Android threading

I have an application that consists of a group of stop watches.

I have everything working except for the background thread updating each count

If I use

public void updateAllTimers(View view) {
        _groupTimerWorker = new GroupTimerWorker(_displayLines);
        _groupTimerWorker.run();

    }

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It crashes


If I use

public void updateAllTimers(View view) {
        _groupTimerWorker = new GroupTimerWorker(_displayLines);
      new Thread (_groupTimerWorker).start();
    }

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it runs but does not update

If I do the update manually

public void updateAllTimers(View view) {
        for (int i = 0; i < _displayLines.size(); i++) {
            TimerLine tl = _displayLines.get(i);
            if (tl._isRunning) {
                tl.SetCurrentDuration();
            }
        }
    }

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It updates fine each time

I want to be able to start and pause the updates. Does anyone know the correct syntax I should use?

Other code

package com.example.redkatipo.myfirstapp;

import java.util.List;

/**
 * Created by Brian on 6/04/2015.
 */


class GroupTimerWorker implements Runnable {
    Boolean _stopping = false;
    Boolean _stopped = false;
    Boolean _paused = false;
    List<TimerLine> _lines;

    public GroupTimerWorker(List<TimerLine> lines) {
        _lines = lines;
    }

    public void Stop() {
        _stopping = true;
    }

    public void SetPaused(Boolean pause) {
        _paused = pause;
    }


    @Override
    public void run() {
        while (!_stopping) {
            try {

                Thread.sleep(1000);

                if (!_paused) {
                    updateAllTimers();
                }

            } catch (InterruptedException e) {

                e.printStackTrace();
            }
        }
    }




    public void updateAllTimers() {

        for (int i = 0; i < _lines.size(); i++) {
            TimerLine tl = _lines.get(i);
            if (tl._isRunning) {
                tl.SetCurrentDuration();
            }
        }
    }
}

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package com.example.redkatipo.myfirstapp;

import android.content.Context;
import android.os.SystemClock;
import android.content.res.Resources;
import android.text.method.BaseKeyListener;
import android.widget.TextView;
import android.widget.Button;

/**
 * Created by Brian on 27/03/2015.
 */
public class TimerLine {

    public Context _context;
    public Button _stopStart;
    TextView _person;
    public TextView _elapsed;
    boolean _isRunning;

    int _startTime = 0;
    int _currentTime = 0;
    int _previousTime = 0;

    public TimerLine(Context context, Button _control, TextView _id, TextView _output) {
        _context = context;

        _stopStart = _control;

        _person = _id;
        _elapsed = _output;
        _isRunning = false;
        _stopStart.setTag(this);

        _elapsed.setText("idle");
    }

    private int CurrentSeconds()
    {
        return (int)(SystemClock.uptimeMillis()/1000);
    }

    public void stopStartButtonClick()
    {
        if (_isRunning == false) {
            _isRunning = true;
           // _stopStart.setBackground(_context.getResources().getDrawable(R.drawable.red_button));
            _stopStart.setText("Stop");

            _elapsed.setBackground(_context.getResources().getDrawable(R.drawable.green_button));
            _previousTime = _previousTime + _currentTime - _startTime;
            _elapsed.setText(formatTime(_previousTime));

            _startTime = CurrentSeconds();
        } else {
            _isRunning = false;
           /// _stopStart.setBackground(_context.getResources().getDrawable(R.drawable.green_button));
            _stopStart.setText("Start");
            _currentTime = CurrentSeconds();
            int difference = (_currentTime - _startTime);
            int totalTime = difference + _previousTime;
            _elapsed.setText(formatTime(totalTime));
            _elapsed.setBackground(_context.getResources().getDrawable(R.drawable.red_button));

        }

    }

    public void SetCurrentDuration()
    {
        int now = CurrentSeconds();
        int difference = now - _startTime;
       int totalTime = difference + _previousTime;
        _elapsed.setText(formatTime(totalTime));
    }

    private String formatTime(int totalTime)
    {
        int minutes = totalTime/60;
        int seconds = totalTime % 60;
        return "" + minutes + ":" + String.format("%02d", seconds);
    }
}

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