Android自定義View實例AnalogClock源碼

針對Android底層VIEw的直接構造很多網友沒有實戰經驗，本次android開發網結合目前平台開源代碼一起通過AnalogClock類來理解VIEw的直接繼承。AnalogClock就是Home Screen上的那個帶有兩根指針的表盤類。它的實現我們直接從開源代碼可以了解到:

  public class AnalogClock extends VIEw {
    private Time mCalendar;

    private Drawable mHourHand; //時針
    private Drawable mMinuteHand; //分針
    private Drawable mDial; //表盤背景

    private int mDialWidth; //表盤寬度
    private int mDialHeight; //表盤高度

    private boolean mAttached; //附著狀態

    private final Handler mHandler = new Handler(); //定一個Handler類實現更新時間
    private float mMinutes;
    private float mHour;
    private boolean mChanged; //時間是否改變

    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); //加載表盤資源
        if (mDial == null) {
            mDial = r.getDrawable(com.android.internal.R.drawable.clock_dial);
        }

        mHourHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_hour); //加載時針圖片資源
        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); //加載分針圖片
        if (mMinuteHand == null) {
            mMinuteHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_minute);
        }

        mCalendar = new Time(); //獲取當前系統時間

        mDialWidth = mDial.getIntrinsicWidth(); //獲取表盤圖片的寬度
        mDialHeight = mDial.getIntrinsicHeight(); //高度，同上
    }

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

        if (!mAttached) {
            mAttached = true;
            IntentFilter filter = new IntentFilter(); //注冊一個消息過濾器，獲取時間改變、時區改變的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); //反注冊消息過濾器
            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;
    }

    主要的繪圖重寫VIEw的onDraw方法，我們可以看到通過canvas實例直接屏幕

@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); //計算時針旋轉的角度，android123提示就是那個時針圖片的旋轉角度，直接反應的就是表盤上那個針的時間
        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，分針旋轉的角度

        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() {  //獲取時間改變，計算當前的時分秒
        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() { //監聽獲取時間改變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(); //獲取新的時間
            
            invalidate(); //刷新屏幕，強制類調用onDraw方法實現分針時針的走動
        }
    }; 

  看了本例根據，Android開發很簡單吧，感興趣的網友可以為本程序加入一個秒針，不過android123提醒網友的是可能對於電池，以及系統運行效率產生一定的影響，不過作為練習大家可以試一試。