InertiaTimerTask.java
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package com.contrarywind.timer;
import com.contrarywind.view.WheelView;
import java.util.TimerTask;
/**
* 滚动惯性的实现
*
* @author 小嵩
* date: 2017-12-23 23:20:44
*/
public final class InertiaTimerTask extends TimerTask {
private float mCurrentVelocityY; //当前滑动速度
private final float mFirstVelocityY;//手指离开屏幕时的初始速度
private final WheelView mWheelView;
/**
* @param wheelView 滚轮对象
* @param velocityY Y轴滑行速度
*/
public InertiaTimerTask(WheelView wheelView, float velocityY) {
super();
this.mWheelView = wheelView;
this.mFirstVelocityY = velocityY;
mCurrentVelocityY = Integer.MAX_VALUE;
}
@Override
public final void run() {
//防止闪动，对速度做一个限制。
if (mCurrentVelocityY == Integer.MAX_VALUE) {
if (Math.abs(mFirstVelocityY) > 2000F) {
mCurrentVelocityY = mFirstVelocityY > 0 ? 2000F : -2000F;
} else {
mCurrentVelocityY = mFirstVelocityY;
}
}
//发送handler消息 处理平顺停止滚动逻辑
if (Math.abs(mCurrentVelocityY) >= 0.0F && Math.abs(mCurrentVelocityY) <= 20F) {
mWheelView.cancelFuture();
mWheelView.getHandler().sendEmptyMessage(MessageHandler.WHAT_SMOOTH_SCROLL);
return;
}
int dy = (int) (mCurrentVelocityY / 100F);
mWheelView.setTotalScrollY(mWheelView.getTotalScrollY() - dy);
if (!mWheelView.isLoop()) {
float itemHeight = mWheelView.getItemHeight();
float top = (-mWheelView.getInitPosition()) * itemHeight;
float bottom = (mWheelView.getItemsCount() - 1 - mWheelView.getInitPosition()) * itemHeight;
if (mWheelView.getTotalScrollY() - itemHeight * 0.25 < top) {
top = mWheelView.getTotalScrollY() + dy;
} else if (mWheelView.getTotalScrollY() + itemHeight * 0.25 > bottom) {
bottom = mWheelView.getTotalScrollY() + dy;
}
if (mWheelView.getTotalScrollY() <= top) {
mCurrentVelocityY = 40F;
mWheelView.setTotalScrollY((int) top);
} else if (mWheelView.getTotalScrollY() >= bottom) {
mWheelView.setTotalScrollY((int) bottom);
mCurrentVelocityY = -40F;
}
}
if (mCurrentVelocityY < 0.0F) {
mCurrentVelocityY = mCurrentVelocityY + 20F;
} else {
mCurrentVelocityY = mCurrentVelocityY - 20F;
}
//刷新UI
mWheelView.getHandler().sendEmptyMessage(MessageHandler.WHAT_INVALIDATE_LOOP_VIEW);
}
}