Updating textView with while loop?

Question

I programmed a stopwatch but it works with java, but not on Android. If I press the Button it makes nothing. Could it be, that maybe Eclipse is wrong installed?

package com.example.stoppuhr;

import java.text.SimpleDateFormat;

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


public class MainActivity extends Activity implements OnClickListener {

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

    long start;
    long millis;

    public void onClick(View v) {
        Button start1 = (Button)findViewById(R.id.button1);
        Button button2 = (Button)findViewById(R.id.button2);
        TextView textView1 = (TextView)findViewById(R.id.textView1);
        start1.setOnClickListener(this);

I think here is the problem.

        if (v.getId() == start1.getId()){
            textView1.setText("moldu");
            start = System.currentTimeMillis();

            while (true){
                millis = System.currentTimeMillis()-start;



                SimpleDateFormat sdfDate = new SimpleDateFormat("mm:ss.SSS");//dd/MM/yyyy
                String ausgeben = sdfDate.format(millis);

                textView1.setText(ausgeben);
                try {
                    Thread.sleep(30);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }   
        }

    }

}

Thank you for your help

What did you mean by _but it works with java, but not on Android_? — M. Abbas, Aug 20 '13 at 11:55
I tried the same code with a normal java application with the difference: System.out.println and textview.setText — hobbyprogrammer, Aug 20 '13 at 11:57
You're blocking UI thread ! Read about UI thread in Android. — Mike, Aug 20 '13 at 11:57

score 3 · Answer 1 · edited May 23 '17 at 11:56

Initialize your views in onCreate

Button start1,button2
TextView textView1;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    start1 = (Button)findViewById(R.id.button1);
    button2 = (Button)findViewById(R.id.button2);
    textView1 = (TextView)findViewById(R.id.textView1);
    start1.setOnClickListener(this); 
}

You are also calling Thread.sleep(30) on the ui thread. This will block the ui thread.

http://developer.android.com/training/articles/perf-anr.html

Quoting from the docs

If you implement Thread or HandlerThread, be sure that your UI thread does not block while waiting for the worker thread to complete—do not call Thread.wait() or Thread.sleep().

Make sure you do not call Thread.sleep() on the ui thread.

I suggest you have a look at the count down timer.

public static void sleep (long time) // in milliseconds

Added in API level 1 Causes the thread which sent this message to sleep for the given interval of time (given in milliseconds). The precision is not guaranteed - the Thread may sleep more or less than requested.

Parameters time The time to sleep in milliseconds. Throws InterruptedException if interrupt() was called for this Thread while it was sleeping See Also interrupt()

score 3 · Accepted Answer · answered Aug 20 '13 at 11:59

public void onClick(View v) {

Is a method that should be called when a button is clicked, but you have to register your class an OnClickListener for your button. You try to do this inside onClick.

So your class (MainActivity) will never be registered as an OnClickListener. Try moving this:

Button start1 = (Button)findViewById(R.id.button1);
start1.setOnClickListener(this);

to onCreate.

score 0 · Answer 3 · answered Aug 20 '13 at 12:11

First thing you need to do: addOnClickListener(), you can read about it. I'd google it to understand how it works.

If you added this to your button, by using

Button buttonname = (Button) findViewById(R.id.yourbuttonid);
buttonname.setOnClickListener(this);

in your onCreate() method, you successfully added the onClickListener() to the button.
If this button is pressed now, the onClick() will be called.

Updating textView with while loop?

3 Answers3