NineOldAndroidsDemos 学习(9) CustomEvaluator

public class CustomEvaluator extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.animator_custom_evaluator);
        LinearLayout container = (LinearLayout) findViewById(R.id.container);
        final MyAnimationView animView = new MyAnimationView(this);
        container.addView(animView);

        Button starter = (Button) findViewById(R.id.startButton);
        starter.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                animView.startAnimation();
            }
        });
    }

    public class XYHolder {
        private float mX;
        private float mY;

        public XYHolder(float x, float y) {
            mX = x;
            mY = y;
        }

        public float getX() {
            return mX;
        }

        public void setX(float x) {
            mX = x;
        }

        public float getY() {
            return mY;
        }

        public void setY(float y) {
            mY = y;
        }
    }

    public class XYEvaluator implements TypeEvaluator {
        public Object evaluate(float fraction, Object startValue, Object endValue) { //你可以自己计算在某个时间点的位置
            XYHolder startXY = (XYHolder) startValue;                                //这里做的是匀速直线运动
            XYHolder endXY = (XYHolder) endValue;
            return new XYHolder(startXY.getX() + fraction * (endXY.getX() - startXY.getX()),
                    startXY.getY() + fraction * (endXY.getY() - startXY.getY()));
        }
    }

    public class BallXYHolder {

        private ShapeHolder mBall;

        public BallXYHolder(ShapeHolder ball) {
            mBall = ball;
        }

        public void setXY(XYHolder xyHolder) {
            mBall.setX(xyHolder.getX());
            mBall.setY(xyHolder.getY());
        }

        public XYHolder getXY() {
            return new XYHolder(mBall.getX(), mBall.getY());
        }
    }

    public class MyAnimationView extends View implements ValueAnimator.AnimatorUpdateListener {

        public final ArrayList<ShapeHolder> balls = new ArrayList<ShapeHolder>();
        ValueAnimator bounceAnim = null;
        ShapeHolder ball = null;
        BallXYHolder ballHolder = null;

        public MyAnimationView(Context context) {
            super(context);
            ball = createBall(25, 25);
            ballHolder = new BallXYHolder(ball);
        }

        private void createAnimation() {
            if (bounceAnim == null) {
                XYHolder startXY = new XYHolder(30f, 100f);//动画开始点
                XYHolder midXY = new XYHolder(300f, 700f); //中间点
                XYHolder endXY = new XYHolder(400f, 500f);//结束点
                // 在这里 xY对于的是 BallXYHolder 对象的getXY 和setXY ,这里有个地方需要注意get 和set 的第一个
                //字母会被转化为大写 所以xY 和XY 都可以实现 动画 但是 xy 和Xy 对应的却是   getXy 和 setXy 故不
                //能实现动画会报方法不能找到的错误.
                
                //这里的执行顺序是这样的
                //1. 读取startXY midXY endXY
                //2. 通过XYEvaluator的 evaluate 计算当前帧 的 位置
                //3. 读取 返回的XYHolder 通过 BallXYHolder 的setXY 来这是小球的位置
                bounceAnim = ObjectAnimator.ofObject(ballHolder, "xY", 
                        new XYEvaluator(), startXY, midXY ,endXY); //values参数可以随便设置几个设几个
                bounceAnim.setDuration(1500);
                bounceAnim.addUpdateListener(this);
            }
        }

        public void startAnimation() {
            createAnimation();
            bounceAnim.start();
        }

        private ShapeHolder createBall(float x, float y) {
            OvalShape circle = new OvalShape();
            circle.resize(50f, 50f);
            ShapeDrawable drawable = new ShapeDrawable(circle);
            ShapeHolder shapeHolder = new ShapeHolder(drawable);
            shapeHolder.setX(x - 25f);
            shapeHolder.setY(y - 25f);
            int red = (int)(Math.random() * 255);
            int green = (int)(Math.random() * 255);
            int blue = (int)(Math.random() * 255);
            int color = 0xff000000 | red << 16 | green << 8 | blue;
            Paint paint = drawable.getPaint(); //new Paint(Paint.ANTI_ALIAS_FLAG);
            int darkColor = 0xff000000 | red/4 << 16 | green/4 << 8 | blue/4;
            RadialGradient gradient = new RadialGradient(37.5f, 12.5f,
                    50f, color, darkColor, Shader.TileMode.CLAMP);
            paint.setShader(gradient);
            shapeHolder.setPaint(paint);
            return shapeHolder;
        }

        @Override
        protected void onDraw(Canvas canvas) {
            canvas.save();
            canvas.translate(ball.getX(), ball.getY());
            ball.getShape().draw(canvas);
            canvas.restore();
        }

        public void onAnimationUpdate(ValueAnimator animation) {
            invalidate();
        }

    }
}