java.lang.IllegalStateException: Could not find method - Android Programming for Beginners Book ERROR

Question

I recently started learning android, working in the book 'Android Programming for Beginners'.

In chapter 4 I have written the following code:

mainActivity.java:

package com.gamecodeschool.exploringlayouts;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;

public class MainActivity extends AppCompatActivity {

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

        setContentView(R.layout.main_menu);
    }

    void loadConstraintLayout(View v){
        setContentView(R.layout.activity_main);
    }

    void loadTableLayout(View v){
        //setContentView(R.layout.my_table_layout);
    }

    void loadMenuLayout(View v){
        setContentView(R.layout.main_menu);
    }
}

main_menu.xml

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

        <TextView
            android:id="@+id/textView4"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="center_horizontal"
            android:text="Menu"
            android:textSize="50sp" />

        <EditText
            android:id="@+id/editText"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="100sp"
            android:ems="10"
            android:inputType="textMultiLine"
            android:padding="15sp"
            android:text="Select a layout type to view an example. The onClick attribute of each button will call a method which executes setContentView to load the new layout" />

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal">

                <TextView
                    android:id="@+id/textView5"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center_vertical"
                    android:layout_weight=".7"
                    android:text="Load ConstraintLayout"
                    android:textSize="20sp" />

                <Button
                    android:id="@+id/button3"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_weight=".1"
                    android:onClick="loadConstraintLayout"
                    android:text="Load" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="horizontal">

                <TextView
                    android:id="@+id/textView6"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_gravity="center_vertical"
                    android:layout_weight=".7"
                    android:text="Load TableLayout"
                    android:textSize="20sp" />

                <Button
                    android:id="@+id/button4"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_weight=".1"
                    android:onClick="loadTableLayout"
                    android:text="Load" />
        </LinearLayout>

        <RatingBar
            android:id="@+id/ratingBar2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="15sp"
            android:layout_marginTop="75sp"
            android:layout_marginRight="15sp" />

</LinearLayout>

When you run the program and click either of the buttons, the program crashes and returns the following error:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.gamecodeschool.exploringlayouts, PID: 10078
    java.lang.IllegalStateException: Could not find method loadConstraintLayout(View) in a parent or ancestor Context for android:onClick attribute defined on view class androidx.appcompat.widget.AppCompatButton with id 'button3'
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.resolveMethod(AppCompatViewInflater.java:436)
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:393)
        at android.view.View.performClick(View.java:7125)
        at android.view.View.performClickInternal(View.java:7102)
        at android.view.View.access$3500(View.java:801)
        at android.view.View$PerformClick.run(View.java:27336)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

I thought it may have been something I had done so I downloaded the code directly from the publisher and it returns the same error.

Answer 1

The method loadConstraintLayout should be public:

public void loadConstraintLayout(View v){
    setContentView(R.layout.activity_main);
}