Question

I am learning android so I wrote this code just to toggle phone ringer mode. The code compiles with no problem, I made entry in Android Manifest, set content view to the required Layout but I run this app, I get Force close error. Can somebody tell me why Force Close errors occur so that in future I should be to figure out the problem myself.Here is the code:

package com.umer.practice2;

import android.R.bool;
import android.app.Activity;
import android.media.AudioManager;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.ToggleButton;

public class RingerMode extends Activity implements View.OnClickListener {

ToggleButton tb;
ImageView Riv;
TextView tv;
AudioManager mRing;
boolean silent;
@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.ringermode);

    tb.setOnClickListener(this);
    InitializeShit();

    mRing=(AudioManager) getSystemService(AUDIO_SERVICE);
}

private void InitializeShit() {
    // TODO Auto-generated method stub
    tb= (ToggleButton) findViewById(R.id.ringTB);
    tv= (TextView) findViewById(R.id.ringTV);
    Riv= (ImageView) findViewById(R.id.ringIV);
}

@Override
public void onClick(View v) {
    // TODO Auto-generated method stub
    checkMode();
    if(silent)
    {
        Riv.setImageResource(R.drawable.mysplash);
    }else
        {
            Riv.setImageResource(R.drawable.myscreen);
        }
}

@Override
protected void onResume() {
    // TODO Auto-generated method stub
    super.onResume();
    checkMode();
}

private void checkMode() {
    // TODO Auto-generated method stub
    int temp = mRing.getRingerMode();
    if(temp==AudioManager.RINGER_MODE_SILENT)
    {
        tv.setText("Silent");
        Riv.setImageResource(R.drawable.mysplash);
        silent= true;
    }else
        if(temp==AudioManager.RINGER_MODE_NORMAL)
        {
            tv.setText("Normal");
            Riv.setImageResource(R.drawable.myscreen);
            silent= false;
        }
    }

Many Thanks

Answer 1

You need to take a look at the logcat to see what happens. See Logcat | Android Developers.

Find the stacktrace of the crash, which points to your problem. If you can’t figure it out yourself, please copy/paste the logcat in your question.

In this very case, you are referencing tb before initializing it:

tb.setOnClickListener(this);

At this point, tb is still null, so a NullPointerException occurs. To resolve this, change your code like this:

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.ringermode);


    InitializeShit();
    tb.setOnClickListener(this);

    mRing=(AudioManager) getSystemService(AUDIO_SERVICE);
}

Also, I recommend using Java’s conventions regarding methods and variable naming:

• Classes start with a capital: e.g. MyClass
• Variables start with a lowercase: e.g. myVariable
• Methods start with a lowercase: e.g. myMethod()

This will save you from confusion later on.