Android-全局变量java.lang.NullPointerException

Question

I have 2 methods which use same 2 buttons + 1 TextView. Something like this:

public void startChange(View v) {
    final Button start = (Button) findViewById(R.id.start);
    final Button restart = (Button) findViewById(R.id.restart);
    final TextView check = (TextView) findViewById(R.id.check);
    //TO-DO part - Sets check to something based on buttons TagID
}

public void restartChange (View v) {
    final Button start = (Button) findViewById(R.id.start);
    final Button restart = (Button) findViewById(R.id.restart);
    final TextView check = (TextView) findViewById(R.id.check);
    //TO-DO part - Restars everything to basic position
}

everything worked fine.. But as soon as I made this buttons and textview global variable I got java.lang.NullPointerException. Any idea how to fix it?

Edit: Problem solved. Only think you have to do is to define buttons and textview in onCreate method not in global definition..

Example:

public class Example extends Activity {
    Button start;
    Button restart;
    TextView t;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        start = (Button) findViewById(R.id.start);
        restart = (Button) findViewById(R.id.restart);
       check = (TextView) findViewById(R.id.check);
    }
}

Answer 1

You must add setContentView(R.layout.main);

public class Example extends Activity
{
    Button start;
    Button restart;
    TextView t;

    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        start = (Button) findViewById(R.id.start);
        restart = (Button) findViewById(R.id.restart);
        check = (TextView) findViewById(R.id.check);
    }
}

Answer 2

Problem solved. Only think you have to do is to define buttons and textview in onCreate method not in global definition..

Example:

public class Example extends Activity {
    Button start;
    Button restart;
    TextView t;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        start = (Button) findViewById(R.id.start);
        restart = (Button) findViewById(R.id.restart);
       check = (TextView) findViewById(R.id.check);
    }
}