Android开发：如何让Fragment内容显示在Toolbar与底部导航栏之间

我是Android应用开发新手，希望将fragment_home.xml中的LinearLayout显示在顶部Toolbar和底部导航栏之间，但目前该布局显示在Toolbar上方，无法调整至下方。

相关代码 #

fragment_home.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:layout_height="match_parent"
    tools:context=".ui.home.HomeFragment">

    <LinearLayout
        android:id="@+id/fragment_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent">

        <include
            layout="@layout/recent_message"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="10dp" />

        <include
            layout="@layout/recent_message"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />

    </LinearLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

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"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#262626">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/purple_500"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
        app:layout_constraintTop_toTopOf="parent"
        app:title="@string/username"
        app:titleTextColor="@color/black">

        <ImageView
            android:layout_width="40dp"
            android:layout_height="40dp"
            android:id="@+id/userIconToolbar"
            android:layout_alignParentEnd="true"
            android:layout_gravity="end"
            android:layout_marginEnd="10dp"
            android:clickable="true"
            android:src="@drawable/user_pb_default" />
    </androidx.appcompat.widget.Toolbar>


    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:background="#404040"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu"
        app:itemTextColor="@drawable/bottom_nav_item_color"
        app:itemIconTint="@drawable/bottom_nav_item_color"
        app:labelVisibilityMode="labeled" />

    <fragment
        android:id="@+id/nav_host_fragment_activity_main"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0"
        app:navGraph="@navigation/mobile_navigation" />

</androidx.constraintlayout.widget.ConstraintLayout>

HomeFragment.java #

public class HomeFragment extends Fragment {

    private FragmentHomeBinding binding;

    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        HomeViewModel homeViewModel = new ViewModelProvider(this).get(HomeViewModel.class);

        binding = FragmentHomeBinding.inflate(inflater, container, false);
        View root = binding.getRoot();

        return root;
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        binding = null;
    }
}

MainActivity.java #

public class MainActivity extends AppCompatActivity {

    private ActivityMainBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        binding = ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        toolbarUserIconClick();

        BottomNavigationView navView = findViewById(R.id.nav_view);

        AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(R.id.navigation_home, R.id.navigation_direct, R.id.navigation_groups, R.id.navigation_settings).build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_activity_main);
        NavigationUI.setupWithNavController(binding.navView, navController);
    }

    public void toolbarUserIconClick()
    {
        ImageView imageView = (ImageView) findViewById(R.id.userIconToolbar);
        imageView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //Link To Profile Settings Here
                Toast.makeText(getBaseContext(), "Hello World", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

当前效果 #

解决方法 #

问题核心是activity_main.xml中NavHostFragment的约束设置错误，导致Fragment内容覆盖Toolbar区域，修改步骤如下：

1. 调整NavHostFragment的顶部约束：将app:layout_constraintTop_toTopOf="parent"改为app:layout_constraintTop_toBottomOf="@id/toolbar"，让Fragment区域被限制在Toolbar下方。
2. 移除多余的垂直偏移属性：删除app:layout_constraintVertical_bias="1.0"，避免Fragment内容偏向底部。

修改后的NavHostFragment代码：

<fragment
    android:id="@+id/nav_host_fragment_activity_main"
    android:name="androidx.navigation.fragment.NavHostFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:defaultNavHost="true"
    app:layout_constraintBottom_toTopOf="@id/nav_view"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toBottomOf="@id/toolbar"
    app:navGraph="@navigation/mobile_navigation" />

另外，为了让fragment_home.xml中的LinearLayout布局更合理，可以给它添加顶部约束，绑定到父布局顶部：

<LinearLayout
    android:id="@+id/fragment_view"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">

完成以上修改后，LinearLayout就会正确显示在Toolbar和底部导航栏之间的区域。

内容的提问来源于stack exchange，提问作者Zagro