为什么不能显示我的底部导航栏？

Question

Im wondering why my bottom navigation bar is not showing up. Can anyone help me out please. Im still learning Android so i apologise in advance if i seem to be asking the wrong questions!

This is my home.xml file

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/home"
        android:title="Home"
        android:icon="@drawable/ic_action_home"
        />
    <item
        android:id="@+id/Login"
        android:title="Login"
        android:icon="@drawable/ic_action_login"
        />
    <item
        android:id="@+id/About"
        android:title="About"
        android:icon="@drawable/ic_action_about"
        />


</menu>

This is my fragment_home.xml file

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".HomeFragment">

    <!-- TODO: Update blank fragment layout -->

    <ListView
        android:id="@+id/listViewDetails"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />



</LinearLayout>

This is HomeFragment.java file

package sg.edu.rp.c346.a3pdwork;


import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;


/**
 * A simple {@link Fragment} subclass.
 */
public class HomeFragment extends Fragment {


    public HomeFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_home, container, false);
        String[] menuItems = {"Do Something!", "Do something else!", "Do yet another thing!"};

        ListView listView = (ListView) view.findViewById(R.id.listViewDetails);

        ArrayAdapter<String> listViewAdapter = new ArrayAdapter<String>(
          getActivity(),
          android.R.layout.simple_list_item_1,
          menuItems
        );
        listView.setAdapter(listViewAdapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                if (position == 0) {
                    Toast.makeText(getActivity(),"Hi! You CLikced the first item", Toast.LENGTH_LONG).show();
                }else if (position == 1) {
                    Toast.makeText(getActivity(),"Hi! You CLikced the Second item", Toast.LENGTH_LONG).show();
                }else if (position == 2) {
                    Toast.makeText(getActivity(),"Hi! You CLikced the Third item", Toast.LENGTH_LONG).show();

                }

            }
        });

        // Inflate the layout for this fragment
        return view;
    }

}

This is my AndroidManifest.xml file

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="sg.edu.rp.c346.a3pdwork">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity"
            android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

This is LoginFragment.java

package sg.edu.rp.c346.a3pdwork;


import android.graphics.Color;
import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;


/**
 * A simple {@link Fragment} subclass.
 */
public class LoginFragment extends Fragment {
    Button b1, b2;
    EditText ed1, ed2;

    TextView tx1;
    int counter = 3;

    public LoginFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_login, container, false);
        b1 =  findViewByID(R.id.button);
        ed1 =  findViewByID(R.id.editText);
        ed2 =  findViewByID(R.id.editText2);

        b2 = (Button)findViewById(R.id.button2);
        tx1 = (TextView)findViewById(R.id.textView3);
        tx1.setVisibility(View.GONE);

        b1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (ed1.getText().toString().equals("admin") &&
                        ed2.getText().toString().equals("admin")) {
                    Toast.makeText(getApplicationContext(),
                            "Redirecting...", Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(getApplicationContext(), "Wrong Credentials", Toast.LENGTH_SHORT).show();

                    tx1.setVisibility(View.VISIBLE);
                    tx1.setBackgroundColor(Color.RED);
                    counter--;
                    tx1.setText(Integer.toString(counter));

                    if (counter == 0) {
                        b1.setEnabled(false);
                    }
                }
            }
        });
        b2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                finish();
            }
        });
    }
}

This is my fragment_about.xml file

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".AboutFragment">

<!-- TODO: Update blank fragment layout -->
<TextView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:text="@string/hello_blank_fragment" />

</FrameLayout>

This is my fragment_login.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"

    tools:context=".LoginFragment">

    <!-- TODO: Update blank fragment layout -->
    <TextView android:text = "Tutor Seeker"
        android:layout_width="wrap_content"
        android:layout_height = "wrap_content"
        android:id = "@+id/textview"
        android:textSize = "35dp"
        android:layout_alignParentTop = "true"
        android:layout_centerHorizontal = "true" />

    <EditText
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:id = "@+id/editText"
        android:hint = "Enter Name"
        android:focusable = "true"
        android:textColorHighlight = "#ff7eff15"
        android:textColorHint = "#ffff25e6"
        android:layout_marginTop = "46dp"
        android:layout_alignParentLeft = "true"
        android:layout_alignParentStart = "true"
        android:layout_alignParentRight = "true"
        android:layout_alignParentEnd = "true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="textPassword"
        android:ems="10"
        android:id="@+id/editText2"
        android:layout_below="@+id/editText"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignRight="@+id/editText"
        android:layout_alignEnd="@+id/editText"
        android:textColorHint="#ffff299f"
        android:hint="Enter Password" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Attempts Left:"
        android:id="@+id/textView2"
        android:layout_below="@+id/editText2"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:textSize="25dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="New Text"
        android:id="@+id/textView3"
        android:layout_alignTop="@+id/textView2"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:layout_alignBottom="@+id/textView2"
        android:layout_toEndOf="@+id/textview"
        android:textSize="25dp"
        android:layout_toRightOf="@+id/textview" />


    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="login"
        android:id="@+id/button"
        android:layout_alignParentBottom="true"
        android:layout_toLeftOf="@+id/textview"
        android:layout_toStartOf="@+id/textview" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Cancel"
        android:id="@+id/button2"
        android:layout_alignParentBottom="true"
        android:layout_toRightOf="@+id/textview"
        android:layout_toEndOf="@+id/textview" />



</RelativeLayout>

This is my AboutFragment.java file

package sg.edu.rp.c346.a3pdwork;


import android.os.Bundle;

import androidx.fragment.app.Fragment;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;


/**
 * A simple {@link Fragment} subclass.
 */
public class AboutFragment extends Fragment {


    public AboutFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_about, container, false);
    }

}

This is MainActivity.java file

package sg.edu.rp.c346.a3pdwork;

import androidx.appcompat.app.AppCompatActivity;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.NavigationUI;


import android.graphics.Color;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.material.bottomnavigation.BottomNavigationView;

public class MainActivity extends AppCompatActivity {



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


    }
}

This is my activity_main.xml file

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <fragment
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:id="@+id/nav_host_fragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph" />
    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottom_nav"
        app:menu="@menu/home"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />
</LinearLayout>

Answer 1

Try to use RelativeLayout instead of LinearLayout like below:

<RelativeLayout 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=".MainActivity">

    <fragment
        android:name="androidx.navigation.fragment.NavHostFragment"
        ... />

    <com.google.android.material.bottomnavigation.BottomNavigationView
        ...
        android:layout_alignParentBottom="true"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        />
</RelativeLayout>

Answer 2

The fragment in your activity_main has android:layout_height="match_parent" and LinearLayout has vertical orientation. This means that your fragment takes all the place on the screen and your bottom navigation menu placed below your fragment. Also, you shouldn't set navigation menu height as match_parent . I suggest you to try to use ConstraintLayout as layout root. NOTE! I use AndroidX, but it also works for AppCompat.

<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:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent">

<com.google.android.material.bottomnavigation.BottomNavigationView
    android:id="@+id/bottomNavigationView"
    android:layout_width="match_parent"
    android:layout_height="@dimen/bottom_menu_height"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:menu="@menu/navigation" />
<fragment
    android:id="@+id/fragment"
    android:layout_width="0dp"
    android:layout_height="0dp"
    app:layout_constraintBottom_toTopOf="@+id/bottomNavigationView"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>