java.lang.NullPointerException in Main Activity

Question

I had a functioning program a few days ago, I switched a couple of buttons around an am now getting this error:

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.jack.synthesiser, PID: 10903
              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jack.synthesiser/com.example.jack.synthesiser.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
                  at android.app.ActivityThread.access$800(ActivityThread.java:151)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:135)
                  at android.app.ActivityThread.main(ActivityThread.java:5254)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at java.lang.reflect.Method.invoke(Method.java:372)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                  at com.example.jack.synthesiser.MainActivity.initializeView(MainActivity.java:59)
                  at com.example.jack.synthesiser.MainActivity.onCreate(MainActivity.java:38)
                  at android.app.Activity.performCreate(Activity.java:5990)
                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
                  at android.app.ActivityThread.access$800(ActivityThread.java:151) 
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                  at android.os.Looper.loop(Looper.java:135) 
                  at android.app.ActivityThread.main(ActivityThread.java:5254) 
                  at java.lang.reflect.Method.invoke(Native Method) 
                  at java.lang.reflect.Method.invoke(Method.java:372)

It's probably a simple error but cant seem to find a fix for it, any help would be much appreciated. Heres my 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:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.jack.synthesiser.MainActivity">

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:hint ="Enter frequency"
    android:inputType="textPersonName"

    android:ems="10"
    android:layout_alignParentTop="true"
    android:layout_alignParentEnd="true"
    android:layout_marginEnd="218dp"
    android:id="@+id/editText" />


<RadioGroup
android:layout_width="wrap_content"
android:layout_height="wrap_content"
    android:orientation="vertical"
    android:layout_alignParentTop="true"
    android:layout_alignParentStart="true"
    android:id="@+id/radioGroup">

    <RadioButton
        android:text="Sine"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/editText"
        android:layout_alignParentStart="true"
        android:layout_marginStart="15dp"
        android:layout_marginTop="15dp"
        android:id="@+id/radioButton" />

    <RadioButton
    android:text="Square"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/radioButton2"
    android:layout_above="@+id/toggleButton"
    android:layout_toEndOf="@+id/radioButton"
    android:layout_marginStart="15dp" />

    <RadioButton
    android:text="Saw"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/radioButton3"
    android:layout_marginStart="15dp"
    android:layout_alignBaseline="@+id/radioButton2"
    android:layout_alignBottom="@+id/radioButton2"
    android:layout_toEndOf="@+id/radioButton2" />

</RadioGroup>

<Button
    android:text="Button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/button"
    android:layout_marginStart="55dp"
    android:layout_below="@+id/radioGroup"
    android:layout_alignStart="@+id/editText"
    android:layout_marginTop="44dp" />

<SeekBar
    android:layout_width="wrap_content"
    android:layout_height="100dp"
    android:id="@+id/Volume"
    android:layout_marginStart="52dp"
    android:layout_alignParentTop="true"
    android:layout_toEndOf="@+id/button" />

<TextView
    android:text="@string/textview"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/textView"
    android:layout_alignTop="@+id/button"
    android:layout_alignStart="@+id/Volume" />

</RelativeLayout>

And this is the main activity file:

package com.example.jack.synthesiser;

import android.content.Context;
import android.media.AudioManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.SeekBar;
import android.widget.TextView;
import android.widget.ToggleButton;
import android.widget.RadioButton;


public class MainActivity extends AppCompatActivity implements      View.OnClickListener, View.OnTouchListener, SeekBar.OnSeekBarChangeListener {

EditText frequencyInput;
TextView displayFrequency;
Button startStop;
RadioButton sine;
RadioButton square;
RadioButton saw;
PlaySine sineWave = new PlaySine();
PlaySquare squareWave = new PlaySquare();
PlaySaw sawWave = new PlaySaw();
//Filter attack = new Filter();
SeekBar amplitude;
AudioManager audioManager;
float curVolume, maxVolume, volume;



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

//protected void  volumeSounds() {
//    audioManager = (AudioManager) getSystemService(AUDIO_SERVICE);
//    curVolume = (float)audioManager.getStreamVolume(AudioManager.STREAM_MUSIC);
//    maxVolume = (float)audioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC);

  //  volume = curVolume/maxVolume;
//}
private void initializeView () {

    frequencyInput = (EditText) findViewById(R.id.editText);
    startStop = (Button) findViewById(R.id.toggleButton);
    sine = (RadioButton) findViewById(R.id.radioButton);
    square = (RadioButton) findViewById(R.id.radioButton2);
    saw = (RadioButton) findViewById(R.id.radioButton3);
    //startStopSquare = (ToggleButton) findViewById(R.id.toggleButton2);
    //startStopSaw = (ToggleButton) findViewById(R.id.toggleButton3);
    displayFrequency = (TextView) findViewById(R.id.textView);
    startStop.setOnTouchListener(this);
    amplitude = (SeekBar) findViewById(R.id.Volume);
    audioManager = (AudioManager)getSystemService(Context.AUDIO_SERVICE);
    maxVolume = audioManager.getStreamMaxVolume(AudioManager.STREAM_MUSIC);
    volume = audioManager.getStreamVolume(AudioManager.STREAM_MUSIC);
    amplitude.setOnSeekBarChangeListener(this);
    //startStopSquare.setOnClickListener(this);
    //startStopSaw.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    // TODO Auto-generated method stub
    int frequency = Integer.parseInt(frequencyInput.getText().toString());
    displayFrequency.setText(String.valueOf(frequency));
    sineWave.setSine(frequency);
    squareWave.setSquareWave(frequency);
    sawWave.setSawWave(frequency);

}

@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {

}

@Override
public void onStartTrackingTouch(SeekBar seekBar) {

}

@Override
public void onStopTrackingTouch(SeekBar seekBar) {

}

@Override
public boolean onTouch(View v, MotionEvent event) {
    boolean on = ((startStop.isPressed()) && sine.isChecked());
    boolean sqOn = ((startStop.isPressed()) && square.isChecked());
    boolean sawOn =((startStop.isPressed()) && saw.isChecked());
    if (on) {
        sineWave.start();
    } else if (!on){
        sineWave.stop();
    }
    if (sqOn) {
        squareWave.start();
    } else if (!sqOn) {
        squareWave.stop();
    }
    if (sawOn) {
        sawWave.start();
    } else if (!sawOn) {
        sawWave.stop();
    }
    return false;
}
}

score 0 · Accepted Answer · answered Feb 27 '17 at 14:51

0

You are getting the error because when you try to call .setOnClickListener() on one of the buttons the variable is null. Make sure you initialized the variable first using findViewById(), for example.

answered Feb 27 '17 at 14:51

Carl Poole

1,762
2
20
28

Thanks, found the error using your advice, much appreciated – Jackington Feb 27 '17 at 15:04

java.lang.NullPointerException in Main Activity

1 Answers1