Android从片段中检测ViewPager上的OnPageChangeListener

Question

Hi i have a ViewPager that has creates a fragment for each page using a fragment adapter. On each fragment i have an ImageView that i want to animate everytime that page appears on screen.

My ViewPager currently preloads the 1st 2 pages so the animation doesn't run on those but it does work on the 3rd page. I have added an onPageChangedListener but not sure how to implement it so it talks to my fragment adapter and runs the animation. Does anyone know either how to correctly detect a page change from within a fragment or a way to disable the page preloading in a memory management efficient way?

heres what i have tried so far

heres my activity with the ViewPager

public void getAdapter(){
         CustomViewPager pager = (CustomViewPager) findViewById(R.id.tutorialPager);
         pager.setPagingEnabled(true);
         pager.setOffscreenPageLimit(-1);
         adapterViewPager = new MyPagerAdapter(getSupportFragmentManager(),this);
         pager.setAdapter(adapterViewPager);
         CirclePageIndicator Indicator = (CirclePageIndicator)findViewById(R.id.circles);
         Indicator.setViewPager(pager);

    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.layout_tutorial_view);
        getAdapter();
        extras = getIntent().getExtras();
    }


        public static class MyPagerAdapter extends FragmentPagerAdapter {

            private Context context;

            public MyPagerAdapter(android.support.v4.app.FragmentManager fragmentManager,Context c) {

                super(fragmentManager);
                context = c;
            }


            @Override
            public int getCount() {
                int levelCount = 4;
                return levelCount;
            }

            // Returns the fragment to display for that page
            @Override
            public TutorialAdapter getItem(int position) {
                String data = null;

                return TutorialAdapter.newInstance(position, data, context);

            }


            @Override
            public CharSequence getPageTitle(int position) {
                return "Page " + position;
            }

        }

       public static class onPageChangedListener implements OnPageChangeListener {

        @Override
        public void onPageScrollStateChanged(int arg0) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onPageSelected(int arg0) {
            // TODO Auto-generated method stub

        }

       }

    }

heres my fragment adapter inside my onCreateView

if(page == 1){
                view = inflater.inflate(R.layout.layout_tutorial, container, false);


                tutImage = (ImageView)view.findViewById(R.id.tutImage);
                int imageResource = getResources().getIdentifier("tut_view_2", "drawable", context.getPackageName());
                Drawable tutImageDrawable = getResources().getDrawable(imageResource);
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                    tutImage.setBackground(tutImageDrawable);
                }else{
                    tutImage.setBackgroundDrawable(tutImageDrawable);
                }

                Animation AniMoveUp = AnimationUtils.loadAnimation(context, R.anim.tut_image);  
                tutImage.startAnimation(AniMoveUp);

Answer 1

Here is an example Android application that extends the Fragment Life Cycle with two new methods: onResumeViewPage() and onPauseViewPage(). If you put your animation code in onResumeViewPage() it should work.

See: Slider Android Application in BitBucket.

Answer 2

Move your startAnimation call to the onResume method of the Fragments. That way the animation will start when the Fragment is visible. See Fragment LifeCycle for more detailed explanation.