如何为ViewPager提供许多片段并避免错误代码？

Question

I have 20 FragmentActivity, they all represent like the game screens with different mechanics. I want to put them all in ViewPager. The only thing that comes to mind is this dummy code:

 public static class MyAdapter extends FragmentPagerAdapter {


    @Override
    public Fragment getItem(int position) {
        switch(position){
          case 0:
            return new Fragment1();
          case 1:
            return new Fragment2();
          .........................
          another 20 case statements here
          .........................
          case 20:
            return new Fragment21();
        }
    }

 }

But there should be another way to do it. Will appreciate any help.

Answer 1

FragmentPagerAdapter is smart enough to no instantiate fragments every time they are needed. So you code is OK. That said, 20 fragments kept in memory might be a bit too much. Have a look at FragmentStatePagerAdapter , it will save and restore fragments automatically, without keeping them live in memory all the time.

Instead of using a switch you can have a list of fragments and return from the list:

List<Fragment> fragments;

public Fragment getItem(int pos) {
  return fragments.get(pos);
}

public void addFragment(Fragment f) {
  fragments.add(f);
}

Answer 2

Use FragmentStatePagerAdapter instead of FragmentPagerAdapter .

FragmentStatePagerAdapter is using ArrayList to store fragments, but FragmentPagerAdapter is using getFragmentByTag .

Answer 3

I don't think there's anything very wrong with that to be honest, you see that kinda thing in lots of games where you have like a Menu, Game, Pause, Game Over etc screens.

What I would say though is whether you actually need to create a 'new' Fragment each time you change to a different page.