AndroidSpringAnimation弹性动画解析

dependencies {
 compile 'com.android.support:support-dynamic-animation:25.3.0'
}

SpringForce spring = new SpringForce(finalPosition);
spring.setStiffness(stiffness);
spring.setDampingRatio(dampingRatio);

SpringAnimation animation = new SpringAnimation(view, property);
animation.setSpring(spring);

public class PositionActivity extends AppCompatActivity {

 float STIFFNESS = SpringForce.STIFFNESS_MEDIUM;//硬度
 float DAMPING_RATIO = SpringForce.DAMPING_RATIO_HIGH_BOUNCY;//阻尼

 SpringAnimation xAnimation;//x方向
 SpringAnimation yAnimation;//y方向

 View movingView;//图片

 float dX = 0f;
 float dY = 0f;

 @Override
 public void onCreate(@Nullable Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_position);

  movingView = findViewById(R.id.movingView);

  // 以图片的初始位置创建动画对象
  movingView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
   @Override
   public void onGlobalLayout() {
    xAnimation = createSpringAnimation(
      movingView, SpringAnimation.X, movingView.getX(), STIFFNESS, DAMPING_RATIO);
    yAnimation = createSpringAnimation(
      movingView, SpringAnimation.Y, movingView.getY(), STIFFNESS, DAMPING_RATIO);
    //初始位置确定，移除监听
    movingView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
   }
  });

  movingView.setOnTouchListener(new View.OnTouchListener() {
   @Override
   public boolean onTouch(View view, MotionEvent event) {
    switch (event.getActionMasked()) {
     case MotionEvent.ACTION_DOWN:
      // 计算到左上角的距离
      dX = view.getX() - event.getRawX();
      dY = view.getY() - event.getRawY();

      // 取消动画以便按住图片
      xAnimation.cancel();
      yAnimation.cancel();
      break;
     case MotionEvent.ACTION_MOVE:
      // 另一种改变View的LayoutParams（位置）的方式
      movingView.animate()
        .x(event.getRawX() + dX)
        .y(event.getRawY() + dY)
        .setDuration(0)
        .start();
      break;
     case MotionEvent.ACTION_UP:
      xAnimation.start();
      yAnimation.start();
      break;
    }
    return true;
   }
  });

 }

 /**
  * 创建弹性动画
  * @param view 动画关联的控件
  * @param property 动画作用的属性
  * @param finalPosition 动画结束的位置
  * @param stiffness 硬度
  * @param dampingRatio 阻尼
  * @return
  */
 SpringAnimation createSpringAnimation(View view,
           DynamicAnimation.ViewProperty property,
           Float finalPosition,
           @FloatRange(from = 0.0) Float stiffness,
           @FloatRange(from = 0.0) Float dampingRatio) {
  //创建弹性动画类SpringAnimation
  SpringAnimation animation = new SpringAnimation(view, property);
  //SpringForce类，定义弹性特质
  SpringForce spring = new SpringForce(finalPosition);
  spring.setStiffness(stiffness);
  spring.setDampingRatio(dampingRatio);
  //关联弹性特质
  animation.setSpring(spring);
  return animation;
 }

}

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