viewPager.setAdapter(new MyFragmentPagerAdapter(getSupportFragmentManager()

Null Pointer Exeception on viewPager.setAdapter(new MyFragmentPagerAdapter(getSupportFragmentManager(),alFragment)); viewPager未初期化you can debug a Null PointerException yourself by adding things like:

if(viewPager == null){ Log.e("MainActivity", "viewPager should not be null"); }