viewpager加fragment可滑动加radio跟随滑动

public class MainActivity extends AppCompatActivity implements RadioGroup.OnCheckedChangeListener, ViewPager.OnPageChangeListener {
    private ArrayList<Fragment> arrayList;
    private FragmentManager manager;
    private RadioGroup radioGroup;
    private RadioButton[] radioButtons;
    private ViewPager viewPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewPager= (ViewPager) findViewById(R.id.main_vp);
        radioGroup= (RadioGroup) findViewById(R.id.main_rg);
        manager=getSupportFragmentManager();
        arrayList=new ArrayList<>();
        Fragment1 fragment1=new Fragment1();
        Fragment2 fragment2=new Fragment2();
        Fragment3 fragment3=new Fragment3();
        Fragment4 fragment4=new Fragment4();
        Fragment5 fragment5=new Fragment5();
        arrayList.add(fragment1);
        arrayList.add(fragment2);
        arrayList.add(fragment3);
        arrayList.add(fragment4);
        arrayList.add(fragment5);
        Main_Adapter adapter=new Main_Adapter(manager,arrayList);
        viewPager.setAdapter(adapter);
        radioButtons=new RadioButton[radioGroup.getChildCount()];
        for (int i = 0; i < radioButtons.length; i++) {
            radioButtons[i]= (RadioButton) radioGroup.getChildAt(i);
        }
        radioButtons[0].setChecked(true);
        radioGroup.setOnCheckedChangeListener(this);
        viewPager.setOnPageChangeListener(this);
    }

    @Override
    public void onCheckedChanged(RadioGroup radioGroup, int checkedId) {
        for (int j = 0; j < radioButtons.length; j++) {
            if (radioButtons[j].getId()==checkedId){
                viewPager.setCurrentItem(j);
            }

        }
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    @Override
    public void onPageSelected(int position) {
        radioButtons[position].setChecked(true);
    }

    @Override
    public void onPageScrollStateChanged(int state) {

    }
}