Android开发计时器的三种实现方式

释放双眼,带上耳机,听听看~!

 

本文实例为大家分享了Android计时器的三种方法,具体内容如下

目录:

1、借助Timer实现

2、调用handler.sendMessagedely(Message msg, long delayMillis)

3、借助布局Chronometer

1、借助Timer实现

(1) 布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/timerView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:textSize="60sp" />
</LinearLayout>

布局文件很简单,就是一个TextView用来显示计时时间。下面看一下Activity里的逻辑实现:

(2)Activity文件

public class MyChronometer extends Activity {
private TextView timerView;
private long baseTimer;
@Override
protected void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.chrono);
MyChronometer.this.baseTimer = SystemClock.elapsedRealtime();
timerView = (TextView) this.findViewById(R.id.timerView);
final Handler startTimehandler = new Handler(){
public void handleMessage(android.os.Message msg) {
if (null != timerView) {
timerView.setText((String) msg.obj);
}
}
};
new Timer("开机计时器").scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
int time = (int)((SystemClock.elapsedRealtime() - MyChronometer.this.baseTimer) / 1000);
String hh = new DecimalFormat("00").format(time / 3600);
String mm = new DecimalFormat("00").format(time % 3600 / 60);
String ss = new DecimalFormat("00").format(time % 60);
String timeFormat = new String(hh + ":" + mm + ":" + ss);
Message msg = new Message();
msg.obj = timeFormat;
startTimehandler.sendMessage(msg);
}
}, 0, 1000L);
super.onCreate(savedInstanceState);
}

新开一个定时器(Timer), 在子线程中获取开机时间并转成字符串格式, 利用handler传回UI线程显示。

(3)运行结果:

2.调用handler.sendMessagedely(Message msg, long delayMillis)

(1) 布局文件与方法1 相同,运行结果与方法1 相同

(2)Activity文件

public class MyChronometer extends Activity {
private TextView timerView;
private long baseTimer;
@Override
protected void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.chrono);
MyChronometer.this.baseTimer = SystemClock.elapsedRealtime();
timerView = (TextView) this.findViewById(R.id.timerView);
Handler myhandler = new Handler(){
public void handleMessage(android.os.Message msg) {
if (0 == MyChronometer.this.baseTimer) {
MyChronometer.this.baseTimer = SystemClock.elapsedRealtime();
}
int time = (int)((SystemClock.elapsedRealtime() - MyChronometer.this.baseTimer) / 1000);
String hh = new DecimalFormat("00").format(time / 3600);
String mm = new DecimalFormat("00").format(time % 3600 / 60);
String ss = new DecimalFormat("00").format(time % 60);
if (null != MyChronometer.this.timerView) {
timerView.setText(hh + ":" + mm + ":" + ss);
}
sendMessageDelayed(Message.obtain(this, 0x0), 1000);
}
};
myhandler.sendMessageDelayed(Message.obtain(myhandler, 0x0), 1000);
super.onCreate(savedInstanceState);
}

sendMessageDelayed (Message msg, long delayMillis):在 delayMillis/1000 秒后发送消息 msg。

在Handler 的 handleMessage()方法中调用sendMessageDelayed方法, 巧妙的实现了循环。需要注意的是,在Handler外要调用一次startTimehandler.sendMessageDelayed(Message.obtain(startTimehandler, 0x0), 1000);  以作为循环的入口。

3.借助布局Chronometer

(1) 布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<Chronometer
android:id="@+id/chronometer"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:textSize="60sp" />
</LinearLayout>

布局Chronometer继承自TextView

(2)Activity文件

public class MyChronometer extends Activity {
Chronometer chronometer;
@Override
protected void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.chrono);
chronometer = (Chronometer) this.findViewById(R.id.chronometer);
chronometer.setBase(SystemClock.elapsedRealtime());
chronometer.start();
super.onCreate(savedInstanceState);
}
}

逻辑代码很简单,调用chronometer.start()就可以开始计时。

chronometer.setBase(long base):设置起始计时点,这里设置的是获取开机时间。

chronometer.start():以上面setBase()设置的时间点为起始点,开始计时,看一下start()的源码就知道了:

public void start() {
mStarted = true;
updateRunning();
}

调用了updateRunning(), 跟入updateRunning()方法:

private void updateRunning() {
boolean running = mVisible && mStarted;
if (running != mRunning) {
if (running) {
updateText(SystemClock.elapsedRealtime());
dispatchChronometerTick();
mHandler.sendMessageDelayed(Message.obtain(mHandler, TICK_WHAT), 1000);
} else {
mHandler.removeMessages(TICK_WHAT);
}
mRunning = running;
}
}
private Handler mHandler = new Handler() {
public void handleMessage(Message m) {
if (mRunning) {
updateText(SystemClock.elapsedRealtime());
dispatchChronometerTick();
sendMessageDelayed(Message.obtain(this, TICK_WHAT), 1000);
}
}
};

用updateText()方法设置时间显示。 至于计时循环机制,和方法二相同,同样是调用了handler的handMessageDelayed方法。

(3)运行结果:

注意:最后说一个关于Chronometer类的常见问题,看到很多人都问用Chronometer类如何设置格式HH:MM:SS的时间。(如果您有此问题请继续看,没有问题请忽略)

问这个问题的童鞋先看一下官方文档的描述:

If the format string is null, or if you never call setFormat(), the Chronometer will simply display the timer value in “MM:SS” or “H:MM:SS” form.

也就是说默认情况下,使用的格式是”MM:SS” 或者 “H:MM:SS”, 然后有童鞋又会问:那到底是”MM:SS” 还是 “H:MM:SS”。我们先看一下源码:

updateText():

private synchronized void updateText(long now) {
long seconds = now - mBase;
seconds /= 1000;
String text = DateUtils.formatElapsedTime(mRecycle, seconds);
if (mFormat != null) {
Locale loc = Locale.getDefault();
if (mFormatter == null || !loc.equals(mFormatterLocale)) {
mFormatterLocale = loc;
mFormatter = new Formatter(mFormatBuilder, loc);
}
mFormatBuilder.setLength(0);
mFormatterArgs[0] = text;
try {
mFormatter.format(mFormat, mFormatterArgs);
text = mFormatBuilder.toString();
} catch (IllegalFormatException ex) {
if (!mLogged) {
Log.w(TAG, "Illegal format string: " + mFormat);
mLogged = true;
}
}
}
setText(text);
}

调用了DateUtils.formatElapsedTime, 看一下DateUtils.formatElapsedTime里面都有啥:

public static String formatElapsedTime(StringBuilder recycle, long elapsedSeconds) {
Formatter f = new Formatter(sb, Locale.getDefault());
initFormatStrings();
if (hours > 0) {
return f.format(sElapsedFormatHMMSS, hours, minutes, seconds).toString();
} else {
return f.format(sElapsedFormatMMSS, minutes, seconds).toString();
}
}

代码较多,我就挑重点截取了,仔细看看上面哪个if(){}else{}语句,你肯定就恍然大悟了吧?

为了我们理论的正确性,将方法三 Activity中的代码稍作修改:

chronometer.setBase(-18000000);

运行结果如下:

 

人已赞赏
Android文章

Android开发如何修改APK包名

2020-2-2 0:04:08

Android文章

Android开发动画简单实现

2020-2-2 1:59:20

个人中心
购物车
优惠劵
今日签到
有新私信 私信列表
搜索