Android自定义View实例AnalogClock源码

针对Android底层View的直接构造很多网友没有实战经验，本次Android开发网结合目前平台开源代码一起通过AnalogClock类来理解View的直接继承。AnalogClock就是Home Screen上的那个带有两根指针的表盘类。它的实现我们直接从开源代码可以了解到:

  public class AnalogClock extends View {
    private Time mCalendar;

    private Drawable mHourHand; //时针
    private Drawable mMinuteHand; //分针
    private Drawable mDial; //表盘背景

    private int mDialWidth; //表盘宽度
    private int mDialHeight; //表盘高度

    private boolean mAttached; //附着状态

    private final Handler mHandler = new Handler(); //定一个Handler类实现更新时间
    private float mMinutes;
    private float mHour;
    private boolean mChanged; //时间是否改变

    public AnalogClock(Context context) {
        this(context, null);
    }

    public AnalogClock(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public AnalogClock(Context context, AttributeSet attrs,
                       int defStyle) {
        super(context, attrs, defStyle);
        Resources r = mContext.getResources();
        TypedArray a =
                context.obtainStyledAttributes(
                        attrs, com.android.internal.R.styleable.AnalogClock, defStyle, 0);

        mDial = a.getDrawable(com.android.internal.R.styleable.AnalogClock_dial); //加载表盘资源
        if (mDial == null) {
            mDial = r.getDrawable(com.android.internal.R.drawable.clock_dial);
        }

        mHourHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_hour); //加载时针图片资源
        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); //加载分针图片
        if (mMinuteHand == null) {
            mMinuteHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_minute);
        }

        mCalendar = new Time(); //获取当前系统时间

        mDialWidth = mDial.getIntrinsicWidth(); //获取表盘图片的宽度
        mDialHeight = mDial.getIntrinsicHeight(); //高度，同上
    }

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

        if (!mAttached) {
            mAttached = true;
            IntentFilter filter = new IntentFilter(); //注册一个消息过滤器，获取时间改变、时区改变的action

            filter.addAction(Intent.ACTION_TIME_TICK);
            filter.addAction(Intent.ACTION_TIME_CHANGED);
            filter.addAction(Intent.ACTION_TIMEZONE_CHANGED);

            getContext().registerReceiver(mIntentReceiver, filter, null, mHandler);
        }

          mCalendar = new Time();

        onTimeChanged();
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        if (mAttached) {
            getContext().unregisterReceiver(mIntentReceiver); //反注册消息过滤器
            mAttached = false;
        }
    }

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

        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthSize =  MeasureSpec.getSize(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightSize =  MeasureSpec.getSize(heightMeasureSpec);

        float hScale = 1.0f;
        float vScale = 1.0f;

        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);

        setMeasuredDimension(resolveSize((int) (mDialWidth * scale), widthMeasureSpec),
                resolveSize((int) (mDialHeight * scale), heightMeasureSpec));
    }

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

    主要的绘图重写View的onDraw方法，我们可以看到通过canvas实例直接屏幕

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

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

        int availableWidth = mRight - mLeft;
        int availableHeight = mBottom - mTop;

        int x = availableWidth / 2;
        int y = availableHeight / 2;

        final Drawable dial = mDial;
        int w = dial.getIntrinsicWidth();
        int h = dial.getIntrinsicHeight();

        boolean scaled = false;

        if (availableWidth < w || availableHeight < h) {
            scaled = true;
            float scale = Math.min((float) availableWidth / (float) w,
                                   (float) availableHeight / (float) h);
            canvas.save();
            canvas.scale(scale, scale, x, y);
        }

        if (changed) {
            dial.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));
        }
        dial.draw(canvas);

        canvas.save();
        canvas.rotate(mHour / 12.0f * 360.0f, x, y); //计算时针旋转的角度，android123提示就是那个时针图片的旋转角度，直接反应的就是表盘上那个针的时间
        final Drawable hourHand = mHourHand;
        if (changed) {
            w = hourHand.getIntrinsicWidth();
            h = hourHand.getIntrinsicHeight();
            hourHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));
        }
        hourHand.draw(canvas);
        canvas.restore();

        canvas.save();
        canvas.rotate(mMinutes / 60.0f * 360.0f, x, y); //同理，分针旋转的角度

        final Drawable minuteHand = mMinuteHand;
        if (changed) {
            w = minuteHand.getIntrinsicWidth();
            h = minuteHand.getIntrinsicHeight();
            minuteHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));
        }
        minuteHand.draw(canvas);
        canvas.restore();

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

    private void onTimeChanged() {  //获取时间改变，计算当前的时分秒
        mCalendar.setToNow();

        int hour = mCalendar.hour;
        int minute = mCalendar.minute;
        int second = mCalendar.second;

        mMinutes = minute + second / 60.0f;
        mHour = hour + mMinutes / 60.0f;
        mChanged = true;
    }

    private final BroadcastReceiver mIntentReceiver = new BroadcastReceiver() { //监听获取时间改变action
        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(Intent.ACTION_TIMEZONE_CHANGED)) {
                String tz = intent.getStringExtra("time-zone");
                mCalendar = new Time(TimeZone.getTimeZone(tz).getID());
            }

            onTimeChanged(); //获取新的时间
            
            invalidate(); //刷新屏幕，强制类调用onDraw方法实现分针时针的走动
        }
    }; 

  看了本例根据，Android开发很简单吧，感兴趣的网友可以为本程序加入一个秒针，不过Android123提醒网友的是可能对于电池，以及系统运行效率产生一定的影响，不过作为练习大家可以试一试。