Android 自定义 View 实例 AnalogClock

import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.BroadcastReceiver;
import android.content.res.Resources;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.os.Handler;
import android.text.format.DateUtils;
import android.text.format.Time;
import android.util.AttributeSet;
import android.view.View;
import android.widget.RemoteViews.RemoteView;


import java.util.TimeZone;


/**
 * This widget display an analogic clock with two hands for hours and
 * minutes.
 *
 * @attr ref android.R.styleable#AnalogClock_dial
 * @attr ref android.R.styleable#AnalogClock_hand_hour
 * @attr ref android.R.styleable#AnalogClock_hand_minute
 */
@RemoteView
public class AnalogClock extends View {
    private Time mCalendar;


    private Drawable mHourHand;//定义时针
    private Drawable mMinuteHand;//定义分针
    private Drawable mDial;//定义表盘


    private int mDialWidth;//定义表盘的宽度
    private int mDialHeight;//定义表盘的高度


    private boolean mAttached;//定义是否是附着的view


    private final Handler mHandler = new Handler();//handeler用来发送和处理消息，这里用来更新时间
    private float mMinutes;//存储分钟的时间变量
    private float mHour;//存储小时的时间变量
    private boolean mChanged;//表示时间是否发生改变

   //构造方法
    public AnalogClock(Context context) {
        this(context, null);
    }

    //构造方法
    public AnalogClock(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

//构造方法
    public AnalogClock(Context context, AttributeSet attrs,
                       int defStyle) {
        super(context, attrs, defStyle);

        Resources r = mContext.getResources();//获得当前Context中/res目录下的资源

//定义一个数组，用来存放obtainStyledAttributes(AttributeSet, int[], int, int)获得的类型值

        TypedArray a =           
                context.obtainStyledAttributes(
                        attrs, com.android.internal.R.styleable.AnalogClock, defStyle, 0);

//相当于Resource.getDrawble,从styleable中获得dial的图片资源
        mDial = a.getDrawable(com.android.internal.R.styleable.AnalogClock_dial);

        if (mDial == null) {//如果找不到图片资源，则从/res/drawble下面寻找图片资源，下同

            mDial = r.getDrawable(com.android.internal.R.drawable.clock_dial);
        }


        mHourHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_hour);
        if (mHourHand == null) {
            mHourHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_hour);
        }


        mMinuteHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_minute);
        if (mMinuteHand == null) {
            mMinuteHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_minute);
        }


        mCalendar = new Time();//初始化，获得当前的时间


        mDialWidth = mDial.getIntrinsicWidth();//获得mDial的原始宽度
        mDialHeight = mDial.getIntrinsicHeight();//获得mDial的原始高度
    }


    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();


        if (!mAttached) {//如果没有附着view

            mAttached = true;

    //声明意图（消息）过滤器,过滤类型为action，获得表针，时间，时区改变的信息

            IntentFilter filter = new IntentFilter();


            filter.addAction(Intent.ACTION_TIME_TICK);//添加一个表针移动的action
            filter.addAction(Intent.ACTION_TIME_CHANGED);//添加一个时间改变的action
            filter.addAction(Intent.ACTION_TIMEZONE_CHANGED);//添加一个时区改变action

    //注册mIntentReceiver，接受filter信息
            getContext().registerReceiver(mIntentReceiver, filter, null, mHandler);
        }


        // NOTE: It's safe to do these after registering the receiver since the receiver always runs
        // in the main thread, therefore the receiver can't run before this method returns.


        // The time zone may have changed while the receiver wasn't registered, so update the Time
        mCalendar = new Time();//当receiver未注册时，时区可能已经改变，所以要更新当前时间


        // Make sure we update to the current time
        onTimeChanged();
    }


    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        if (mAttached) {//如果有附着窗口
            getContext().unregisterReceiver(mIntentReceiver);//移除前面注册的mIntentReceiver
            mAttached = false;
        }
    }


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {


        int widthMode = MeasureSpec.getMode(widthMeasureSpec);//获得MeasureSpec（测量规范）中的width的模式
        int widthSize =  MeasureSpec.getSize(widthMeasureSpec);//获得MeasureSpec（测量规范）中的width大小
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightSize =  MeasureSpec.getSize(heightMeasureSpec);


        float hScale = 1.0f;//水平的放缩规模
        float vScale = 1.0f;//垂直方向的放缩规模

//如果widthMode不是指定的模式，并且widthSize < mDialWidth，则需要将view放缩，即扩大view尺寸
        if (widthMode != MeasureSpec.UNSPECIFIED && widthSize < mDialWidth) {
            hScale = (float) widthSize / (float) mDialWidth;
        }


        if (heightMode != MeasureSpec.UNSPECIFIED && heightSize < mDialHeight) {
            vScale = (float )heightSize / (float) mDialHeight;
        }


        float scale = Math.min(hScale, vScale);//选择最小的放缩规模

//测量图片的高度和宽度，并存储之
        setMeasuredDimension(resolveSizeAndState((int) (mDialWidth * scale), widthMeasureSpec, 0),
                resolveSizeAndState((int) (mDialHeight * scale), heightMeasureSpec, 0));
    }


    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        mChanged = true;
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);


        boolean changed = mChanged;
        if (changed) {
            mChanged = false;
        }


        int availableWidth = mRight - mLeft;//availableWidth是整个屏幕的宽度，mRight是最右边的端点值，mLeft是最右边的端点值
        int availableHeight = mBottom - mTop;//avaailableHeight是整个屏幕的高度，mBottom是屏幕最低端的端点值，mTop是最上端端点值

//(x,y)是屏幕的中心点的坐标
        int x = availableWidth / 2;
        int y = availableHeight / 2;


        final Drawable dial = mDial;
        int w = dial.getIntrinsicWidth();//获得dial的宽度
        int h = dial.getIntrinsicHeight();//获得dial的高度


        boolean scaled = false;


        if (availableWidth < w || availableHeight < h) {//如果dial的宽度和高度大于屏幕的高度和宽度，就要进行重新绘制
            scaled = true;

            float scale = Math.min((float) availableWidth / (float) w,
                                   (float) availableHeight / (float) h);//获得超出屏幕大小的比例

            canvas.save();
            canvas.scale(scale, scale, x, y);//扩大
        }


        if (changed) {//设置dial的边界，将dail放在view的正中间
            dial.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));
        }
        dial.draw(canvas);//在canvas上画出dial


        canvas.save();//dial画完之后保存
        canvas.rotate(mHour / 12.0f * 360.0f, x, y);//让时针绕点（x,y）旋转起来，mHour / 12.0f * 360.0f是时针旋转的角度
        final Drawable hourHand = mHourHand;
        if (changed) {
            w = hourHand.getIntrinsicWidth();//获得时针图片的宽度
            h = hourHand.getIntrinsicHeight();//获得时针图片的高度，下同
            hourHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));//设置时针的边界，将时针也放置在view的中间
        }
        hourHand.draw(canvas);//绘制时针
        canvas.restore();//remove all modifications to the matrix/clip state since the last save call（取消上一次的保存）


        canvas.save();//重新保存
        canvas.rotate(mMinutes / 60.0f * 360.0f, x, y);//让分针绕点(x,y)旋转，mMinutes / 60.0f * 360.0f是分针的旋转角度


        final Drawable minuteHand = mMinuteHand;
        if (changed) {
            w = minuteHand.getIntrinsicWidth();//获得分针的宽度
            h = minuteHand.getIntrinsicHeight();//获得分针的高度
            minuteHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));//设置分针的边界，将其放在view的中间位置,即dial图片的中心在点(x,y)位置
        }
        minuteHand.draw(canvas);
        canvas.restore();


        if (scaled) {
            canvas.restore();
        }
    }


    private void onTimeChanged() {
        mCalendar.setToNow();//获得当前的时间


        int hour = mCalendar.hour;//获得当前时间的小时
        int minute = mCalendar.minute;//获得当前时间的分钟
        int second = mCalendar.second;//获得当前时间的秒


        mMinutes = minute + second / 60.0f;//动态的显示没经过一秒钟时，mMinutes的值
        mHour = hour + mMinutes / 60.0f;
        mChanged = true;


        updateContentDescription(mCalendar);
    }


    private final BroadcastReceiver mIntentReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(Intent.ACTION_TIMEZONE_CHANGED)) {//如果时区发生改变，就要更新时区
                String tz = intent.getStringExtra("time-zone");
                mCalendar = new Time(TimeZone.getTimeZone(tz).getID());
            }


            onTimeChanged();
            
            invalidate();//使整个窗口客户区无效，Invalidate()之后：...OnPaint()->OnPrepareDC()->OnDraw()
        }
    };


    private void updateContentDescription(Time time) {
        final int flags = DateUtils.FORMAT_SHOW_TIME | DateUtils.FORMAT_24HOUR;
        String contentDescription = DateUtils.formatDateTime(mContext,//按照当地习俗转换日期或时间格式（MM:SS或HH:MM:SS）
                time.toMillis(false), flags);
        setContentDescription(contentDescription);
    }
}