Android计时器的三种实现方式(Chronometer、Timer、handler)
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:
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持我们。