动画第四步->ValueAnimator：ofObject()

极客学院Animation教程讲解的很详细，点击进入哦

_{这里为学习的整理和补充O(∩_∩)O}

一、秒懂ofObject()概念

还记得这行代码么？

ValueAnimator valueAnimator = ValueAnimator.ofInt(0, 400);

ofInt()和 ofFloat()可以定义动画，但是这时候我想要操作其他类型肿么办？？？( ⊙ o ⊙ )这个时候，ofObject()就出场了，可以传进去任何类型的变量。
下边，一起揭开真面目~源码敬上

 /** 
@param evaluator A TypeEvaluator that will be called on each animation frame to 
* provide the ncessry interpolation between the Object values to derive the animated 
* value. 
* @param values A set of values that the animation will animate between over time. 
* @return A ValueAnimator object that is set up to animate between the given values. 
*/
public static ValueAnimator ofObject(TypeEvaluator evaluator, Object... values) {
    ValueAnimator anim = new ValueAnimator();
    anim.setObjectValues(values);
    anim.setEvaluator(evaluator);
    return anim;
}

稍微解释一下：

• evaluator: TypeEvaluator会被每个动画帧调用，根据Object... values的值和所选择的插值器，计算当前进度下所对应的值。
  其实，和Evaluator的作用是一样的~~~只是TypeEvaluator是一个自定义的 Evaluator。 ofInt要用IntEvaluator，自己设定ofObject()设置类型,自然是要自定义Evaluator的

• Object... values：指定动画变化区间，类比参考ofInt()、ofFloat()~

二、使用ofObject()

创建一个字母从 A 变化到 Z的动画
1. 自定义Evaluator

public class CharEvaluator implements TypeEvaluator {
   @Override
   public Character evaluate(float fraction, Character startValue, Character endValue) {
       int start = startValue;
       int end = endValue;
      //A(ASCII65)   Z(ASCII90)
       int curValue = (int) (startValue + (endValue - startValue) * fraction);
       return (char) curValue;
   }}

2. 开始使用

ValueAnimator valueAnimator = ValueAnimator.ofObject(new CharEvaluator(), 'A', 'X','Z');
valueAnimator.setDuration(6000);
valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
    @Override
    public void onAnimationUpdate(ValueAnimator animation) {
        char animatedValue = (char) animation.getAnimatedValue();
        view.setText(String.valueOf(animatedValue));
    }});
valueAnimator.start();

完工啦，这样就可以看到A->Z的变化哦，会发现A->X变化速度很快，X->Z变化慢哦

三、ofObject()之自定义对象示例

引用自http://wiki.jikexueyuan.com/project/android-animation/6.html

还是这个gif，咱们换种思路实现O(∩_∩)O~

1. 建立实体类

/** 
* 可以添加多种圆的属性，可以设置半径、颜色等，这里仅设置半径 
*/
public class Circle {
    //圆的半径
    private int radius;
    public Circle(int radius) {
        this.radius = radius;
    }
    public int getRadius() {
        return radius;    
} 
   public void setRadius(int radius) {
        this.radius = radius;
    }
}

2.自定义View，绘制圆形

public class MyCircleView extends View {
    private Circle curCircle;
    Paint paint = new Paint();
    public MyCircleView(Context context) {
        super(context);
    }
    public MyCircleView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    public MyCircleView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //画圆,关于绘图的知识，会在以后讲解
        if (curCircle != null) {
            paint.setColor(Color.RED);
            paint.setAntiAlias(true);
            paint.setStyle(Paint.Style.FILL);
            canvas.drawCircle(500, 600, curCircle.getRadius(), paint);
        }
    }
    //动画，这个函数是在自定义CircleEvaluator之后添加的哦
    public void doAnimate() {
        ValueAnimator valueAnimator = ValueAnimator.ofObject(new CircleEvaluator(), new Circle(20), new Circle(400));
        valueAnimator.setDuration(6000);
        valueAnimator.setInterpolator(new BounceInterpolator());
        valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                curCircle = (Circle) animation.getAnimatedValue();
                 //刷新该View
                invalidate();
            }
        });
        valueAnimator.start();
    }
}

3.xml布局中引用

4.自定义Evaluator

public class CircleEvaluator implements TypeEvaluator {
    @Override
    public Circle evaluate(float fraction, Circle startValue, Circle endValue) {
        int startValueRadius = startValue.getRadius();
        int endValueRadius = endValue.getRadius();
        int curRadius = (int) (startValueRadius + (endValueRadius - startValueRadius) * fraction);
        return new Circle(curRadius);
    }
}

5.Activity中调用一下，开始执行动画吧,至此搞定_{O(∩_∩)O}

view = (MyCircleView) findViewById(R.id.view);
view.doAnimate();