CODEWITHSUNDEEP
androidfragment
Choletski
Choletski

Reputation: 7515

How to access viewpager's fragment from activity

Suppose such an scenario, we have an activity and 3 fragments, like so: MyActivity Frg1, Frg2 and Frg3. Frg2 and Frg3 are embedded into a viewPager. My needs is to trigger Frg2 from Frg1. I made an interface TriggerActivityFromFrg1 and MyActivity implements it, when press button in Frg1 I call (getActivity) triggerActivityFromFrg1.trigger() and method trigger() is called in MyActivity, the problem is how to trigger Frg2 from activity?

I'd like to make somehow an interface between MyActivity and Frg2.

p.s. I don't want to use eventbus.

Upvotes: 0

Views: 204

Answers (1)

kris larson
kris larson

Reputation: 30985

  1. Have your Frg2 class also implement the interface:

    public class Frg2 extends Fragment implements TriggerActivityFromFrg1 {

    and implement the method

        @Override
    public void trigger() {
        if (getView() != null) {  // see comments below
            // TODO logic here
        }
    }

  2. Add a field to your activity to keep track of the target fragment:

        private TriggerActivityFromFrg1 mTarget;

  3. Add the register/unregister methods to the activity:

        public synchronized void registerTriggerTarget(TriggerActivityFromFrg1 listener) {
        mTarget = listener;
    }

    public synchronized void unregisterTriggerTarget(TriggerActivityFromFrg1 listener) {
        if (mTarget == listener) {
            mTarget = null;
        }
    }

  4. Make the trigger method in your activity like this:

        public void trigger() {
        if (mTarget != null) {
            mTarget.trigger();
        }
    }

  5. Override onAttach() and onDetach() in Frg2 to register/unregister:

        @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        ((MyActivity) activity).registerTriggerTarget(this);
    }

    @Override
    public void onDetach() {
        ((MyActivity) getActivity()).unregisterTriggerTarget(this);
        super.onDetach();
    }

Congratulations, you just built your own mini event bus.

There's a reason you have to add all this code, and that's because ViewPager won't create fragments until it needs them. Also it decouples MyActivity from Frg2.

Another thing to keep in mind if extending FragmentPagerAdapter is that the fragment will stay in memory even if the view is destroyed, so make sure you check that the fragment has a valid view, i.e. if (getView() != null)

Upvotes: 1

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