自定义View | ofObject详解与实战（ValueAnimator进阶）

    public static ValueAnimator ofObject(TypeEvaluator evaluator, Object... values) {
        ValueAnimator anim = new ValueAnimator();
        anim.setObjectValues(values);
        anim.setEvaluator(evaluator);
        return anim;
    }

    private void startAnimationTestCharEvaluator() {
        ValueAnimator animator = ValueAnimator.ofObject(new CharEvaluator(), 'A', 'Z');

        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                char text = (Character) animation.getAnimatedValue();
                tv_text.setText(String.valueOf(text));
            }
        });
        animator.setDuration(10000);
        animator.setInterpolator(new AccelerateInterpolator());
        animator.start();
    }

public class CharEvaluator implements TypeEvaluator<Character> {

    @Override
    public Character evaluate(float fraction, Character startValue, Character endValue) {
        int startInt = (int)startValue;
        int endInt = (int)endValue;
        int curInt = (int) (startInt + fraction * (endInt - startInt));

        char result = (char) curInt;
        
        return result;
    }

}

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape='oval'>
    
    <solid android:color="#0066FF"/>
    
</shape>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".CustomViews.FallingBallActivity">

    <ImageView
        android:id="@+id/ball_img"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:src="@drawable/circle"/>

    <Button
        android:id="@+id/start_fallingBallAnim"
        android:text="StartAnim"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

public class FallingBallActivity extends AppCompatActivity {

    private Button startAnim;
    private ImageView ballImg;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_falling_ball);

        initViews();
    }

    private void initViews() {
        startAnim = findViewById(R.id.start_fallingBallAnim);
        ballImg = findViewById(R.id.ball_img);

        startAnim.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //设置自定义Evaluator， 以及初始值终止值（皆为Point类型）
                ValueAnimator animator = ValueAnimator.ofObject(new FallingBallEvaluator(),
                        new Point(0, 0), new Point(500, 500));

                animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                    @Override
                    public void onAnimationUpdate(ValueAnimator animation) {
                        Point mCurPoint = (Point) animation.getAnimatedValue();

                        //以函数x，y值为左上坐标，加以自身宽高为右下坐标
                        ballImg.layout(mCurPoint.x, mCurPoint.y, mCurPoint.x + ballImg.getWidth(),
                                mCurPoint.y + ballImg.getHeight());
                    }
                });
                animator.setDuration(2000);
                animator.start();
            }
        });
    }
}

public class FallingBallEvaluator implements TypeEvaluator<Point> {

    private Point point = new Point();

    @Override
    public Point evaluate(float fraction, Point startValue, Point endValue) {
        point.x = (int) (startValue.x + fraction * (endValue.x - startValue.x));

        //y为二倍速
        if (fraction * 2 <= 1) {

            //y二倍速，若未完成，继续二倍刷新
            point.y = (int) (startValue.y + fraction * 2 * (endValue.y - startValue.y));
        } else {
            //如果完成，则不变
            point.y = endValue.y;
        }

        return point;
    }
}