Android自定义View——贝塞尔曲线实现直播点赞效果

效果展示

原理分析

点赞效果最主要的难点和原理在于贝塞尔曲线动画的生成，我们通过图片主要讲解贝塞尔曲线动画

1、需要找到贝塞尔曲线的四个点
2、通过三级贝塞尔曲线的公式计算，获取贝塞尔曲线的轨迹路径点
3、通过设置点赞图片X，Y坐标，从而形成点赞的效果

实现步骤

1、初始化变量

//1、继承RelativeLayout
public class ChristmasView extends RelativeLayout implements View.OnClickListener {

    private Context context;
    //2、准备几张点赞图片
    private int[] christmas_drawable = {R.drawable.christmas01, R.drawable.christmas02, R.drawable.christmas03
            , R.drawable.christmas04, R.drawable.christmas05, R.drawable.christmas06};
    //随机数种子
    private Random random = new Random();
    //View的宽高
    private int width, height;
    //图片的宽高
    private int drawableWidth, drawableHeight;

    public ChristmasView(Context context) {
        this(context, null);
    }

    public ChristmasView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ChristmasView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        this.context = context;
        //3、设置点击事件
        setOnClickListener(this);
        //4、获取点赞图片的宽高
        Drawable drawable = ContextCompat.getDrawable(context, R.drawable.christmas01);
        drawableWidth = drawable.getIntrinsicWidth();
        drawableHeight = drawable.getIntrinsicHeight();
    }
}

@Override
public void onClick(View v) {
    //5、点击增加点赞图片
    addChristmas(context);
}

2、点赞效果的实现

private void addChristmas(Context context) {
    /**
     * 1、点击一次增加一张图片在底部
     */
    final ImageView imageView = new ImageView(context);
    imageView.setBackgroundResource(christmas_drawable[random.nextInt(christmas_drawable.length - 1)]);
    RelativeLayout.LayoutParams params = new LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
            ViewGroup.LayoutParams.WRAP_CONTENT);
    params.addRule(ALIGN_PARENT_BOTTOM);
    params.addRule(CENTER_HORIZONTAL);
    imageView.setLayoutParams(params);
    addView(imageView);

    //2、开始执行点赞效果
    AnimatorSet animatorSet = getAnimatorSet(imageView);
    animatorSet.addListener(new AnimatorListenerAdapter() {
        @Override
        public void onAnimationEnd(Animator animation) {
            //3、动画执行后移除View
            removeView(imageView);
        }
    });
    animatorSet.start();
}

3、动画实现

private AnimatorSet getAnimatorSet(ImageView imageView) {
    AnimatorSet enter = new AnimatorSet();

    //1、缩放动画
    AnimatorSet scaleAnimator = new AnimatorSet();
    ObjectAnimator alpha = ObjectAnimator.ofFloat(imageView, "alpha", 0.3f, 1f);
    ObjectAnimator scaleX = ObjectAnimator.ofFloat(imageView, "scaleX", 0.3f, 1f);
    ObjectAnimator scaleY = ObjectAnimator.ofFloat(imageView, "scaleY", 0.3f, 1f);
    scaleAnimator.setDuration(300);
    scaleAnimator.playTogether(alpha, scaleX, scaleY);

    //2、贝塞尔动画
    ValueAnimator bezierAnimator = getBezierAnimator(imageView);

    //3、两个动画按顺序播放
    enter.playSequentially(scaleAnimator, bezierAnimator);
    return enter;
}

4、贝塞尔曲线动画

它需要一个估值器，不断的计算它的运行轨迹，从起始点到终点开始计算，当中也需要中间另外的两个点进行辅助计算，这些都是由贝塞尔曲线的公式所决定的

/**
 * 贝塞尔曲线估值器：计算动画的执行轨迹
 *
 * @params 传入贝塞尔曲线需要的四个点
 * @return 通过计算返回贝塞尔曲线的坐标
 */
public class BezierEvaluator implements TypeEvaluator<PointF> {

    private PointF point1;
    private PointF point2;

    public BezierEvaluator(PointF point1, PointF point2) {
        this.point1 = point1;
        this.point2 = point2;
    }

    @Override
    public PointF evaluate(float t, PointF point0, PointF point3) {
        PointF point = new PointF();
        //t 取值为 [0,1]

        /**
         * 三阶贝塞尔公式
         *
         * B(t)=(1 - t)^3 P0
         *     + 3 t (1 - t)^2 P1
         *     + 3 t^2 (1 - t) P2
         *     + t^3 P3
         */
        point.x = point0.x * (1 - t) * (1 - t) * (1 - t)
                + 3 * point1.x * t * (1 - t) * (1 - t)
                + 3 * point2.x * t * t * (1 - t)
                + point3.x * t * t * t;

        /**
         * 三阶贝塞尔公式
         *
         * B(t)=(1 - t)^3 P0
         *     + 3 t (1 - t)^2 P1
         *     + 3 t^2 (1 - t) P2
         *     + t^3 P3
         */
        point.y = point0.y * (1 - t) * (1 - t) * (1 - t)
                + 3 * point1.y * t * (1 - t) * (1 - t)
                + 3 * point2.y * t * t * (1 - t)
                + point3.y * t * t * t;

        return point;
    }
}

在不断的计算过程中，我们就可以一直获取它的轨迹点，从而执行我们的属性动画，实现贝塞尔曲线动画

/**
 * 贝塞尔动画
 *
 * @return
 */
private ValueAnimator getBezierAnimator(final ImageView imageView) {
    //1、构建贝塞尔曲线的四个点
    PointF point0 = new PointF((width - drawableWidth) / 2, height - drawableHeight);
    PointF point1 = new PointF(random.nextInt(width), random.nextInt(height / 2));
    PointF point2 = new PointF(random.nextInt(width), random.nextInt(height / 2) + height / 2);
    PointF point3 = new PointF(random.nextInt(width - drawableWidth), 0);

    //2、创建贝塞尔属性动画
    BezierEvaluator evaluator = new BezierEvaluator(point1, point2);
    final ValueAnimator valueAnimator = ObjectAnimator.ofObject(evaluator, point0, point3);
    valueAnimator.setInterpolator(new LinearInterpolator());
    valueAnimator.setDuration(3000);
    //3、监听贝塞尔曲线估值器返回值
    valueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            //4、获取BezierEvaluator中evaluate()返回的运行轨迹坐标点，设置点赞图片路线
            PointF pointF = (PointF) animation.getAnimatedValue();
            imageView.setX(pointF.x);
            imageView.setY(pointF.y);
            //6、获取BezierEvaluator中evaluate()返回的参数t，设置消失动画
            float t = animation.getAnimatedFraction();
            imageView.setAlpha(1 - t + 0.2f);
        }
    });
    return valueAnimator;
}

5、View的使用

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.handsome.boke2.CustomView.ChristmasView
        android:layout_width="100dp"
        android:layout_height="200dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true" />
</RelativeLayout>

6、源码下载

源码下载