App crashes when I switch to an activity that contains a fragment (Binary XML file line #10: Binary XML file line #10: Error inflating class fragment)

Question

My app crashes when I press a button to open another activity that contains a fragment. I am new to Android Studio and I can't seem to find any solution.

In the activity_main.xml I removed the other buttons for this question because I want to focus mainly on this monday_btn.

I researched this type of error and tried many tips but none of them seemed to work.

MainActivity.java

    package com.example.dietmanagement;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentTransaction;

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {



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

        /*Intent i = getIntent();
        String current_user = i.getStringExtra("current_user");
        TextView current_user_txtview = findViewById(R.id.current_user);
        current_user_txtview.setText("Welcome, " + current_user);*/

        Button monday = findViewById(R.id.monday_btn);
        monday.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent day = new Intent(MainActivity.this, DayActivity.class);

                startActivity(day);
            }
        });

    }

}

DayActivity.java

    package com.example.dietmanagement;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentTransaction;

import android.content.Intent;
import android.os.Bundle;

public class DayActivity extends AppCompatActivity {



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

        FragmentTransaction fragmentTransaction;
        fragmentTransaction = getSupportFragmentManager().beginTransaction();
        DayFragment dayFragment = new DayFragment();
        fragmentTransaction.add(R.id.dayfragment, dayFragment);
        fragmentTransaction.commit();


    }
}

DayFragment.java

    package com.example.dietmanagement;

import android.os.Bundle;

import androidx.fragment.app.Fragment;

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


public class DayFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view =  inflater.inflate(R.layout.fragment_day, container, false);

        return view;
    }
}

fragment_day.xml

    <?xml version="1.0" encoding="utf-8"?>
<FrameLayout 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:background="@color/background_green"
    tools:context=".DayFragment">
    
    <TextView
        android:id="@+id/day"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="24dp"
        android:text="@string/day" />

</FrameLayout>

activity_day.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"
    android:background="@color/background_green"
    tools:context=".DayActivity">

    <fragment
        android:id="@+id/dayfragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">
    </fragment>


</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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/background_green"
    tools:context=".MainActivity">

<Button
    android:id="@+id/monday_btn"
    android:layout_width="140dp"
    android:layout_height="86dp"
    android:text="@string/monday"
    android:textColor="#6FED84"
    android:textSize="16sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.091"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/main_title"
    app:layout_constraintVertical_bias="0.082" />

</androidx.constraintlayout.widget.ConstraintLayout>

This is the error message I get:

2021-03-21 23:34:35.459 29479-29479/com.example.dietmanagement E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.dietmanagement, PID: 29479
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dietmanagement/com.example.dietmanagement.DayActivity}: android.view.InflateException: Binary XML file line #10: Binary XML file line #10: Error inflating class fragment
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
    at android.app.ActivityThread.-wrap11(Unknown Source:0)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
    at android.os.Handler.dispatchMessage(Handler.java:105)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6541)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
 Caused by: android.view.InflateException: Binary XML file line #10: Binary XML file line #10: Error inflating class fragment
 Caused by: android.view.InflateException: Binary XML file line #10: Error inflating class fragment
 Caused by: java.lang.NullPointerException
    at java.lang.VMClassLoader.findLoadedClass(Native Method)
    at java.lang.ClassLoader.findLoadedClass(ClassLoader.java:738)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:363)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
    at android.app.Fragment.instantiate(Fragment.java:617)
    at android.app.FragmentContainer.instantiate(FragmentContainer.java:49)
    at android.app.FragmentManagerImpl.onCreateView(FragmentManager.java:3602)
    at android.app.FragmentController.onCreateView(FragmentController.java:98)
    at android.app.Activity.onCreateView(Activity.java:6187)
    at androidx.fragment.app.FragmentActivity.onCreateView(FragmentActivity.java:338)
    at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:780)
    at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:730)
    at android.view.LayoutInflater.rInflate(LayoutInflater.java:863)
    at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:824)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
    at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
    at androidx.appcompat.app.AppCompatDelegateImpl.setContentView(AppCompatDelegateImpl.java:696)
    at androidx.appcompat.app.AppCompatActivity.setContentView(AppCompatActivity.java:170)
    at com.example.dietmanagement.DayActivity.onCreate(DayActivity.java:16)
    at android.app.Activity.performCreate(Activity.java:6975)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
    at android.app.ActivityThread.-wrap11(Unknown Source:0)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
    at android.os.Handler.dispatchMessage(Handler.java:105)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6541)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Answer 1

You're attempting to load a fragment in two different ways - directly via the layout with the <fragment> tag, which requires you to specify which Fragment you actually want to load, and as a transaction in the activity which requires a layout in which to put the fragment.

// This says - "hey Android load up a fragment for me", but you don't say which
<fragment
    android:id="@+id/dayfragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent">
</fragment>

But ...

// This says - "hey Android, shove the new "dayFragment" into the view R.id.dayFragment".
// But based on your previous XML declaration, R.id.dayFragment is itself already a
// Fragment!
FragmentTransaction fragmentTransaction;
fragmentTransaction = getSupportFragmentManager().beginTransaction();
DayFragment dayFragment = new DayFragment();
fragmentTransaction.add(R.id.dayfragment, dayFragment);
fragmentTransaction.commit();

The easiest solution for you, based on what you've posted is to replace the <fragment> element with a FragmentContainerView and either leave the code in your activity or declare the class in the xml. Please see the documentation for examples on how to do this in both ways.