package com.example.myapplication;


import android.content.Intent;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;




public class MainActivity extends AppCompatActivity {
    public static TextView tv;
    private static Handler handler=new Handler();
    private boolean paused=false;
    Intent serviceIntent;
    public static boolean run_flag=true;
    public static int flag=1;
    public static long pre_long;

    public static int t_psec=0;
    public static int t_sec=0;
    public static int t_min=0;





    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv=(TextView)findViewById(R.id.set);
        serviceIntent=new Intent(MainActivity.this,MyService.class);
        //handler.post(background_work);
    }


    public void clear(View view)
    {
        flag=0;
        pre_long=System.currentTimeMillis();
        tv.setText("00:00:00");
        t_sec=0;
        t_psec=0;
        t_min=0;
        stopService(serviceIntent);

    }
    public void stvtc(View view){
        flag=1;
        pre_long=System.currentTimeMillis();
        startService(serviceIntent);

    }
    public void stop(View view){
        paused=true;
        flag=0;
        stopService(serviceIntent);
    }
}
 

package com.example.myapplication;


import android.app.Service;
        import android.content.Intent;
        import android.os.IBinder;


public class MyService extends Service {




    private Thread workthread;
    public MyService() {
    }

    @Override
    public void onCreate() {
        super.onCreate();
        workthread = new Thread(null,backgroundwork,"workthread");

    }

    @Override
    public void onStart(Intent intent, int startId) {
        super.onStart(intent, startId);
        if(!workthread.isAlive()){
            workthread.start();
        }
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        workthread.interrupt();
    }


    @Override
    public IBinder onBind(Intent intent) {
        return null;
        // TODO: Return the communication channel to the service.
        // throw new UnsupportedOperationException("Not yet implemented");
    }
    private Runnable backgroundwork=new Runnable() {
        @Override
        public void run() {
            try {
                while (MainActivity.run_flag)
                {
                    Thread.sleep(50);
                    if (MainActivity.flag == 1) {
                        long temp_long=System.currentTimeMillis();
                        MainActivity.t_psec = MainActivity.t_psec + (int)(temp_long/10-MainActivity.pre_long/10);
                        MainActivity.pre_long=temp_long;
                        while(MainActivity.t_psec>=100) {
                            MainActivity.t_psec=MainActivity.t_psec-100;
                            MainActivity.t_sec=MainActivity.t_sec+1;
                        }

                        while(MainActivity.t_sec>=60)
                        {        MainActivity.t_sec=MainActivity.t_sec-60;
                            MainActivity.t_min=MainActivity.t_min+1;
                        }
                        if(MainActivity.t_min==60){
                            MainActivity.t_min=0;
                        }
                        //display();
                        MainActivity.tv.post(new Runnable() {
                            @Override
                            public void run() {
                                String temp_str=String.format("%02d:%02d:%02d",MainActivity.t_min,MainActivity.t_sec,MainActivity.t_psec);
                                MainActivity.tv.setText(temp_str);
                            }
                        });
                    }
                }
            }catch (InterruptedException e){
                e.printStackTrace();
            }
        }
    };}
 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:gravity="center_horizontal">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="25dp"
            android:text="秒錶"
            android:textAlignment="center"
            android:gravity="center_horizontal"/>
        <TextView
            android:id="@+id/set"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="30dp"
            android:text="00:00:00"
            android:textAlignment="center"
            android:gravity="center_horizontal"/>
        <TextView
            android:id="@+id/hour"
            android:textSize="30dp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <TextView
            android:id="@+id/min"
            android:textSize="30dp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
        <TextView
            android:id="@+id/sec"
            android:textSize="30dp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
        <TextView
            android:orientation="horizontal"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"/>
        <Button
            android:id="@+id/start"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="開始"
            android:onClick="stvtc"
            android:textSize="20dp"
            />
        <Button
            android:id="@+id/stop"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="暫停"
            android:onClick="stop"
            android:textSize="20dp"/>
        <Button
            android:id="@+id/reset"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:onClick="clear"
            android:text="重置"
            android:textSize="20dp"/>

    </LinearLayout>
    </LinearLayout>
 

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapplication">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <service
            android:name=".MyService"/>

    </application>

</manifest>