Android 如何提前知道fling velocity的距离、时间 根据滑动距离得到velocity
为什么
现在Android提供了fling(velocity)函数，但如果需要fling(distance)，fling滑动一段距离呢？ 如果需要知道fling(velocity)花了多少毫秒呢？just do it
根据Android源代码，我们可以通过高中数学来实现这些功能。直接上代码mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();mMaximumVelocity = ViewConfiguration.get(context).getScaledMaximumFlingVelocity();mMinimumVelocity = ViewConfiguration.get(context).getScaledMinimumFlingVelocity();float ppi = context.getResources().getDisplayMetrics().density * 160.0f;mPhysicalCoeff = SensorManager.GRAVITY_EARTH // g (m/s^2)* 39.37f // inch/meter* ppi* 0.84f;// double distanceEs = getSplineFlingDistance(1000);
// Log.e("getSplineFlingDistance", "getSplineFlingDistance " + distanceEs);
// int velocityRs = getVelocityByDistance(116.64459);
// Log.e("getVelocityByDistance", "getVelocityByDistance " + velocityRs);}private static final float INFLEXION = 0.35f; // Tension lines cross at (INFLEXION, 1)// Fling frictionprivate static float mFlingFriction = ViewConfiguration.getScrollFriction();private static float mPhysicalCoeff;private static float DECELERATION_RATE = (float) (Math.log(0.78) / Math.log(0.9));private double getSplineDeceleration(int velocity) {return Math.log(INFLEXION * Math.abs(velocity) / (mFlingFriction * mPhysicalCoeff));}private static double getSplineDecelerationByDistance(double distance) {final double decelMinusOne = DECELERATION_RATE - 1.0;return decelMinusOne * (Math.log(distance / (mFlingFriction * mPhysicalCoeff))) / DECELERATION_RATE;}//通过初始速度获取最终滑动距离private double getSplineFlingDistance(int velocity) {final double l = getSplineDeceleration(velocity);final double decelMinusOne = DECELERATION_RATE - 1.0;return mFlingFriction * mPhysicalCoeff * Math.exp(DECELERATION_RATE / decelMinusOne * l);}//通过需要滑动的距离获取初始速度public static int getVelocityByDistance(double distance) {final double l = getSplineDecelerationByDistance(distance);int velocity = (int) (Math.exp(l) * mFlingFriction * mPhysicalCoeff / INFLEXION);return Math.abs(velocity);}//获取滑动的时间/* Returns the duration, expressed in milliseconds */private int getSplineFlingDuration(int velocity) {final double l = getSplineDeceleration(velocity);final double decelMinusOne = DECELERATION_RATE - 1.0;return (int) (1000.0 * Math.exp(l / decelMinusOne));}使用实例在该项目中哦 https://github.com/smallnew/PullFling
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