属性动画高级运用

1、自定义TypeEvaluator

1、TypeEvaluator的作用

• 告诉动画系统如何从初始值过度到结束值

2、FloatEvaluator的代码实现：

• evaluate()方法当中传入了三个参数，第一个参数fraction非常重要，这个参数用于表示动画的完成度的，我们应该根据它来计算当前动画的值应该是多少，第二第三个参数分别表示动画的初始值和结束值。那么上述代码的逻辑就比较清晰了，用结束值减去初始值，算出它们之间的差值，然后乘以fraction这个系数，再加上初始值，那么就得到当前动画的值了。

  public class FloatEvaluator implements TypeEvaluator {  
    public Object evaluate(float fraction, Object startValue, Object endValue) {  
        float startFloat = ((Number) startValue).floatValue();  
        return startFloat + fraction * (((Number) endValue).floatValue() - startFloat);  
    }  
  }  
  

3、使用ValueAnimator.ofObject()时，自定义TypeEvaluator

• 先定义一个Point类

  public class Point {  
  
    private float x;  
  
    private float y;  
  
    public Point(float x, float y) {  
        this.x = x;  
        this.y = y;  
    }  
  
    public float getX() {  
        return x;  
    }  
  
    public float getY() {  
        return y;  
    }  
  
  }  
  

• 定义PointEvaluator

  public class PointEvaluator implements TypeEvaluator{  
  
    @Override  
    public Object evaluate(float fraction, Object startValue, Object endValue) {  
        Point startPoint = (Point) startValue;  
        Point endPoint = (Point) endValue;  
        float x = startPoint.getX() + fraction * (endPoint.getX() - startPoint.getX());  
        float y = startPoint.getY() + fraction * (endPoint.getY() - startPoint.getY());  
        Point point = new Point(x, y);  
        return point;  
    }  
  
  }  
  

• 自定义ColorEvaluator（ObjectAnimator必须保证作用对象有set和get）

  public class ColorEvaluator implements TypeEvaluator {  
  
        private int mCurrentRed = -1;  
  
        private int mCurrentGreen = -1;  
  
        private int mCurrentBlue = -1;  
  
        @Override  
        public Object evaluate(float fraction, Object startValue, Object endValue) {  
            String startColor = (String) startValue;  
            String endColor = (String) endValue;  
            int startRed = Integer.parseInt(startColor.substring(1, 3), 16);  
            int startGreen = Integer.parseInt(startColor.substring(3, 5), 16);  
            int startBlue = Integer.parseInt(startColor.substring(5, 7), 16);  
            int endRed = Integer.parseInt(endColor.substring(1, 3), 16);  
            int endGreen = Integer.parseInt(endColor.substring(3, 5), 16);  
            int endBlue = Integer.parseInt(endColor.substring(5, 7), 16);  
            // 初始化颜色的值  
            if (mCurrentRed == -1) {  
                mCurrentRed = startRed;  
            }  
            if (mCurrentGreen == -1) {  
                mCurrentGreen = startGreen;  
            }  
            if (mCurrentBlue == -1) {  
                mCurrentBlue = startBlue;  
            }  
            // 计算初始颜色和结束颜色之间的差值  
            int redDiff = Math.abs(startRed - endRed);  
            int greenDiff = Math.abs(startGreen - endGreen);  
            int blueDiff = Math.abs(startBlue - endBlue);  
            int colorDiff = redDiff + greenDiff + blueDiff;  
            if (mCurrentRed != endRed) {  
                mCurrentRed = getCurrentColor(startRed, endRed, colorDiff, 0,  
                fraction);  
            } else if (mCurrentGreen != endGreen) {  
                mCurrentGreen = getCurrentColor(startGreen, endGreen, colorDiff,  
                redDiff, fraction);  
            } else if (mCurrentBlue != endBlue) {  
                mCurrentBlue = getCurrentColor(startBlue, endBlue, colorDiff,  
                redDiff + greenDiff, fraction);  
            }  
            // 将计算出的当前颜色的值组装返回  
            String currentColor = "#" + getHexString(mCurrentRed)  
            + getHexString(mCurrentGreen) + getHexString(mCurrentBlue);  
            return currentColor;  
        }  
  
        /** 
         * 根据fraction值来计算当前的颜色。 
         */  
        private int getCurrentColor(int startColor, int endColor, int colorDiff,  
        int offset, float fraction) {  
            int currentColor;  
            if (startColor > endColor) {  
                currentColor = (int) (startColor - (fraction * colorDiff - offset));  
                if (currentColor < endColor) {  
                    currentColor = endColor;  
                }  
            } else {  
                currentColor = (int) (startColor + (fraction * colorDiff - offset));  
                if (currentColor > endColor) {  
                    currentColor = endColor;  
                }  
            }  
            return currentColor;  
        }  
  
        /** 
         * 将10进制颜色值转换成16进制。 
         */  
        private String getHexString(int value) {  
            String hexString = Integer.toHexString(value);  
            if (hexString.length() == 1) {  
                hexString = "0" + hexString;  
            }  
            return hexString;  
        }  
  
    }  
  

• 使用

  public class MyAnimView extends View {  
  
    public static final float RADIUS = 50f;  
  
    private Point currentPoint;  
  
    private Paint mPaint;  
  
    public MyAnimView(Context context, AttributeSet attrs) {  
        super(context, attrs);  
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);  
        mPaint.setColor(Color.BLUE);  
    }  
  
    private String color;  
  
    public String getColor() {  
        return color;  
    }  
  
    public void setColor(String color) {  
        this.color = color;  
        mPaint.setColor(Color.parseColor(color));  
        invalidate();  
    }  
  
    @Override  
    protected void onDraw(Canvas canvas) {  
        if (currentPoint == null) {  
            currentPoint = new Point(RADIUS, RADIUS);  
            drawCircle(canvas);  
            startAnimation();  
        } else {  
            drawCircle(canvas);  
        }  
    }  
  
    private void drawCircle(Canvas canvas) {  
        float x = currentPoint.getX();  
        float y = currentPoint.getY();  
        canvas.drawCircle(x, y, RADIUS, mPaint);  
    }  
  
    private void startAnimation() {  
        Point startPoint = new Point(RADIUS, RADIUS);  
        Point endPoint = new Point(getWidth() - RADIUS, getHeight() - RADIUS);  
        ValueAnimator anim = ValueAnimator.ofObject(new PointEvaluator(), startPoint, endPoint);  
        anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {  
            @Override  
            public void onAnimationUpdate(ValueAnimator animation) {  
                currentPoint = (Point) animation.getAnimatedValue();  
                invalidate();  
            }  
        });  
        ObjectAnimator anim2 = ObjectAnimator.ofObject(this, "color", new ColorEvaluator(),   
            "#0000FF", "#FF0000");  
        AnimatorSet animSet = new AnimatorSet();  
        animSet.play(anim).with(anim2);  
        animSet.setDuration(5000);  
        animSet.start();  
    }  
  
  }  
  

• 效果

  
  20150504225554203.gif

2、自定义TimeInterpolator

1、TimeInterpolator

• 它的主要作用是可以控制动画的变化速率，比如去实现一种非线性运动的动画效果。

2、 TimeInterpolator源码

• 只有一个getInterpolation()方法。大家有兴趣可以通过注释来对这个接口进行详解的了解，这里我就简单解释一下，getInterpolation()方法中接收一个input参数，这个参数的值会随着动画的运行而不断变化，不过它的变化是非常有规律的，就是根据设定的动画时长匀速增加，变化范围是0到1。也就是说当动画一开始的时候input的值是0，到动画结束的时候input的值是1，而中间的值则是随着动画运行的时长在0到1之间变化的。

• nput的值是由系统经过计算后传入到getInterpolation()方法中的，然后我们可以自己实现getInterpolation()方法中的算法，根据input的值来计算出一个返回值，而这个返回值就是fraction了。

  public interface TimeInterpolator {  
  
      float getInterpolation(float input);  
  }  
  

3、自定义DecelerateAccelerateInterpolator，实现先减速后加速的效果

• DecelerateAccelerateInterpolato

  public class DecelerateAccelerateInterpolator implements TimeInterpolator{  
  
    @Override  
    public float getInterpolation(float input) {  
        float result;  
        if (input <= 0.5) {  
            result = (float) (Math.sin(Math.PI * input)) / 2;  
        } else {  
            result = (float) (2 - Math.sin(Math.PI * input)) / 2;  
        }  
        return result;  
    }  
  
  }  
  

• 使用效果 anim.setInterpolator(new DecelerateAccelerateInterpolator());
  

  20150530230114481.gif

• 另外，系统提供了BounceInterpolator，是一种可以模拟物理规律，实现反复弹起效果的Interpolator

  
  20150530230521897.gif