Android 使用 CountDownTimer

在onResume()方法中构造CountDownTimer的好处是，onResume()是在onRestoreInstanceState()之后执行的, 这样就可以在onRestoreInstanceState()中恢复上次倒计时后的剩余时间，这样在手机屏幕旋转后，倒计时不会重置。

MainActivity.java

package com.example.countdowntimeexample;

import android.os.Bundle;
import android.os.CountDownTimer;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.TextView;

public class MainActivity extends Activity {

	private TextView mTimeLabel;
	CountDownTimer myTimer;
	long myTime = 30000;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);

		mTimeLabel = (TextView) findViewById(R.id.text);	
	}

	@Override
	protected void onResume() {
	       
		myTimer = new CountDownTimer(myTime, 1000) {

			@Override
			public void onTick(long arg0) {
				mTimeLabel.setText("second remaining: " + arg0 / 1000);
				myTime = arg0;
			}

			@Override
			public void onFinish() {
				mTimeLabel.setText("done!");
				myTime = 0;
			}
		}.start();
		super.onResume();
	}

	@Override
	protected void onStop() {
		myTimer.cancel(); // 取消计时器 
		super.onStop();
	}

	@Override
	protected void onSaveInstanceState(Bundle outState) {
   // 保存本次倒计时余下的时间，以便在acitivity再次激活的时候能从上次的断点继续倒计时 
		outState.putLong("time", myTime); 
		super.onSaveInstanceState(outState);
	}

	@Override
	protected void onRestoreInstanceState(Bundle savedInstanceState) {
    // 恢复上次倒计时断点，onResume函数将使用这个值来构造CountDownTimer
		myTime = savedInstanceState.getLong("time");
		super.onRestoreInstanceState(savedInstanceState);
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}
}

activity_main.xml

<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</RelativeLayout>