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：
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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
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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
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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。
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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
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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
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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
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