that all files are uploaded (using Picasso)?

Question

Java

I want to check that all files are loaded before rendering the MainActivity:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ...
    getBitmapsByURLs(urls);
    // здесь бы знать, что да, всё уже загружено, вот список Bitmap'ов. 
}

public void getBitmapsByURLs(List<String> urls) {
    final List<Target> targets = new ArrayList<>();

    for (int i = 0; i < urls.size(); i++) {
        final int k = i;
        Target target = new Target() {

            @Override
            public void onBitmapLoaded(Bitmap bitmap, Picasso.LoadedFrom from) {
                Log.i("TEMP", "Loaded: " + k);
                targets.remove(this);
            }

            @Override
            public void onBitmapFailed(Drawable errorDrawable) {
                targets.remove(this);
            }

            @Override
            public void onPrepareLoad(Drawable placeHolderDrawable) {
                Log.i("TEMP", "Preparing: " + k);
            }
        };
        targets.add(target);
        Picasso.with(this)
                .load(urls.get(i))
                .memoryPolicy(NO_CACHE, NO_STORE)
                .into(target);
    }
}

How can I check? If I add to onCreate (after getBitmapsByURLs) whilethen it will be infinite because it will run before all the images have loaded. Please tell me how to do it right? I'm still learning.