MainActivity

package com.example.lianxi7;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.RadioGroup;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    private ViewPager pager;
    private RadioGroup group;
    private List<Fragment> list;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        pager = findViewById(R.id.pager);
        group = findViewById(R.id.group);
        list = new ArrayList<>();
        list.add(new FragmentOne());
        list.add(new FragmentTwo());

      FragmentAdapter adapter = new FragmentAdapter(getSupportFragmentManager(),this,list);
        pager.setAdapter(adapter);

        pager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                    switch (position){
                        case 0:
                            group.check(R.id.but1);
                            break;
                        case 1:
                            group.check(R.id.but2);
                            break;

                            default:
                                break;
                    }
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
            group.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
                @Override
                public void onCheckedChanged(RadioGroup group, int checkedId) {
                    switch (checkedId){
                        case R.id.but1:
                            pager.setCurrentItem(0);
                            break;
                        case R.id.but2:
                            pager.setCurrentItem(1);
                            break;

                            default:
                                break;
                    }
                }
            });
    }
}