Why does my app crash on my second activity?

Question

I am a starter in Android Studio. My first app works just fine but when I select the home button it crashes.

Here is my HomeActivity.java:::

package com.example.ir_sensor;

import androidx.appcompat.app.AppCompatActivity;

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

public class HomeActivity extends AppCompatActivity {

private Switch homeAwaySwitch;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_home);
    homeAwaySwitch = homeAwaySwitch.findViewById(R.id.Switch_HomeAway);
}

public void switchChange (View v) {
    if (homeAwaySwitch.isChecked()) {
        homeAwaySwitch.setText("Home");
    } else if (!homeAwaySwitch.isChecked()) {
        homeAwaySwitch.setText("Away");
    }
}
}

Here is my activity_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=".HomeActivity">

<ImageView
    android:id="@+id/Image_House"
    android:layout_width="72dp"
    android:layout_height="71dp"
    android:layout_marginStart="16dp"
    android:layout_marginTop="16dp"
    android:contentDescription="@string/image_view"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:srcCompat="@drawable/house_menu" />

<TextView
    android:id="@+id/textView"
    android:layout_width="77dp"
    android:layout_height="20dp"
    android:layout_marginStart="24dp"
    android:text="@string/location"
    android:textAlignment="textStart"
    android:textSize="18sp"
    app:layout_constraintBottom_toBottomOf="@+id/Image_House"
    app:layout_constraintStart_toEndOf="@+id/Image_House"
    app:layout_constraintTop_toTopOf="@+id/Image_House"
    app:layout_constraintVertical_bias="1.0" />

<Switch
    android:id="@+id/Switch_HomeAway"
    android:layout_width="250dp"
    android:layout_height="47dp"
    android:layout_marginStart="80dp"
    android:layout_marginTop="255dp"
    android:onClick="switchChange"
    android:text="Switch"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/Image_House" />

</androidx.constraintlayout.widget.ConstraintLayout>

Here is my LogCat:::

2019-08-18 19:42:54.636 15559-15559/com.example.ir_sensor E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.ir_sensor, PID: 15559 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ir_sensor/com.example.ir_sensor.HomeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.widget.Switch.findViewById(int)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) at android.os.Handler.dispatchMessage(Handler.java:107) at android.os.Looper.loop(Looper.java:214) at android.app.ActivityThread.main(ActivityThread.java:7356) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.widget.Switch.findViewById(int)' on a null object reference at com.example.ir_sensor.HomeActivity.onCreate(HomeActivity.java:17) at android.app.Activity.performCreate(Activity.java:7802) at android.app.Activity.performCreate(Activity.java:7791) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)  at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)  at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)  at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)  at android.os.Handler.dispatchMessage(Handler.java:107)  at android.os.Looper.loop(Looper.java:214)  at android.app.ActivityThread.main(ActivityThread.java:7356)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 

Can you help me?

Answer 1

Your homeAwaySwitch is to be assigned to the Switch_HomeAway ID of the context and not of the homeAwaySwitch activity.

Try this

homeAwaySwitch = findViewById(R.id.Switch_HomeAway)