<Chronometer
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:format="%s"
android:id="@+id/timer"/>

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
timer = (Chronometer) findViewById(R.id.timer);
}
public void btnClick(View view) {
timer.setBase(SystemClock.elapsedRealtime());//计时器清零
timer.start();
}

public void btnClick(View view) {
timer.setBase(SystemClock.elapsedRealtime());//计时器清零
int hour = (int) ((SystemClock.elapsedRealtime() - timer.getBase()) / 1000 / 60);
timer.setFormat("0"+String.valueOf(hour)+":%s");
timer.start();
}
public void stopClick(View view) {
timer.stop();
}

<Chronometer
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:format="00:00:00"
android:gravity="center"
android:id="@+id/timer"/>

package com.example.nanchen.timerdemo;
import android.os.SystemClock;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Chronometer;
import android.widget.TextView;
import java.util.Locale;
import java.util.Timer;
import java.util.TimerTask;
public class MainActivity extends AppCompatActivity {
private Chronometer timer;
private Timer timer1;
private TextView textView;
private TimerTask timerTask;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
timer = (Chronometer) findViewById(R.id.timer);
textView = (TextView) findViewById(R.id.text);
timer1 = new Timer();
}
public void btnClick(View view) {
timer.setBase(SystemClock.elapsedRealtime());//计时器清零
int hour = (int) ((SystemClock.elapsedRealtime() - timer.getBase()) / 1000 / 60);
timer.setFormat("0"+String.valueOf(hour)+":%s");
timer.start();
}
public void stopClick(View view) {
timer.stop();
}
public void startClick(View view) {
timerTask = new TimerTask() {
int cnt = 0;
@Override
public void run() {
runOnUiThread(new Runnable() {
@Override
public void run() {
textView.setText(getStringTime(cnt++));
}
});
}
};
timer1.schedule(timerTask,0,1000);
}
private String getStringTime(int cnt) {
int hour = cnt/3600;
int min = cnt % 3600 / 60;
int second = cnt % 60;
return String.format(Locale.CHINA,"d:d:d",hour,min,second);
}
public void stopClick1(View view) {
if (!timerTask.cancel()){
timerTask.cancel();
timer1.cancel();
}
}
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.example.nanchen.timerdemo.MainActivity">
<Chronometer
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:format="00:00:00"
android:gravity="center"
android:id="@+id/timer"/>
<Button
android:layout_width="match_parent"
android:onClick="btnClick"
android:text="start"
android:layout_height="wrap_content"/>
<Button
android:layout_width="match_parent"
android:text="stop"
android:onClick="stopClick"
android:layout_height="wrap_content"/>
<View
android:layout_width="match_parent"
android:layout_height="1dp"
android:background="#959393"
android:layout_marginBottom="20dp"
android:layout_marginTop="20dp"/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="00:00:00"
android:gravity="center"
android:id="@+id/text"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="开始"
android:onClick="startClick"/>
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="停止"
android:onClick="stopClick1"/>
</LinearLayout>