08.BottomNavigationView+ViewPager底部栏滑动

参考:https://www.jianshu.com/p/0ba25cc65889

step1. create a project,导入依赖：

compile'com.android.support:design:26.1.0'  
compile'com.android.support:support-v4:26.1.0'

step2. 在res下新建menu文件夹，新建一个menu菜单下的navigation.xml文件：

step3. 主布局文件activity_main.xml:

step4.创建5个Fragment与其对应的Activity,此处略过...
step5.添加适配器：

public class ViewPagerAdapter extends FragmentPagerAdapter {

    private List list;
    

    public ViewPagerAdapter(FragmentManager fm, List fragments) {
        super(fm);
        list=fragments;
    }

    @Override
    public Fragment getItem(int position) {
        return list.get(position);
    }

    @Override
    public int getCount() {
        return list.size();
    }
}

step6.完整的activity文件:

public class MainActivity extends AppCompatActivity {

    private ViewPager viewPager;
    private BottomNavigationView navigation;

    private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
            = new BottomNavigationView.OnNavigationItemSelectedListener() {

        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.first:
                    viewPager.setCurrentItem(0);
                    return true;
                case R.id.two:
                    viewPager.setCurrentItem(1);
                    return true;
                case R.id.third:
                    viewPager.setCurrentItem(2);
                    return true;
                case R.id.four:
                    viewPager.setCurrentItem(3);
                    return true;
                case R.id.five:
                    viewPager.setCurrentItem(4);
                    return true;
            }
            return false;
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        supportRequestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);

        navigation = (BottomNavigationView) findViewById(R.id.navigation);
        viewPager = (ViewPager)findViewById(R.id.viewPager);

        //默认 >3 的选中效果会影响ViewPager的滑动切换时的效果，故利用反射去掉
        BottomNavigationViewHelper.disableShiftMode(navigation);
        navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);


        // 为ViewPager添加页面改变事件
        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                // 将当前的页面对应的底部标签设为选中状态
                navigation.getMenu().getItem(position).setChecked(true);
            }
            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
        setupViewPager(viewPager);
    }

    private void setupViewPager(ViewPager viewPager){
        //构造适配器
        List fragments=new ArrayList();
        fragments.add(new firstFragment());
        fragments.add(new twoFragment());
        fragments.add(new thirdFragment());
        fragments.add(new fourFragment());
        fragments.add(new fiveFragment());
        //设定适配器
        ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager(),fragments);
        viewPager.setAdapter(adapter);
    }
}

step7.BottomNavigationView默认有个放大的ShiftingMode效果，但是尚未支持代码层级的切换。在3个menu item及以下时默认关闭，而到了4个及以上时就懵逼了，因为我们是要做ViewPager的侧滑啊！
所以代码如下：

// 利用反射，改变 item 中 mShiftingMode 的值
public class BottomNavigationViewHelper {

    public static void disableShiftMode(BottomNavigationView navigationView) {

        BottomNavigationMenuView menuView = (BottomNavigationMenuView) navigationView.getChildAt(0);
        try {
            Field shiftingMode = menuView.getClass().getDeclaredField("mShiftingMode");
            shiftingMode.setAccessible(true);
            shiftingMode.setBoolean(menuView, false);
            shiftingMode.setAccessible(false);

            for (int i = 0; i < menuView.getChildCount(); i++) {
                BottomNavigationItemView itemView = (BottomNavigationItemView) menuView.getChildAt(i);
                itemView.setShiftingMode(false);
                itemView.setChecked(itemView.getItemData().isChecked());
            }

        } catch (NoSuchFieldException | IllegalAccessException e) {
            e.printStackTrace();
        }
    }
}