Question

I made a simple application that adds 1 to the count and displays the count on a TextView. It compiled and installed fine, but when I run it, a message immediately says “Unfortunately, Counter has stopped.”

package com.android.counter;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;


public class CounterActivity extends Activity {
/** Called when the activity is first created. */

private static int count = 0;
Button increment = (Button) findViewById(R.id.inc);
TextView tv = (TextView) findViewById(R.id.CountDisp);


Runnable update = new Runnable()
{
    public void run() {
        increment.setOnClickListener(new View.OnClickListener() 
        {
            public void onClick(View v) 
            {
                count++;
                tv.setText("Count:" + count);
            }
        });
    }
};


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    Thread thr = new Thread(update);
    thr.start();

}

}

Answer 1

You need to set the content of the Activity BEFORE trying to find any of the views. Doing this…

Button increment = (Button) findViewById(R.id.inc);
TextView tv = (TextView) findViewById(R.id.CountDisp);

…where you currently are, will mean both increment and tv will be null. Change those lines to…

Button increment;
TextView tv';

Then use findViewById(...) in onCreate(...) AFTER you have called setContentView(...)

Also, using a separate Thread (Runnable) to handle the onClick(...) listener is over complicating things and isn’t necessary. Simply create your onClick(...) listener within onCreate(...) and forget about the other thread code.