ViewPager中的片段问题

Question

I have 3 Fragments inside a ViewPager . For each Fragment I set a different NavigationBar color (programmatically). This is the code.

@Override
    public void init(Bundle arg0) {
        // TODO Auto-generated method stub
        addSlide(new Fragment1());
        addSlide(new Fragment2());
        addSlide(new Fragment3());

    }


    private class Fragment1 extends Fragment {

        @Override
        public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
             if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {                
                    getWindow().setNavigationBarColor(Color.parseColor(BLUE));
            }
            Log.e("test", "1");
            return inflater.inflate(R.layout.layout_intro, container, false);
        }

    }

    private class Fragment2 extends Fragment {

        @Override
        public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
             if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {                
                    getWindow().setNavigationBarColor(Color.parseColor(RED));
            }
                Log.e("test", "2");

            return inflater.inflate(R.layout.layout_intro_2, container, false);
        }

    }

    private class Fragment3 extends Fragment {

        @Override
        public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
             if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {                
                    getWindow().setNavigationBarColor(Color.parseColor(GREEN));
            }
                Log.e("test", "3");

            return inflater.inflate(R.layout.layout_intro_3, container, false);
        }

    }

} 

In Logcat I see wrong numbers. For example i'm in the first Fragment and I see GREEN NavigationBar and "2". Why? How can i solve?

Answer 1

This happens because the ViewPager loads already the next fragment, so if you are on fragment one, fragment 2 is already created, if you swipe to fragment 2, fragment 3 will be created. That's why swiping is smooth.

Todo what you want you need to add onPageChangeListener to your ViewPager like this:

mViewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

            @Override

        public void onPageSelected(int position) {
            switch(position) {
                case 1: if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {                
                      getWindow().setNavigationBarColor(Color.parseColor(BLUE));
                    }
                    break;    
                case 2: if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {                
                      getWindow().setNavigationBarColor(Color.parseColor(RED));
                    }
                    break;    
                case 3: if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {                
                      getWindow().setNavigationBarColor(Color.parseColor(GREEN));
                    }
                    break;    
            }
        }

        @Override
        public void onPageScrolled(int position, float offset, int offsetPixel) {
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    });

and so on.