Android实现多个倒计时优化与源码分析

因为之前有个项目需求是需要时时刻去更新UI倒计时,之前想到的,这简单嘛,用计时或者Handler就可以搞定,而且性能也不错,但是需求要ListView,什么,?大量的View都需要,那Handle处理不好会挂的啊,那轮训呢,?太消耗内存和Cpu,突然之前只有想到用Handle去处理,但是Item太多如何管理呢.?带着这样的问题,思考着纠结着,今天无意中看到一个源码还不错,

这个类是Google原生提供的数字时钟,可以实现时时刻刻的更新,我想里面肯定封装了一些实现的逻辑就跟着开始研究学习,下面是该类的主要结构:

/**
 * Like AnalogClock, but digital.  Shows seconds.
 *
 * FIXME: implement separate views for hours/minutes/seconds, so
 * proportional fonts don't shake rendering
 */

public class DigitalClock extends TextView {

    Calendar mCalendar;
    private final static String m12 = "h:mm:ss aa";
    private final static String m24 = "k:mm:ss";
    private FormatChangeObserver mFormatChangeObserver;

    private Runnable mTicker;
    private Handler mHandler;

    private boolean mTickerStopped = false;

    String mFormat;

    public DigitalClock(Context context) {
        super(context);
        initClock(context);
    }

    public DigitalClock(Context context, AttributeSet attrs) {
        super(context, attrs);
        initClock(context);
    }

    private void initClock(Context context) {
        Resources r = mContext.getResources();

        if (mCalendar == null) {
            mCalendar = Calendar.getInstance();
        }

        mFormatChangeObserver = new FormatChangeObserver(); //格式观察者,开始第一眼我看到这儿以为是通过观察者去实现的,结果只是一个格式的观察.
        getContext().getContentResolver().registerContentObserver( //注册
                Settings.System.CONTENT_URI, true, mFormatChangeObserver);

        setFormat(); // 设置格式
    }

/**
 *这个方法就是更新的核心,该方法是能正常的call onDraw或者onMeasure后便会回调.
 *
 */
 @Override
    protected void onAttachedToWindow() {
        mTickerStopped = false;
        super.onAttachedToWindow();
        mHandler = new Handler(); // 用于Post一个runable.

        /**
         * requests a tick on the next hard-second boundary
         */
        mTicker = new Runnable() {
                public void run() {
                    if (mTickerStopped) return;
                    mCalendar.setTimeInMillis(System.currentTimeMillis()); // 之前创建日历对象获取时间.
                    setText(DateFormat.format(mFormat, mCalendar)); // 设置时间
                    invalidate(); // 更新UI
                    long now = SystemClock.uptimeMillis();
                    long next = now + (1000 - now % 1000);// 这儿算法不错,保证一秒更新一次,
                    mHandler.postAtTime(mTicker, next);
                }
            };
        mTicker.run();
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        mTickerStopped = true;// 保证复用的时候,runable被系统回收.
    }

    /**
     * Pulls 12/24 mode from system settings
     */
    private boolean get24HourMode() {
        return android.text.format.DateFormat.is24HourFormat(getContext());
    }

    private void setFormat() {
        if (get24HourMode()) {
            mFormat = m24;
        } else {
            mFormat = m12;
        }
    }

    private class FormatChangeObserver extends ContentObserver {
        public FormatChangeObserver() {
            super(new Handler());
        }

        @Override
        public void onChange(boolean selfChange) {
            setFormat();
        }
    }

    @Override
    public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
        super.onInitializeAccessibilityEvent(event);
        event.setClassName(DigitalClock.class.getName());
    }

    @Override
    public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
        super.onInitializeAccessibilityNodeInfo(info);
        info.setClassName(DigitalClock.class.getName());
    }
}

看到OnAttachedToWindow方法后,可以借鉴出来一个自定义的好的写法.我就不用Calender去获取时间更新,把它封装出来给用户使用.我就暂时只贴出核心代码吧

@Override
	protected void onAttachedToWindow() {
		mTickerStopped = false;
		super.onAttachedToWindow();
		mHandler = new Handler();

		/**
		 * requests a tick on the next hard-second boundary
		 */
		mTicker = new Runnable() {
			public void run() {
				if (mTickerStopped)
					return;
				long currentTime = System.currentTimeMillis();
				if (currentTime / 1000 == endTime / 1000 - 1 * 60) { // 判定是否到了指定时间
					mClockListener.remainOneMinutes(); // 指定时间的CallBack
				}
				long distanceTime = endTime - currentTime;// 计算差值
				distanceTime /= 1000; // 转为秒
				if (distanceTime == 0) {
					setText("00:00:00");
					onDetachedFromWindow(); // 保证该runnable不在被继续运行.
					mClockListener.timeEnd(); // 结束call back.
				} else if (distanceTime < 0) {
					setText("00:00:00");
				} else {
					setText(dealTime(distanceTime));
				}
				invalidate();
				long now = SystemClock.uptimeMillis();
				long next = now + (1000 - now % 1000);// 够不够一秒,保证一秒更新一次
				mHandler.postAtTime(mTicker, next);
			}
		};
		mTicker.run();
	}

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