How to save the state of views held in dynamic viewpager

Question

I have an enhanced loop, which will dynamically inflate however many layouts relevant to the number of values held in my array.

This works perfectly however, there is a method being called on each iteration, which also works but there is a big bug that I need help resolving.

Imagine there are 5 items in my array, therefore 5 layouts are inflated, in these layouts there is a little scratchcard type section on the layout.

Now if the user is on page 1, uses the scratchcard, then moves on to page 2, uses the scratchcard etc etc, it works fine.

But if the user is on page 1 and then goes to say, page 5 and then back to page 1 (basically in a random order), the scratchcard doesn't work.

From my understanding, the reason for this is that the method is being called an implemented on each iteration and the view is losing its state if the user scrolls back or scrolls in random orders.

Therefore I need a way to save the created view state in my viewpager.

Is this possible for my scenario? I have tried my best to find a solution, but cannot find something that feels relevant to my question.

Here is a snippet of the code in question. Thanks for any guidance or suggestions!

for (String x : array1) {
                //loop out the number of layouts relative to the number of questions held in x
                View current_layout = LayoutInflater.from(getActivity()).inflate(R.layout.question_fragment, null);
                //use the pageAdapter to add the layout to the users view
                pagerAdapter.addView(current_layout);

                //call method to add functionality to the scratchcard
                isCorrect(current_layout);
}



public void isCorrect(View current_layout) {



        ScratchoffController controller1 = new ScratchoffController(getActivity())
                .setThresholdPercent(0.40d)
                .setTouchRadiusDip(getActivity(), 30)
                .setFadeOnClear(true)
                .setClearOnThresholdReached(true)
                .setCompletionCallback(() -> {
                })
                .attach(current_layout.findViewById(R.id.scratch_view1), current_layout.findViewById(R.id.scratch_view_behind1));



        ScratchoffController controller2 = new ScratchoffController(getActivity())
                .setThresholdPercent(0.40d)
                .setTouchRadiusDip(getActivity(), 30)
                .setFadeOnClear(true)
                .setClearOnThresholdReached(true)
                .setCompletionCallback(() -> {
                })
                .attach(current_layout.findViewById(R.id.scratch_view2), current_layout.findViewById(R.id.scratch_view_behind2));

        ScratchoffController controller3 = new ScratchoffController(getActivity())
                .setThresholdPercent(0.40d)
                .setTouchRadiusDip(getActivity(), 30)
                .setFadeOnClear(true)
                .setClearOnThresholdReached(true)
                .setCompletionCallback(() -> {
                })
                .attach(current_layout.findViewById(R.id.scratch_view3), current_layout.findViewById(R.id.scratch_view_behind3));

        ScratchoffController controller4 = new ScratchoffController(getActivity())
                .setThresholdPercent(0.40d)
                .setTouchRadiusDip(getActivity(), 30)
                .setFadeOnClear(true)
                .setClearOnThresholdReached(true)
                .setCompletionCallback(() -> {
                })
                .attach(current_layout.findViewById(R.id.scratch_view4), current_layout.findViewById(R.id.scratch_view_behind4));



    }

Answer 1

I ussually use ViewPager with Fragments and what you mention has happend to me when I try to keep references to the Fragment instances (in my case) outside of the viewpager.

This happens because the viewpager may create new instances of the Fragment it contains when you re-vist the tab in the way you mention. When this happens, the instance reference you hold outside of the viewpager is not anymore what the viewpager is showing.

In your case , according to this question, you have to oveeride instatiateItem and destroyItem. I think you can use these methods to save state restore state, and also you could update any external reference when instantiateItem is called.