升级Material1.6.1后BottomNavigationView inflateMenu空指针崩溃

问题现象 #

• 操作场景：向BottomNavigationView中动态加载菜单时触发崩溃
• 触发条件：将Material依赖从com.google.android.material:material:1.2.1升级到com.google.android.material:material:1.6.1后出现，相同代码在1.2.1版本运行无异常
• 崩溃位置：调用bottomNavigationView.inflateMenu(R.menu.menu_bottom_navigation)时抛出异常
• 核心报错：java.lang.NullPointerException: Attempt to invoke virtual method 'int android.view.ViewGroup.getPaddingBottom()' on a null object reference

复现代码 #

MainActivity 逻辑 #

public class MainActivity extends AppCompatActivity {
    private final BottomNavigationView.OnNavigationItemSelectedListener bottomNavListener = item -> {
        // 选中逻辑省略
        return true;
    }
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        BottomNavigationView bottomNavigationView = findViewById(R.id.bottom_navigation);
        bottomNavigationView.setItemIconTintList(null);
        bottomNavigationView.setOnNavigationItemSelectedListener(bottomNavListener);
        bottomNavigationView.getMenu().clear();
        bottomNavigationView.inflateMenu(R.menu.menu_bottom_navigation); // 崩溃触发行
    }
}

菜单资源 menu_bottom_navigation.xml #

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/bottom_nav_home"
        android:icon="@drawable/bottom_nav_home_icon_selector"
        android:title="@string/home_title" />
    <item
        android:id="@+id/bottom_nav_screen2"
        android:icon="@drawable/bottom_nav_screen2_icon_selector"
        android:title="@string/savings_screen2" />
    <item
        android:id="@+id/bottom_nav_screen3"
        android:icon="@drawable/bottom_nav_screen3_icon_selector"
        android:title="@string/screen3_title" />
    <item
        android:id="@+id/bottom_nav_screen4"
        android:icon="@drawable/bottom_nav_screen4_icon_selector"
        android:title="@string/screen4_title" />
    <item
        android:id="@+id/bottom_nav_screen5"
        android:icon="@drawable/bottom_nav_screen5_icon_selector"
        android:title="@string/screen5_title" />
</menu>

布局资源 activity_main.xml #

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:layout_width="match_parent"
    android:id="@+id/layout"
    android:layout_height="match_parent"
    tools:context=".ui.main.MainActivity">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/main_fragment_container"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        app:layout_constraintBottom_toTopOf="@+id/bottom_navigation"
        app:layout_constraintTop_toTopOf="parent" />

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottom_navigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:itemTextAppearanceActive="@style/BottomNavigationView.Active"
        app:itemTextAppearanceInactive="@style/BottomNavigationView"
        app:itemTextColor="@drawable/bottom_nav_selector"
        app:labelVisibilityMode="labeled"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/main_fragment_container" />

</androidx.constraintlayout.widget.ConstraintLayout>

完整崩溃日志 #

2022-06-14 19:49:18.562 18439-18439/com.example.android.debug E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.android.debug, PID: 18439
    java.lang.RuntimeException: Unable to start activity 
    ComponentInfo{com.example.android.debug/com.example.android.ui.main.MainActivity}: 
    java.lang.NullPointerException: Attempt to invoke virtual method 'int 
    android.view.ViewGroup.getPaddingBottom()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

问题根因 #

从Material库1.4.0版本开始，BottomNavigationView调整了内部菜单容器的初始化逻辑：调用getMenu().clear()清空菜单时，内部承载菜单项的导航条容器会被临时移除回收，后续如果同步调用inflateMenu()，新版本逻辑会直接访问还未重新创建的导航条容器，调用其getPaddingBottom()方法时触发空指针。
1.2.1版本不存在这个问题是因为旧版本clear操作不会销毁内部容器，inflate时可以正常访问。

修复方案 #

两种方案选其一即可：

• 方案一（推荐）：删除多余的bottomNavigationView.getMenu().clear()调用。inflateMenu()方法本身在加载新菜单前就会自动清空原有菜单，不需要手动提前清空，修改后的代码兼容所有版本的Material库。
• 方案二：如果业务逻辑确实需要先手动清空菜单，将inflate操作post到视图消息队列，等内部状态更新完成后再执行加载：

  bottomNavigationView.getMenu().clear();
  bottomNavigationView.post(() -> {
      bottomNavigationView.inflateMenu(R.menu.menu_bottom_navigation);
  });
  

补充提示：当前菜单配置了5个item，升级到更高版本Material库如果出现文字位移、选中项放大异常，可以在布局中给BottomNavigationView添加app:itemHorizontalTranslationEnabled="false"属性，关闭水平位移动画，保持所有item样式统一。

内容的提问来源于stack exchange，提问作者Sumit Jain