Scroller的使用
这是一个滑动帮助类，并不可以使View真正的滑动，而是根据时间的流逝，获取插值器中的数据，传递给我们，让我们去配合scrollTo/scrollBy去让view产生缓慢滑动，产生动画的效果，其实是和属性动画同一个原理。下面是官方文档对于这个类所给的解释：
This class encapsulates scrolling. You can use scrollers (Scroller or OverScroller) to collect the data you need to produce a scrolling animation—for example, in response to a fling gesture. Scrollers track scroll offsets for you over time, but they don’t automatically apply those positions to your view. It’s your responsibility to get and apply new coordinates at a rate that will make the scrolling animation look smooth.
首先，我们要先获得这个对象，我们一起看看它的构造方法：
public Scroller (Context context)public Scroller (Context context, Interpolator interpolator)public Scroller (Context context, Interpolator interpolator, boolean flywheel)
一共有三个构造方法，我们通常用第二个比较多，给定Scroller一个插值器，让其从这种插值器中取值。那么，如何使用Scroller呢，只需调用下面的代码即可：
Scroller.(int startX, int startY, int dx, int dy, int duration)；invalidate();
就可以为Scroller指定从起始位置和结束位置以及滑动的时间，Scroller就可以帮助我们获取某一时刻，我们的view所在的位置了。接着我们需要在view的computeScroll()的方法中判断scroller是否结束，如果没有结束就用scrollTo方法使view处于正确的位置即可。
@Override public void computeScroll() { //判断是否还在滚动，还在滚动为true if (mScroller.computeScrollOffset()) { scrollTo(mScroller.getCurrX(), mScroller.getCurrY()); //更新界面 postInvalidate(); isMove = true; } super.computeScroll(); } 怎么样，用起来是不是很简单粗暴。
Scroller的源码分析
只是会使用可不行，我们不仅要知其然还要知其所以然，接下来，我们从源码的角度来分析下Scroller的工作原理。从哪里分析呢，其实也不用从Scroller类的第一行代码开始看，捡重要的看就行了。首先看看startScroll()这个方法吧：
public void startScroll(int startX, int startY, int dx, int dy, int duration) { mMode = SCROLL_MODE; mFinished = false; mDuration = duration; mStartTime = AnimationUtils.currentAnimationTimeMillis(); mStartX = startX; mStartY = startY; mFinalX = startX + dx; mFinalY = startY + dy; mDeltaX = dx; mDeltaY = dy; mDurationReciprocal = 1.0f / (float) mDuration; } 我们可以从中看到，Scroller只是给他的成员变量一一赋值而已，比如模式啊，位置信息，时间等，并没有做关于view滑动的任何工作。我们接下来调用了View的invalidate()方法，让View树重新绘制，让它绘制什么呢？什么东西都没有，这不是坑我们么？其实，View的draw方法中都会调用我们上面说的computeScroll() 方法，但是这个方法在View中却是一个空方法。接下来，我们就继续分析Scroller的computeScrollOffset()方法：
public boolean computeScrollOffset() { if (mFinished) { return false; } int timePassed = (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime); if (timePassed < mDuration) { switch (mMode) { case SCROLL_MODE: float x = timePassed * mDurationReciprocal; if (mInterpolator == null) x = viscousFluid(x); else x = mInterpolator.getInterpolation(x); mCurrX = mStartX + Math.round(x * mDeltaX); mCurrY = mStartY + Math.round(x * mDeltaY); break; case FLING_MODE: final float t = (float) timePassed / mDuration; final int index = (int) (NB_SAMPLES * t); float distanceCoef = 1.f; float velocityCoef = 0.f; if (index < NB_SAMPLES) { final float t_inf = (float) index / NB_SAMPLES; final float t_sup = (float) (index + 1) / NB_SAMPLES; final float d_inf = SPLINE_POSITION[index]; final float d_sup = SPLINE_POSITION[index + 1]; velocityCoef = (d_sup - d_inf) / (t_sup - t_inf); distanceCoef = d_inf + (t - t_inf) * velocityCoef; } mCurrVelocity = velocityCoef * mDistance / mDuration * 1000.0f; mCurrX = mStartX + Math.round(distanceCoef * (mFinalX - mStartX)); // Pin to mMinX <= mCurrX <= mMaxX mCurrX = Math.min(mCurrX, mMaxX); mCurrX = Math.max(mCurrX, mMinX); mCurrY = mStartY + Math.round(distanceCoef * (mFinalY - mStartY)); // Pin to mMinY <= mCurrY <= mMaxY mCurrY = Math.min(mCurrY, mMaxY); mCurrY = Math.max(mCurrY, mMinY); if (mCurrX == mFinalX && mCurrY == mFinalY) { mFinished = true; } break; } } else { mCurrX = mFinalX; mCurrY = mFinalY; mFinished = true; } return true; } 从这个方法中，我们可以看出，Scroller先判断滑动有没有结束，如果没有结束就去获取View此时应该所处的位置信息。这个方法中重要的是它的返回值，如果完成了返回false,没有完成才返回true。继续接着Scroller的使用段落往下看，如果mScroller.computeScrollOffset()的返回值是true的话，也就是Scroller还没结束，我们就让我们的View滑动到这里，并刷新。值得注意的是，View中的computeScroll()方法并不是运行在主线程中的，所以我们要使postInvalidate()方法来调用重绘。接着重绘又会调用View的draw方法，draw方法又会调用computeScroll()方法，直至Scroller结束。到这里我们根据平时使用的代码的走向，了解了Scroller的大致工作流程。怎么样，是不是对Scroller的理解更深刻一些了呢？
Scroller的实例
仅仅是理解还不够啊，我们得从实际开发中使用Scroller，才能真正的会用他。接下来，我会用两个实例，来升华你对Scroller的理解。
实例一：仿微信朋友圈刷新
废话不多说，直接上代码吧！
/** * 仿微信刷新 * @author Nipuream */public class WXLayout extends LinearLayout{ private static final String TAG = "WXLayout"; private int mTouchSlop; private boolean mIsBeingDragged = false; private float mLastMotionY; private float mInitialMotionY; private float resistance = 0.6f; private Scroller mScroller; private ListView mListView; private boolean isMove = false; private int duration = 300; private ScrollRershListener l; private boolean isRersh = false; public WXLayout(Context context, AttributeSet attrs) { super(context, attrs); // TODO Auto-generated constructor stub init(context); } private void init(final Context context){ ViewConfiguration config = ViewConfiguration.get(context); mTouchSlop = config.getScaledTouchSlop(); DecelerateInterpolator interpolator = new DecelerateInterpolator(); mScroller = new Scroller(context,interpolator); post(new Runnable() { @Override public void run() { // TODO Auto-generated method stub mListView = (ListView) WXLayout.this.getChildAt(0); } }); } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { // TODO Auto-generated method stub final int action = ev.getAction(); if(action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP){ mIsBeingDragged = false; return false; } if (action != MotionEvent.ACTION_DOWN && mIsBeingDragged) { return true; } switch(action){ case MotionEvent.ACTION_DOWN:{ mLastMotionY = mInitialMotionY = ev.getY(); mIsBeingDragged = false; break; } case MotionEvent.ACTION_MOVE:{ final float y = ev.getY(), x = ev.getX(); final float diff, absDiff; diff = y - mLastMotionY; absDiff = Math.abs(diff); if(absDiff > mTouchSlop){ if(diff > 1){ if(mListView.getFirstVisiblePosition()==0){ View view = mListView.getChildAt(0); Rect rect = new Rect (); view.getLocalVisibleRect(rect); if(rect.top == 0){ mLastMotionY = y; mIsBeingDragged = true; } } } } break; } } return mIsBeingDragged; } @Override public boolean onTouchEvent(MotionEvent event) { // TODO Auto-generated method stub //如果碰触到控件的边缘，就不接受这一系列的action了 if (event.getAction() == MotionEvent.ACTION_DOWN && event.getEdgeFlags() != 0) { return false; } //如果Scroller正在滑动，就不接受这次事件了 if(isMove){ return false; } switch(event.getAction()){ case MotionEvent.ACTION_DOWN:{ mLastMotionY = mInitialMotionY = event.getY(); return true; } case MotionEvent.ACTION_MOVE:{ if (mIsBeingDragged) { if(l!=null && !isRersh){ l.startRersh(); isRersh = true; } mLastMotionY = event.getY(); float moveY = mLastMotionY - mInitialMotionY; pullEvent(moveY); return true; } break; } case MotionEvent.ACTION_CANCEL: case MotionEvent.ACTION_UP:{ if(mIsBeingDragged){ mIsBeingDragged = false; startMoveAnim(getScrollY(), Math.abs(getScrollY()), duration); if(l!= null && isRersh && (event.getY() - mInitialMotionY) > 0){ l.endRersh(event.getY() - mInitialMotionY); isRersh = false; } return true; } break; } } return super.onTouchEvent(event); } private void pullEvent(float moveY){ if(l != null){ l.Rersh(moveY); } if(moveY > 0){ int value = (int) Math.abs(moveY); scrollTo(0, - (int)(value*resistance)); } } public void startMoveAnim(int startY, int dy, int duration) { isMove = true; mScroller.startScroll(0, startY, 0, dy, duration); invalidate();//通知UI线程的更新 } @Override public void computeScroll() { //判断是否还在滚动，还在滚动为true if (mScroller.computeScrollOffset()) { scrollTo(mScroller.getCurrX(), mScroller.getCurrY()); //更新界面 postInvalidate(); isMove = true; } else { isMove = false; } super.computeScroll(); } public interface ScrollRershListener{ void Rersh(float value); void startRersh(); void endRersh(float value); } public static int dip2px(Context context, float dpValue) { final float scale = context.getResources().getDisplayMetrics().density; return (int) (dpValue * scale + 0.5f); } public void setOnScrollRershListener(ScrollRershListener l){ this.l = l; }} 实例二：仿QQ侧滑删除
得多谢的博客，让我有了清晰的思路，对他的代码加以改造，从而完成了这个实例。
/** * 仿QQ侧滑删除 * @author Nipuream * */public class SlideListView extends ListView implements OnTouchListener,OnClickListener{ private static final String TAG = "SlideListView"; private Context mContext; private Scroller mScroller; /** * 初始值 */ private float initalXvalue,mLastXvalue; private float initalYvalue,mLastYvalue; /** * 确认滑动的最小速度 */ private int MIN_VELOCITY = 800; /** * 速度跟踪器 */ private VelocityTracker velocityTracker; /** * 正在被拖动的view */ private View dragView; /** * 正在被拖动的position */ private int touchPos; /** * 默认的最小滑动距离 */ private int mTouchSlop; /** * 滑动时间 */ private int DURATION_TIME = 300; /** * 出现删除按钮的Item */ private View tempView ; /** * 出现删除按钮的position */ private int tempPos ; /** * 删除按钮 */ private Button deleteBtn; /** * 移除接口 */ private RemoveItemListener l; /** * 是否可以滑动 */ private boolean isSlide = false; public SlideListView(Context context, AttributeSet attrs) { super(context, attrs); // TODO Auto-generated constructor stub init(context); } private void init(Context context){ mContext = context; AccelerateInterpolator interpolator = new AccelerateInterpolator(); mScroller = new Scroller(context,interpolator); velocityTracker = VelocityTracker.obtain(); ViewConfiguration config = ViewConfiguration.get(context); mTouchSlop = config.getScaledTouchSlop(); setOnTouchListener(this); } /** * 捕捉用户到底拖动了哪个view * 拦截事件 */ @Override public boolean dispatchTouchEvent(MotionEvent ev) { // TODO Auto-generated method stub final int action = ev.getAction(); if (action == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0) { return false; } if(action == MotionEvent.ACTION_DOWN){ mLastYvalue = initalYvalue = ev.getY(); initalXvalue = mLastXvalue = ev.getX(); if(!mScroller.isFinished()){ return super.dispatchTouchEvent(ev); } touchPos = pointToPosition((int)mLastXvalue, (int)mLastYvalue); if(touchPos == AdapterView.INVALID_POSITION){ return super.dispatchTouchEvent(ev); } GetTracker(ev); dragView = getChildAt(touchPos - getFirstVisiblePosition()); isSlide = false; }else if(action == MotionEvent.ACTION_MOVE){ mLastXvalue = ev.getX(); mLastYvalue = ev.getY(); if(velocityTracker == null){ GetTracker(ev); } velocityTracker.computeCurrentVelocity(1000); if(Math.abs(velocityTracker.getXVelocity()) > MIN_VELOCITY ||Math.abs(mLastXvalue - initalXvalue)> mTouchSlop && Math.abs(mLastYvalue - initalYvalue) < mTouchSlop){ isSlide = true; } }else if(action == MotionEvent.ACTION_UP){ CloseTracker(); } return super.dispatchTouchEvent(ev); } /** * 消费事件 */ @Override public boolean onTouchEvent(MotionEvent ev) { // TODO Auto-generated method stub if(isSlide){ switch(ev.getAction()){ case MotionEvent.ACTION_MOVE: { mLastXvalue = ev.getX(); final float moveX = mLastXvalue - initalXvalue; if(Math.abs(moveX) > dip2px(mContext, 20)) { if(moveX < 0 && Math.abs(moveX) dip2px(mContext, 50) ){ //滑动到底 if(dragView != null){ mScroller.startScroll(dragView.getScrollX(), 0, (dip2px(mContext, 100) - Math.abs(dragView.getScrollX())), 0,DURATION_TIME); invalidate(); tempView = dragView; tempPos = touchPos; setListener(); } } } } break; } } return super.onTouchEvent(ev); } private void GetTracker(MotionEvent ev){ if(velocityTracker == null){ velocityTracker = VelocityTracker.obtain(); } velocityTracker.addMovement(ev); } private void CloseTracker() { if(velocityTracker != null){ velocityTracker.recycle(); velocityTracker.clear(); velocityTracker = null; } } private void setListener(){ deleteBtn = (Button) tempView.findViewById(R.id.delete); deleteBtn.setOnClickListener(this); } @Override public void computeScroll() { // TODO Auto-generated method stub if(mScroller.computeScrollOffset()){ dragView.scrollTo(mScroller.getCurrX(), mScroller.getCurrY()); postInvalidate(); } super.computeScroll(); } public static int dip2px(Context context, float dpValue) { final float scale = context.getResources().getDisplayMetrics().density; return (int) (dpValue * scale + 0.5f); } @Override public boolean onTouch(View v, MotionEvent event) { // TODO Auto-generated method stub if(tempView != null){ dragView = tempView ; mScroller.startScroll(dragView.getScrollX(), 0, - dragView.getScrollX(), 0,DURATION_TIME); invalidate(); deleteBtn.setOnClickListener(null); deleteBtn = null; tempView = null; return true; } return false; } @Override public void onClick(View v) { // TODO Auto-generated method stub if(l != null){ l.remove(tempPos); dragView = tempView; dragView.scrollTo(0, 0); tempView = null; invalidate(); } } public interface RemoveItemListener{ void remove(int pos); } public void setOnRemoveItemListener(RemoveItemListener l){ this.l = l; }} 我觉得这两个例子都很简单，所以没有什么好解释的，我在下面也会给出下载的地址。如果有什么疑惑的，或者什么地方需要改进的请联系我QQ：571829491。 源码下载