Using BillingDataSource.java of Android example

Question

I am trying to use

BillingDataSource.java
Security.java

from TrivialDriveSample I managed to get the purchase for a Premium SKU (one time purchase) but where can I check if this product is bought when my App start in order to unlock features each time the App starts I need to call from my MainActivity a method to see if it is ok

if I ask

        @Override
        public void onResume() {
            super.onResume();
            LiveData<Boolean> IsPremiumPurchased = ((MainActivity)getActivity()).billingDataSource.isPurchased(SKU_PREMIUM);
            mIsPremium = IsPremiumPurchased.getValue();
            Log.d(TAG, "User is " + (mIsPremium ? "PREMIUM" : "NOT PREMIUM"));
            ((MainActivity)getActivity()).updateUi();
        }

I got Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.Boolean.booleanValue()' on a null object reference at com.xxxxxxxxxxx.MainActivity$MainFragment.onResume(MainActivity.java:1302)

because IsPremiumPurchased is not valid

Answer 1

As I see a sample use live-data and data-binding.

From your code:

((MainActivity)getActivity()).billingDataSource.isPurchased(SKU_PREMIUM)

You get live-data object IsPremiumPurchased but live-data provides observe pattern to receive new values. It's means that usually you can't get value sync by calling IsPremiumPurchased.getValue() because operation of getting value by key SKU_PREMIUM is async and will be written to IsPremiumPurchased after some time. That's why call to IsPremiumPurchased.getValue() returns null in your snippet(As you can see it valid behaviour). Right way to use IsPremiumPurchased - is subscribe to updates of IsPremiumPurchased like in this sample. For example you can put code like this to onCreate method:

        final Observer<Boolean> premiumPurchasedObserver = new Observer<Boolean>() {
            @Override
            public void onChanged(@Nullable final Boolean isPurchased) {
                mIsPremium = isPurchased;
               ((MainActivity)getActivity()).updateUi();
            }
        };

        IsPremiumPurchased.observe(this, premiumPurchasedObserver);
        mIsPremium = IsPremiumPurchased.getValue();
        if(mIsPremium == null) {
            mIsPremium = false
        } 
        ((MainActivity)getActivity()).updateUi();
        

I Add check for current value after IsPremiumPurchased.observe call to get consistent ui if premiumPurchasedObserver.onChanged will be called with long delay.