viewpage和tablayout导航栏

引入material库:

implementation 'com.google.android.material:material:1.2.1'

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
android:orientation="vertical"
    android:layout_height="match_parent">

        <com.google.android.material.tabs.TabLayout
            android:id="@+id/tab_layout"
            android:layout_width="match_parent"
            android:layout_height="40dp"
            android:layout_gravity="center_horizontal">

        </com.google.android.material.tabs.TabLayout>


    <androidx.viewpager.widget.ViewPager
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>




</LinearLayout>

public class MainActivity extends AppCompatActivity {

    private ViewPager viewPager;

    private TabLayout tabLayout;

    private ViewPagerAdapter pagerAdapter;
            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.activity_main);

                    pagerAdapter = new ViewPagerAdapter(getSupportFragmentManager() );
                    viewPager = (ViewPager) findViewById(R.id.view_pager);
                    viewPager.setAdapter(pagerAdapter);
                    tabLayout  =  findViewById(R.id.tab_layout);

                    tabLayout.setupWithViewPager(viewPager);
                    tabLayout.setTabMode(TabLayout.MODE_FIXED);
                }



    }

public class ViewPagerAdapter extends FragmentPagerAdapter {
   private String[] title = {"我的", "发现", "朋友"};
    public ViewPagerAdapter(FragmentManager fm) {
        super( fm);

    }


    @Override
    public Fragment getItem(int i) {

        switch (i) {
            case 0:
                return new Fragment1();
            case 1:
                return new Fragment2();
            case 2:
                return new Fragment3();

        }
        return null;
    }

    @Override
    public int getCount() {
        return title.length;
}

    @Nullable
    @Override
    public CharSequence getPageTitle(int position) {

        return title[position];
    }
}