android - 如何在 BottomNavigationView 中设置所选项目

Question

我正在尝试在创建的 Activity 上设置默认项目，但它不起作用？
这是我的代码:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_userhome);
    mTextMessage = (TextView) findViewById(R.id.message);
    profile = (FrameLayout) findViewById(R.id.profile);
    mall = (FrameLayout) findViewById(R.id.mall);
    dietplan =(FrameLayout) findViewById(R.id.dietplan);
    BottomNavigationView navigation = (BottomNavigationView) 
    findViewById(R.id.navigation);
    navigation.setSelectedItemId(R.id.dietplan);
     navigation.setOnNavigationItemSelectedListener 
    (mOnNavigationItemSelectedListener);
}

但似乎 navigation.setSelectedItemId(R.id.dietplan);不管用。请帮我设置底部导航栏的默认项:

这是我的堆栈跟踪(logcat):

FATAL EXCEPTION: main
   Process: gym.android.ommsoftware.gym, PID: 1915
   java.lang.RuntimeException: Unable to start activity ComponentInfo{gym.android.ommsoftware.gym/gym.android.ommsoftware.gym.Userhome}: java.lang.NullPointerException
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2404)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2464)
       at android.app.ActivityThread.access$900(ActivityThread.java:172)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308)
       at android.os.Handler.dispatchMessage(Handler.java:102)
       at android.os.Looper.loop(Looper.java:146)
       at android.app.ActivityThread.main(ActivityThread.java:5653)
       at java.lang.reflect.Method.invokeNative(Native Method)
       at java.lang.reflect.Method.invoke(Method.java:515)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
       at dalvik.system.NativeStart.main(Native Method)
    Caused by: java.lang.NullPointerException
       at gym.android.ommsoftware.gym.Userhome.onCreate(Userhome.java:57)
       at android.app.Activity.performCreate(Activity.java:5541)
       at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1093)
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2368)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2464) 
       at android.app.ActivityThread.access$900(ActivityThread.java:172) 
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308) 
       at android.os.Handler.dispatchMessage(Handler.java:102) 
       at android.os.Looper.loop(Looper.java:146) 
       at android.app.ActivityThread.main(ActivityThread.java:5653) 
       at java.lang.reflect.Method.invokeNative(Native Method) 
       at java.lang.reflect.Method.invoke(Method.java:515) 
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291) 
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107) 
       at dalvik.system.NativeStart.main(Native Method) 

Answer 1

而不是选中你需要setChecked(true)那个项目。试试这个代码

mBottomNavigationView=(BottomNavigationView)findViewById(R.id.bottom_nav);
mBottomNavigationView.getMenu().findItem(R.id.item_id).setChecked(true);

选中的项目在 BottomNavigationView 中突出显示.