Android 获取控件滑动速度，速度跟踪器VelocityTracker；

VelocityTracker 速度跟踪器

在写关于Android滑动的控件，如果用户手指在屏幕上（当前位置 - 起始位置 > 某个数值）就做一个界面切换，但是总感觉太生硬，只有满足上面的条件才会触发切换界面，不管用户滑动的速度有多么的快，都要去算当前位置和起始位置的距离；但是ViewPager这个控件如果你滑动速度很快的话，就触发切换页面的效果了，怎么实现的呢；于是我去看了一下Google的ViewPager的源码，发现了这么个神器的东西：VelocityTracker；

以下是Viewpager的源码：

 @Overridepublic boolean onTouchEvent(MotionEvent ev) {if (mFakeDragging) {// A fake drag is in progress already, ignore this real one// but still eat the touch events.// (It is likely that the user is multi-touching the screen.)return true;}if (ev.getAction() == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0) {// Don't handle edge touches immediately -- they may actually belong to one of our// descendants.return false;}if (mAdapter == null || mAdapter.getCount() == 0) {// Nothing to present or scroll; nothing to touch.return false;}if (mVelocityTracker == null) {mVelocityTracker = VelocityTracker.obtain();}mVelocityTracker.addMovement(ev);final int action = ev.getAction();boolean needsInvalidate = false;switch (action & MotionEvent.ACTION_MASK) {case MotionEvent.ACTION_DOWN: {mScroller.abortAnimation();mPopulatePending = false;populate();// Remember where the motion event startedmLastMotionX = mInitialMotionX = ev.getX();mLastMotionY = mInitialMotionY = ev.getY();mActivePointerId = ev.getPointerId(0);break;}case MotionEvent.ACTION_MOVE:if (!mIsBeingDragged) {final int pointerIndex = ev.findPointerIndex(mActivePointerId);if (pointerIndex == -1) {// A child has consumed some touch events and put us into an inconsistent// state.needsInvalidate = resetTouch();break;}final float x = ev.getX(pointerIndex);final float xDiff = Math.abs(x - mLastMotionX);final float y = ev.getY(pointerIndex);final float yDiff = Math.abs(y - mLastMotionY);if (DEBUG) {Log.v(TAG, "Moved x to " + x + "," + y + " diff=" + xDiff + "," + yDiff);}if (xDiff > mTouchSlop && xDiff > yDiff) {if (DEBUG) Log.v(TAG, "Starting drag!");mIsBeingDragged = true;requestParentDisallowInterceptTouchEvent(true);mLastMotionX = x - mInitialMotionX > 0 ? mInitialMotionX + mTouchSlop :mInitialMotionX - mTouchSlop;mLastMotionY = y;setScrollState(SCROLL_STATE_DRAGGING);setScrollingCacheEnabled(true);// Disallow Parent Intercept, just in caseViewParent parent = getParent();if (parent != null) {parent.requestDisallowInterceptTouchEvent(true);}}}// Not else! Note that mIsBeingDragged can be set above.if (mIsBeingDragged) {// Scroll to follow the motion eventfinal int activePointerIndex = ev.findPointerIndex(mActivePointerId);final float x = ev.getX(activePointerIndex);needsInvalidate |= performDrag(x);}break;case MotionEvent.ACTION_UP:if (mIsBeingDragged) {final VelocityTracker velocityTracker = mVelocityTracker;velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);int initialVelocity = (int) velocityTracker.getXVelocity(mActivePointerId);mPopulatePending = true;final int width = getClientWidth();final int scrollX = getScrollX();final ItemInfo ii = infoForCurrentScrollPosition();final float marginOffset = (float) mPageMargin / width;final int currentPage = ii.position;final float pageOffset = (((float) scrollX / width) - ii.offset)/ (ii.widthFactor + marginOffset);final int activePointerIndex = ev.findPointerIndex(mActivePointerId);final float x = ev.getX(activePointerIndex);final int totalDelta = (int) (x - mInitialMotionX);int nextPage = determineTargetPage(currentPage, pageOffset, initialVelocity,totalDelta);setCurrentItemInternal(nextPage, true, true, initialVelocity);needsInvalidate = resetTouch();}break;case MotionEvent.ACTION_CANCEL:if (mIsBeingDragged) {scrollToItem(mCurItem, true, 0, false);needsInvalidate = resetTouch();}break;case MotionEvent.ACTION_POINTER_DOWN: {final int index = ev.getActionIndex();final float x = ev.getX(index);mLastMotionX = x;mActivePointerId = ev.getPointerId(index);break;}case MotionEvent.ACTION_POINTER_UP:onSecondaryPointerUp(ev);mLastMotionX = ev.getX(ev.findPointerIndex(mActivePointerId));break;}if (needsInvalidate) {ViewCompat.postInvalidateOnAnimation(this);}return true;}

有这么几行代码：
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);

final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
int initialVelocity = (int) velocityTracker.getXVelocity(mActivePointerId);

它在Touch中实例化VelocityTracker ，在UP触摸事件中获取到当前的速度；

可以仿着写个自定义的View：

public class ContinueSlideScrollView extends NestedScrollView {private final String TAG = "CCB";public ContinueSlideScrollView(Context context) {super(context);this.context = context;}public ContinueSlideScrollView(Context context, AttributeSet attrs) {super(context, attrs);this.context = context;}public ContinueSlideScrollView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);this.context = context;}@Overridepublic boolean onTouchEvent(MotionEvent ev) {if (mVelocityTracker == null) {mVelocityTracker = VelocityTracker.obtain();}mVelocityTracker.addMovement(ev);switch (ev.getAction()){case MotionEvent.ACTION_DOWN:break;case MotionEvent.ACTION_MOVE:break;case MotionEvent.ACTION_UP:final VelocityTracker velocityTracker = mVelocityTracker;velocityTracker.computeCurrentVelocity(1000, ViewConfiguration.get(context).getScaledMaximumFlingVelocity());int initialVelocity = (int) velocityTracker.getYVelocity();Log.i(TAG, initialVelocity>0 ? "向下滑动，速度是："+initialVelocity : "向上滑动，速度是："+initialVelocity);break;}return super.onTouchEvent(ev);}@Overrideprotected void onDetachedFromWindow() {mVelocityTracker.recycle();super.onDetachedFromWindow();}
}

获取到当前View的滑动速度后，你就可以对它胡作非为了！！！

Android 获取控件滑动速度，速度跟踪器VelocityTracker；相关推荐

android 获取控件在屏幕中的坐标
今天,简单讲讲android如何获取控件在屏幕中的坐标. 这个其实也很简单,但是昨天做一个功能时,需要功能控件的坐标做一些逻辑操作时,居然不知道怎么做.所以在网上查找了资料后,解决了这个问题.这里记录 ...
android获取控件宽和高
Android获取控件宽高在项目中用到了测量控件的宽和高,这个在Activity的onCreate去使用控件的getHeight()和getWidth()方法去获取是会失败的,返回的都是0.这是由于 ...
android 获取控件高度_安卓开发入门教程UI控件_ImageView
什么是ImageView ImageView是用于显示图片的UI控件. 基础样例 1.展示本地图片效果图代码 <ImageViewandroid:layout_width="wra ...
android 获取控件高度_安卓开发入门教程UI控件_ProgressBar
什么是ProgressBar ProgressBar是用于提示用户进行等待的UI控件,. 基础样例 1.loading图效果图代码布局文件代码 <ProgressBarandroid:id ...
android 获取控件 id 工具,如何使用appium desktop 获取Android APP 控件的id
背景: 随着Android 版本的更新,你会发现我们之前用的最新的版本的Appium 1.5.3无法启动我们的 Android APP 在模拟器为7.0的设备上,所以我们有必要了解如何使用 appiu ...
android获取控件的id（标识符）-根据控件id获取对应的值或控件名字-动态获取R.string的值
更多其他页面-自定义View-实用功能合集:点击查看项目中需要动态获取资源R.string的值,记录一下解决方案. demo链接: link. 直接先上个示例,下面再有详细解说: @Override ...
android获取控件宽度高度
前几天,在自定义控件的时候碰到个问题,就是在如何获取自定义控件的高宽.在自定义控件类的构造函数中,本来以为可以轻松获取,但事实不是这样.我测试了下面代码: 先是布局代码: <com.lml.ge ...
android ListView控件滑动时出现黑色背景问题解法方案
设置ListView属性android:cacheColorHint="#00000000" <ListViewandroid:id="@+id/orderDeta ...
Android图表控件MPAndroidChart实现左右滑动以及联动
前言 MPAndroidChart是一个功能强大的Android图表控件库,它实现了许多常见的图表效果.关于MPAndroidChart的使用文章已经很多了,这里不再详细介绍它的使用.当数据量过多时, ...

Android 获取控件滑动速度，速度跟踪器VelocityTracker；

VelocityTracker 速度跟踪器

Android 获取控件滑动速度，速度跟踪器VelocityTracker；相关推荐

最新文章

热门文章