TextView is set to null when I assign it a textView ID

Question

I am working on a project where I need 3 textViews to change when a button is clicked.

Here is my MainActivity class:

package davidferrara.insultgenerator;

import android.content.res.Resources;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import java.util.Random;

public class MainActivity extends AppCompatActivity {

    private boolean mHomeLayout = true;
    private Resources res;
    private TextView tvInsult1;
    private TextView tvInsult2;
    private TextView tvInsult3;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if(mHomeLayout) {
            setContentView(R.layout.home_screen);
        }
        else {
            setContentView(R.layout.insult_screen);
        }

        findViewById(R.id.generateInsultButton).setOnClickListener(btnMainButton);

        assignTextViews();

    }

    //The generate insult button
    final View.OnClickListener btnMainButton = new View.OnClickListener() {
        @Override
        public void onClick(final View v) {
            mHomeLayout = false;
            setContentView(R.layout.insult_screen);
            generateInsult();
        }
    };

    private void generateInsult(){
        res = getResources();

        String[] array1 = res.getStringArray(R.array.insults0);
        String randomStr1 = array1[new Random().nextInt(array1.length)];
        tvInsult1.setText(randomStr1);

        String[] array2 = res.getStringArray(R.array.insults1);
        String randomStr2 = array2[new Random().nextInt(array2.length)];
        tvInsult2.setText(randomStr2);

        String[] array3 = res.getStringArray(R.array.insults2);
        String randomStr3 = array3[new Random().nextInt(array3.length)];
        tvInsult3.setText(randomStr3);
    }

    private void assignTextViews(){
        tvInsult1 = findViewById(R.id.insultText1);
        tvInsult2 = findViewById(R.id.insultText2);
        tvInsult3 = findViewById(R.id.insultText3);
    }
}

In this class I have 3 textViews, tvInsult1, tvInsult2, and tvInsult3 that are declared. These are then assigned the corresponding textViews from the insult_screen using the assignTextViews method.

When the button is clicked, it sets the layout to insult_screen and the generateInsult method is called. In this method, I set the string variable randomStr1 a string from an array of strings stored in my values folder. The textView tvInsult1 then gets the text set using randomStr1, or so it should.

When I ran the program, I got this error for the line tvInsult1.setText(randomStr1);:

01-04 18:44:51.160 7699-7699/davidferrara.insultgenerator E/AndroidRuntime: FATAL EXCEPTION: main
                                                                        Process: davidferrara.insultgenerator, PID: 7699
                                                                        java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

I went back and put a break right before that line of code to debug it and it turns out that tvInsult1 was null. This is where I'm stuck. I already assigned the views using the findViewById. I've looked at multiple other issues similar to this one but none of the solutions worked for me.

Here is the other related code:

Home Screen 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"
android:layout_gravity="center">

<TextView
    android:id="@+id/textView4"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/welcome_message" />

<Button
    android:id="@+id/generateInsultButton"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/generate_button" />

</LinearLayout>

Insult Screen XML:

<?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="davidferrara.insultgenerator.MainActivity">

<TextView
    android:id="@+id/insultText1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:visibility="visible" />

<TextView
    android:id="@+id/insultText2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:visibility="visible" />

<TextView
    android:id="@+id/insultText3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:visibility="visible" />

<Button
    android:id="@+id/generateInsultButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/generate_button" />

</LinearLayout>

Here is a picture of the debugger saying that the array isn't empty and that the randomStr1 has a value assigned to it from the array:

Answer 1

The problem is with the layout XMLs you are using. You are trying to use a textview named insultText1 with your home_screen layout XML loaded, and it doesn't have that TV, only insult_layout has it (you invoked home_screen by mHomeLayout = true).