用CoordinatorLayout 实现 toolbar 隐藏效果

效果如下图

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"


    >

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"

        >

        <android.support.v7.widget.Toolbar

            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:layout_scrollFlags="scroll|enterAlways"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:tabIndicatorColor="#ADBE107E"
            app:tabMode="scrollable" />

    </android.support.design.widget.AppBarLayout>


    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">


    </android.support.v4.view.ViewPager>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/btn"
        android:layout_width="132dp"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:clickable="true"
        android:src="@mipmap/ic_launcher"
        app:layout_anchor="@id/viewpager"
        app:layout_anchorGravity="bottom|right|end" />


</android.support.design.widget.CoordinatorLayout>

上面是MainActivity的xml布局

MainActivity

public class Main2Activity extends AppCompatActivity {
    private ViewPager viewPager;
    private TabLayout tabLayout;
    FloatingActionButton floatingActionButton;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        floatingActionButton = findViewById(R.id.btn);
        floatingActionButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Snackbar.make(v, "you onclick", Snackbar.LENGTH_SHORT).show();
            }
        });


        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        final ActionBar ab = getSupportActionBar();
        ab.setDisplayHomeAsUpEnabled(true);
        viewPager = findViewById(R.id.viewpager);
        initViewpager();
    }

    private void initViewpager() {
        tabLayout = findViewById(R.id.tabs);
        List<String> list = new ArrayList<>();
        list.add("精选");
        list.add("体育");
        list.add("购物");
        list.add("精选1");
        list.add("精选2");
        list.add("精选3");
        list.add("精选4");
        list.add("精选5");
        list.add("精选6");
        list.add("精选7");
        list.add("精选8");
        for (int i = 0; i < list.size(); i++) {

            tabLayout.addTab(tabLayout.newTab().setText(list.get(i)));
        }

        List<Fragment> fragments = new ArrayList<>();

        for (int i = 0; i < list.size(); i++) {
            fragments.add(new com.example.cnb.coordinatorlayout_toolbar.ListFragment());
        }

        FragmentAdapter fragmentAdapter = new FragmentAdapter(getSupportFragmentManager(), fragments, list);

        viewPager.setAdapter(fragmentAdapter);

        tabLayout.setupWithViewPager(viewPager);

        tabLayout.setTabsFromPagerAdapter(fragmentAdapter);

    }
}