BottomNavigationView控制fragment跳转

实现BottomNavigationView控制fragment跳转比较简单，直接在相关路径下右键/new/Activity/Bottom Navigation Activity，便会自动生成相关内容，然后根据需求修改即可。

一、生成相关文件

1）Activity

app:menu="@menu/bottom_nav_menu" 关联导航按钮菜单内容；android:name=“androidx.navigation.fragment.NavHostFragment” 设置Fragment容器；app:defaultNavHost=“true” 把系统后退按钮连接到NavHostFragment；
app:navGraph="@navigation/mobile_navigation" 将NavHostFragment和导航图关联起来。

2）menu/bottom_nav_menu
设置导航按钮菜单内容，id、icon、title

3）navigation/mobile_navigation
navigation资源文件，绑定对应的Fragment
app:startDestination="@+id/navigation_home" 设置开始加载的第一个Fragment
注意：fragment里面的id一定要跟menu资源文件item的id相一致，否则会出现BottomNavigationView按钮无法点击的问题

4）MainActivity实现功能

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        BottomNavigationView navView = findViewById(R.id.nav_view);
        //获取ActionBar设置，
        // 通过NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);设置ActionBar的title
        //如果不显示ActionBar可以注析掉
        AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
                R.id.navigation_home, R.id.navigation_dashboard, R.id.navigation_notifications)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        //设置ActionBar的title，如果主题不含有ActionBar会报错
        NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
        //设置导航控制
        NavigationUI.setupWithNavController(navView, navController);
    }

}

二、其他相扩展

1）BottomNavigationView的item超过三个title不显示
这个问题解决比较简单

navView.setLabelVisibilityMode(LabelVisibilityMode.LABEL_VISIBILITY_LABELED);

2）需要在BottomNavigationView添加小红点

//获取item视图，然后再给视图添加上对应的布局内容
        //0代表是在第一个item上面添加小红点
        BottomNavigationMenuView menuView = (BottomNavigationMenuView) navView.getChildAt(0);
        View tab = menuView.getChildAt(0);
        BottomNavigationItemView itemView = (BottomNavigationItemView) tab;
        View badge = LayoutInflater.from(this).inflate(R.layout.view_red_tag, menuView, false);
        int dp8 = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 14, getResources().getDisplayMetrics());
        BottomNavigationItemView.LayoutParams params = new BottomNavigationItemView.LayoutParams(dp8, dp8);
        params.gravity = Gravity.CENTER_HORIZONTAL;
        params.leftMargin = dp8;
        params.topMargin = 0;
        itemView.addView(badge, params);
        TextView tvBadgeCount = badge.findViewById(R.id.tv_tag_num);
        RelativeLayout rlBadge = badge.findViewById(R.id.rl_red_tag);
        rlBadge.setGravity(Gravity.CENTER_HORIZONTAL);