java - 在模拟器中运行后不出现BottomNavigationView

Question

我的BottomNavigationView出现在android studio的预览中，但是当我在模拟器中运行它时它没有出现，所以它只是出现在模拟器中的 fragment ，并且程序没有给我任何错误，所以我尝试切换主页布局也没有出现!

这是我的代码

在 Home_activity xml 中

public class HomeActivity extends AppCompatActivity {

@Override
public void onCreate(@Nullable Bundle savedInstanceState, @Nullable PersistableBundle persistentState) {
    super.onCreate(savedInstanceState, persistentState);
    setContentView(R.layout.activity_home);

    BottomNavigationView bottomNavigationView =findViewById(R.id.nav_view);
    bottomNavigationView.setOnNavigationItemSelectedListener(navlistener);


}

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

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
        Fragment selectedFragment =null;

        switch (menuItem.getItemId()){

            case R.id.navigation_home:
                selectedFragment=new Home_fragment();
                break;

                case R.id.navigation_dashboard:
                selectedFragment=new Dashboard_fragment();
                break;



            case R.id.navigation_notifications:
                selectedFragment=new Notificatons_fragment();
                break;
        }

        //to show them

        getSupportFragmentManager().beginTransaction().replace(R.id.nav_host_fragment,selectedFragment).commit();

        return true;
    }
};

}

在主页布局页面的 xml 中

 <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingTop="?attr/actionBarSize">

  <fragment
      android:id="@+id/nav_host_fragment"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:layout_above="@id/nav_view"/>

    <com.google.android.material.bottomnavigation.BottomNavigationView
      android:id="@+id/nav_view"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_alignParentBottom="true"
      app:menu="@menu/bottom_nav_menu"

      />

</RelativeLayout>

Answer 1

Add library in gradle file

dependencies {
   implementation 'com.google.android.material:material:1.1.0'
}

Xml file without fragment tag. fragment is giving error on my side.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingTop="?attr/actionBarSize">


    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:layout_alignParentBottom="true"
        app:menu="@menu/bottom_nav_menu"

        />

</RelativeLayout>

bottom_nav_menu.xml file in menu folder in res

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/home"
        android:icon="@android:drawable/arrow_down_float"
        android:title="home" />
    <item
        android:id="@+id/id1"
        android:icon="@android:drawable/btn_plus"
        android:title="deeplink" />
</menu>

You can change your custom icons in menu. Try it. Hopefully, may resolve you issue your issue. I have tested it on Android Q emulator. Thanks in advance.