Android 利用三阶贝塞尔曲线绘制运动轨迹的示例

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:id="@+id/rl_root"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context="stone.wshh.com.touch.MainActivity">
  <stone.wshh.com.touch.MyLoveLayout
    android:layout_marginBottom="100dp"
    android:layout_marginRight="15dp"
    android:id="@+id/love_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
  </stone.wshh.com.touch.MyLoveLayout>
  <Button
    android:id="@+id/bt_bottom"
    android:text="begin"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:layout_marginBottom="20dp"
    android:layout_width="100dp"
    android:layout_height="50dp" />
</RelativeLayout>

public class MainActivity extends Activity implements View.OnClickListener{
  private Button btBottom;
//  private WaitNoticeDialog dialog;
//  public Handler handler;
  private MyLoveLayout love;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    btBottom = (Button) findViewById(R.id.bt_bottom);
    love = (MyLoveLayout) findViewById(R.id.love_layout);
    btBottom.setOnClickListener(this);
//    handler=new IHandler(this);
//    dialog = new WaitNoticeDialog(this);
  }

  static class IHandler extends Handler {
    private WeakReference<MainActivity> ui;
    IHandler(MainActivity ui) {
      this.ui = new WeakReference<MainActivity>(ui);
    }
    @Override
    public void handleMessage(Message msg) {
      if(ui!=null&&ui.get()!=null){
        ui.get().handleMsg(msg);
      }
    }
  }

  /**
   * 线程消息处理
   * @param msg
   */
  public void handleMsg(Message msg){
    switch (msg.what) {
    }
  }

  @Override
  public void onClick(View v) {
    switch (v.getId()){
      case R.id.bt_bottom:
        love.addHeart();
        break;
    }
  }

  @Override
  protected void onDestroy() {
    super.onDestroy();
//    handler.removeCallbacksAndMessages(null);
  }
}

public class MyLoveLayout extends RelativeLayout {
  private Drawable[] drawables;
  private Interpolator[] mInterpolators;
  private int dWidth, mWidth;
  private int dHeight, mHeight;
  private LayoutParams lp;
  private Random random = new Random();

  public MyLoveLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
    //imageView位置是相对于MyLoveLayout
    init();
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    //得到本布局的宽高
    mWidth = getMeasuredWidth();
    mHeight = getMeasuredHeight();
  }

  private void init() {

    // 初始化显示的图片
    drawables = new Drawable[7];
    drawables[0] = getResources().getDrawable(R.drawable.heart_1);
    drawables[1] = getResources().getDrawable(R.drawable.heart_2);
    drawables[2] = getResources().getDrawable(R.drawable.heart_3);
    drawables[3] = getResources().getDrawable(R.drawable.heart_4);
    drawables[4] = getResources().getDrawable(R.drawable.heart_5);
    drawables[5] = getResources().getDrawable(R.drawable.heart_6);
    drawables[6] = getResources().getDrawable(R.drawable.heart_7);

    // 初始化插补器
    mInterpolators = new Interpolator[4];
    mInterpolators[0] = new LinearInterpolator();// 线性
    mInterpolators[1] = new AccelerateInterpolator();// 加速
    mInterpolators[2] = new DecelerateInterpolator();// 减速
    mInterpolators[3] = new AccelerateDecelerateInterpolator();// 先加速后减速

    // 获取图片宽高
//    dWidth = drawables[0].getIntrinsicWidth();
//    dHeight = drawables[0].getIntrinsicHeight();
    //手动设置宽高
    dWidth = dip2px(getContext(), 40);
    dHeight = dip2px(getContext(), 40);
    lp = new LayoutParams(dWidth, dHeight);
    //设置view控件的起始位置
//    lp.addRule(CENTER_HORIZONTAL, TRUE);// 这里的TRUE 要注意 不是true
    lp.addRule(ALIGN_PARENT_RIGHT, TRUE);
    lp.addRule(ALIGN_PARENT_BOTTOM, TRUE);

  }

  /**
   * dp转px值
   */
  private int dip2px(Context context, float dpValue) {
    float scale = context.getResources().getDisplayMetrics().density;
    return (int) (dpValue * scale + 0.5f);
  }

  /**
   * 进场动画，三种同时播放
   * alpha透明度 （80%-0%）
   * scaleX 宽度 target（20%-100%）
   * scaleY 高度
   * @param target
   * @return
   */
  private AnimatorSet getEnterAnimator(final View target) {
    ObjectAnimator alpha = ObjectAnimator.ofFloat(target, View.ALPHA, 0.2f, 1f);
    ObjectAnimator scaleX = ObjectAnimator.ofFloat(target, View.SCALE_X, 0.2f, 1f);
    ObjectAnimator scaleY = ObjectAnimator.ofFloat(target, View.SCALE_Y, 0.2f, 1f);
    AnimatorSet enter = new AnimatorSet();
    enter.setTarget(target);
    enter.setInterpolator(new LinearInterpolator());
    enter.setDuration(500).playTogether(alpha, scaleX, scaleY);
    return enter;
  }

  private ValueAnimator getBezierValueAnimator(final View target) {
    // 初始化贝塞尔估值器
    //随机产生两个点，以确定一条3阶贝塞尔曲线
    BezierEvaluator evaluator = new BezierEvaluator(getPointF(2), getPointF(1));
    // 起点在底部中心位置，终点在底部随机一个位置，改变new PointF()中值来改变起始位置
//    ValueAnimator animator = ValueAnimator.ofObject(evaluator, new PointF((mWidth - dWidth) /
//        2, mHeight - dHeight), new PointF(random.nextInt(getWidth()), 0));
    // 起点在右下角位置，终点在左上角位置
    ValueAnimator animator = ValueAnimator.ofObject(evaluator, new PointF(mWidth - dWidth, mHeight - dHeight), new PointF(0, 0));
    animator.setTarget(target);
    animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
      @Override
      public void onAnimationUpdate(ValueAnimator valueAnimator) {
        // 这里获取到贝塞尔曲线计算出来的的x y值 赋值给view 这样就能让爱心随着曲线走啦
        PointF pointF = (PointF) valueAnimator.getAnimatedValue();
        target.setX(pointF.x);
        target.setY(pointF.y);
        // alpha动画，根据运动距离改变透明度
//        target.setAlpha(1 - valueAnimator.getAnimatedFraction());
        target.setAlpha(1 - valueAnimator.getAnimatedFraction() + 0.3f);
      }
    });

    animator.setDuration(3000);
    return animator;
  }

  private PointF getPointF(int i) {
    PointF pointF = new PointF();
    //pointF.x,pointF.y都是随机，因此可以产生n多种轨迹
    pointF.x = random.nextInt(mWidth);//0~loveLayout.Width

    //为了美观,建议尽量保证P2在P1上面,那怎么做呢??
    //只需要将该布局的高度分为上下两部分,让p1只能在下面部分范围内变化(1/2height~height),让p2只能在上面部分范围内变化(0~1/2height),因为坐标系是倒着的;

    //0~loveLayout.Height/2
    if (i == 1) {
      pointF.y = random.nextInt(mHeight / 2) + mHeight / 2;//P1点Y轴坐标变化
    } else if (i == 2) {//P2点Y轴坐标变化
      pointF.y = random.nextInt(mHeight / 2);
    }
//    写死的一条轨迹
//    if (i == 1) {
//      pointF.x=mWidth-dWidth*2;
//      pointF.y = 3*dHeight;
//    } else if (i == 2) {
//      pointF.x=dWidth*2;
//      pointF.y = mHeight -dHeight;
//    }

    return pointF;
  }

  public void addHeart() {

    final ImageView imageView = new ImageView(getContext());
    // 随机选一个爱心
    imageView.setImageDrawable(drawables[random.nextInt(6)]);
    imageView.setLayoutParams(lp);
    addView(imageView);

    AnimatorSet finalSet = new AnimatorSet();

    AnimatorSet enterAnimatorSet = getEnterAnimator(imageView);//入场动画
    ValueAnimator bezierValueAnimator = getBezierValueAnimator(imageView);//贝塞尔曲线路径动画

    finalSet.playSequentially(enterAnimatorSet, bezierValueAnimator);
//    finalSet.playSequentially(bezierValueAnimator);
    finalSet.setInterpolator(mInterpolators[random.nextInt(4)]);
    finalSet.setTarget(imageView);

    finalSet.addListener(new AnimatorListenerAdapter() {
      @Override
      public void onAnimationEnd(Animator animation) {
        super.onAnimationEnd(animation);
        removeView((imageView));//删除爱心
      }
    });
    finalSet.start();

  }
}

public class BezierEvaluator implements TypeEvaluator<PointF> {
  private PointF mControlP1;
  private PointF mControlP2;
  public BezierEvaluator(PointF controlP1, PointF controlP2) {
    this.mControlP1 = controlP1;
    this.mControlP2 = controlP2;
  }

  @Override
  public PointF evaluate(float time, PointF start, PointF end) {

    float timeLeft = 1.0f - time;
    PointF point = new PointF();

    point.x = timeLeft * timeLeft * timeLeft * (start.x) + 3 * timeLeft * timeLeft * time *
        (mControlP1.x) + 3 * timeLeft * time *
        time * (mControlP2.x) + time * time * time * (end.x);

    point.y = timeLeft * timeLeft * timeLeft * (start.y) + 3 * timeLeft * timeLeft * time *
        (mControlP1.y) + 3 * timeLeft * time *
        time * (mControlP2.y) + time * time * time * (end.y);
    return point;
  }
}