一、前言：
我之前很早的时候，写过一篇《左右滑出菜单》的文章：
用的是对View的LeftMargin / RightMargin进行不断的计算，并且用AsynTask来完成动画，性能不是很好，大家也在资源下载中有评论，因此，本篇文件，将会采用ViewGroup的方式来自定义控件，且支持文章标题中的两种滑动方式的展现，也希望大家多多评论。（可惜，大家都去下载资源，在资源中评论了！呜呜~~）。
二、实现：
2.1 核心程序及知识点：
本次，采用ViewGroup来管理整个的Child，并且采用scrollTo / scrollBy，以及 Scroller 这么个系统方法来完成这些事。先来上主要代码：
package com.chris.apps.uiscroll;import com.chris.apps.uiscroll.R;import android.content.Context;import android.content.res.TypedArray;import android.util.AttributeSet;import android.util.Log;import android.view.MotionEvent;import android.view.VelocityTracker;import android.view.View;import android.view.ViewConfiguration;import android.view.ViewGroup;import android.widget.Scroller;public class UIScrollLayout extends ViewGroup { private final static String TAG = "UIScrollLayout"; private int mCurScreen = 0; private final static String ATTR_NAVIGATOR = "navigator"; private final static String ATTR_SLIDEMENU = "slidemenu"; public final static int VIEW_NAVIGATOR = 0; public final static int VIEW_MAIN_SLIDEMENU = 1; private int mViewType = VIEW_NAVIGATOR; private int mTouchSlop = 0; private int mLastX = 0; private VelocityTracker mVelocityTracker = null; private final static int VELOCITY_X_DISTANCE = 1000; private Scroller mScroller = null; public UIScrollLayout(Context context) { this(context, null); } public UIScrollLayout(Context context, AttributeSet attrs) { this(context, attrs, 0); } public UIScrollLayout(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.UIScroll); String type = a.getString(R.styleable.UIScroll_view_type); a.recycle(); Log.d(TAG, "type = " + type); if(type.equals(ATTR_NAVIGATOR)){ mViewType = VIEW_NAVIGATOR; }else if(type.equals(ATTR_SLIDEMENU)){ mViewType = VIEW_MAIN_SLIDEMENU; } mScroller = new Scroller(context); mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop(); Log.d(TAG, "mTouchSlop = " + mTouchSlop); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); if(mViewType == VIEW_NAVIGATOR){ for(int i = 0; i < getChildCount(); i ++){ getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec); } }else if(mViewType == VIEW_MAIN_SLIDEMENU){ for(int i = 0; i < getChildCount(); i ++){ View child = getChildAt(i); LayoutParams lp = child.getLayoutParams(); int widthSpec = 0; if(lp.width > 0){ widthSpec = MeasureSpec.makeMeasureSpec(lp.width, MeasureSpec.EXACTLY); }else{ widthSpec = widthMeasureSpec; } child.measure(widthSpec, heightMeasureSpec); } } } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { if(changed){ int n = getChildCount(); View child = null; int childLeft = 0; mCurScreen = 0; for(int i = 0; i < n; i ++){ child = getChildAt(i); child.layout(childLeft, 0, childLeft + child.getMeasuredWidth(), child.getMeasuredHeight()); childLeft += child.getMeasuredWidth(); } if(mViewType == VIEW_MAIN_SLIDEMENU){ if(n > 3){ Log.d(TAG, "error: Main SlideMenu num must <= 3"); return; } if(getChildAt(0).getMeasuredWidth() < getMeasuredWidth()){ mCurScreen = 1; scrollTo(getChildAt(0).getMeasuredWidth(), 0); }else{ mCurScreen = 0; } } Log.d(TAG, "mCurScreen = " + mCurScreen); } } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { switch(ev.getAction()){ case MotionEvent.ACTION_DOWN: mLastX = (int) ev.getX(); break; case MotionEvent.ACTION_MOVE: int x = (int) ev.getX(); if(Math.abs(x - mLastX) > mTouchSlop){ return true; } break; case MotionEvent.ACTION_CANCEL: case MotionEvent.ACTION_UP: // TODO: clean or reset break; } return super.onInterceptTouchEvent(ev); } /** * 使用VelocityTracker来记录每次的event， * 并在ACTION_UP时computeCurrentVelocity， * 得出X,Y轴方向上的移动速率 * velocityX > 0 向右移动, velocityX < 0 向左移动 */ @Override public boolean onTouchEvent(MotionEvent event) { if(mVelocityTracker == null){ mVelocityTracker = VelocityTracker.obtain(); } mVelocityTracker.addMovement(event); switch(event.getAction()){ case MotionEvent.ACTION_DOWN: mLastX = (int) event.getX(); break; case MotionEvent.ACTION_MOVE: int deltaX = mLastX - (int)event.getX(); // delta > 0向右滚动 mLastX = (int) event.getX(); scrollChild(deltaX, 0); break; case MotionEvent.ACTION_CANCEL: case MotionEvent.ACTION_UP: mVelocityTracker.computeCurrentVelocity(VELOCITY_X_DISTANCE); int velocityX = (int) mVelocityTracker.getXVelocity(); animateChild(velocityX); if(mVelocityTracker != null){ mVelocityTracker.recycle(); mVelocityTracker = null; } break; } return true; } private void scrollChild(int distanceX, int distanceY){ int firstChildPosX = getChildAt(0).getLeft() - getScrollX(); int lastChildPosX = getChildAt(getChildCount()-1).getLeft() - getScrollX(); if(mViewType == VIEW_MAIN_SLIDEMENU){ lastChildPosX -= (getWidth() - getChildAt(getChildCount()-1).getWidth()); } if(firstChildPosX != 0 && Math.abs(firstChildPosX) < Math.abs(distanceX)){ distanceX = firstChildPosX; }else if(lastChildPosX != 0 && Math.abs(lastChildPosX) < Math.abs(distanceX)){ distanceX = lastChildPosX; } if(firstChildPosX == 0 && distanceX < 0){ return; }else if(lastChildPosX == 0 && distanceX > 0){ return; } scrollBy(distanceX, 0); } private void animateChild(int velocityX){ int width = 0; int offset = 0; if(mViewType == VIEW_NAVIGATOR){ width = getWidth(); }else if(mViewType == VIEW_MAIN_SLIDEMENU){ // 默认左右两页菜单宽度一致 width = getChildAt(0).getWidth(); } /* * velocityX > 0, 向右滚动; velocityX < 0, 向左滚动 */ if(velocityX > VELOCITY_X_DISTANCE && mCurScreen > 0){ offset = (--mCurScreen) * width - getScrollX(); }else if(velocityX < -VELOCITY_X_DISTANCE && mCurScreen < getChildCount()-1){ offset = (++mCurScreen) * width - getScrollX(); }else{ mCurScreen = (getScrollX() + width/2) / width; offset = mCurScreen * width - getScrollX(); } //Log.d(TAG, "offset = " + offset); mScroller.startScroll(getScrollX(), 0, offset, 0, Math.abs(offset)); invalidate(); } @Override public void computeScroll() { if(mScroller.computeScrollOffset()){ scrollTo(mScroller.getCurrX(), mScroller.getCurrY()); postInvalidate(); } super.computeScroll(); }} 这篇文章除了以上介绍，还用到了以下知识点：
1. VelocityTracker类来跟踪手指滑动速率；（网上有很多，使用也很简单）
2. 自定义XML属性；（可以看看这篇讲解：）
3. onIntercepterTouchEvent，事件拦截（可以参考这篇：）
2.2 代码解读：2.2.1 初始化
public UIScrollLayout(Context context) { this(context, null); } public UIScrollLayout(Context context, AttributeSet attrs) { this(context, attrs, 0); } public UIScrollLayout(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.UIScroll); String type = a.getString(R.styleable.UIScroll_view_type); a.recycle(); Log.d(TAG, "type = " + type); if(type.equals(ATTR_NAVIGATOR)){ mViewType = VIEW_NAVIGATOR; }else if(type.equals(ATTR_SLIDEMENU)){ mViewType = VIEW_MAIN_SLIDEMENU; } mScroller = new Scroller(context); mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop(); Log.d(TAG, "mTouchSlop = " + mTouchSlop); } 查找自定义属性有没有，然后设置当前使用的类型，初始化Scroller，并使用ViewConfiguration来获取系统设置（这里用来判断当Touch时，是水平滚动，还是上下滚动，若含有ListView时，需要通过onInterceptTouchEvent来判断）。
2.2.2 测量child
@Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); if(mViewType == VIEW_NAVIGATOR){ for(int i = 0; i < getChildCount(); i ++){ getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec); } }else if(mViewType == VIEW_MAIN_SLIDEMENU){ for(int i = 0; i < getChildCount(); i ++){ View child = getChildAt(i); LayoutParams lp = child.getLayoutParams(); int widthSpec = 0; if(lp.width > 0){ widthSpec = MeasureSpec.makeMeasureSpec(lp.width, MeasureSpec.EXACTLY); }else{ widthSpec = widthMeasureSpec; } child.measure(widthSpec, heightMeasureSpec); } } } 根据VIEW类型，来逐个测量child大小。
2.2.3 调整child位置：
@Override protected void onLayout(boolean changed, int l, int t, int r, int b) { if(changed){ int n = getChildCount(); View child = null; int childLeft = 0; mCurScreen = 0; for(int i = 0; i < n; i ++){ child = getChildAt(i); child.layout(childLeft, 0, childLeft + child.getMeasuredWidth(), child.getMeasuredHeight()); childLeft += child.getMeasuredWidth(); } if(mViewType == VIEW_MAIN_SLIDEMENU){ if(n > 3){ Log.d(TAG, "error: Main SlideMenu num must <= 3"); return; } if(getChildAt(0).getMeasuredWidth() < getMeasuredWidth()){ mCurScreen = 1; scrollTo(getChildAt(0).getMeasuredWidth(), 0); }else{ mCurScreen = 0; } } Log.d(TAG, "mCurScreen = " + mCurScreen); } } onMeasure和onLayout都是有ViewRoot来调用，并且是在draw之前，然后，开始显示各个child。
2.2.4 消息拦截处理：
@Override public boolean onInterceptTouchEvent(MotionEvent ev) { switch(ev.getAction()){ case MotionEvent.ACTION_DOWN: mLastX = (int) ev.getX(); break; case MotionEvent.ACTION_MOVE: int x = (int) ev.getX(); if(Math.abs(x - mLastX) > mTouchSlop){ return true; } break; case MotionEvent.ACTION_CANCEL: case MotionEvent.ACTION_UP: // TODO: clean or reset break; } return super.onInterceptTouchEvent(ev); } 当child中，有ListView, GridView或ScrollView时，DOWN/MOVE/UP等消息是不会跑到当前ViewGroup的onTouchEvent中的，只有当在onInterceptTouchEvent中返回true之后，才会收到消息，因为，需要在ACTION_DOWN时，记住X点坐标，并在ACTION_MOVE中判断是否需要拦截。
2.2.5 滚动消息处理：
/** * 使用VelocityTracker来记录每次的event， * 并在ACTION_UP时computeCurrentVelocity， * 得出X,Y轴方向上的移动速率 * velocityX > 0 向右移动, velocityX < 0 向左移动 */ @Override public boolean onTouchEvent(MotionEvent event) { if(mVelocityTracker == null){ mVelocityTracker = VelocityTracker.obtain(); } mVelocityTracker.addMovement(event); switch(event.getAction()){ case MotionEvent.ACTION_DOWN: mLastX = (int) event.getX(); break; case MotionEvent.ACTION_MOVE: int deltaX = mLastX - (int)event.getX(); // delta > 0向右滚动 mLastX = (int) event.getX(); scrollChild(deltaX, 0); break; case MotionEvent.ACTION_CANCEL: case MotionEvent.ACTION_UP: mVelocityTracker.computeCurrentVelocity(VELOCITY_X_DISTANCE); int velocityX = (int) mVelocityTracker.getXVelocity(); animateChild(velocityX); if(mVelocityTracker != null){ mVelocityTracker.recycle(); mVelocityTracker = null; } break; } return true; } 在ACTION_MOVE中，计算每次移动的距离，调用scrollChild来随手滚动：
private void scrollChild(int distanceX, int distanceY){ int firstChildPosX = getChildAt(0).getLeft() - getScrollX(); int lastChildPosX = getChildAt(getChildCount()-1).getLeft() - getScrollX(); if(mViewType == VIEW_MAIN_SLIDEMENU){ lastChildPosX -= (getWidth() - getChildAt(getChildCount()-1).getWidth()); } if(firstChildPosX != 0 && Math.abs(firstChildPosX) < Math.abs(distanceX)){ distanceX = firstChildPosX; }else if(lastChildPosX != 0 && Math.abs(lastChildPosX) < Math.abs(distanceX)){ distanceX = lastChildPosX; } if(firstChildPosX == 0 && distanceX < 0){ return; }else if(lastChildPosX == 0 && distanceX > 0){ return; } scrollBy(distanceX, 0); } 这个方法，主要是判断当然是否超过边界，若本次移动的距离超过边界，则计算滚动的距离最大不超过边界，并调用系统scrollBy方法，这个方法最终会调用scrollTo方法。
2.2.6 完成自动滚动：
private void animateChild(int velocityX){ int width = 0; int offset = 0; if(mViewType == VIEW_NAVIGATOR){ width = getWidth(); }else if(mViewType == VIEW_MAIN_SLIDEMENU){ // 默认左右两页菜单宽度一致 width = getChildAt(0).getWidth(); } /* * velocityX > 0, 向右滚动; velocityX < 0, 向左滚动 */ if(velocityX > VELOCITY_X_DISTANCE && mCurScreen > 0){ offset = (--mCurScreen) * width - getScrollX(); }else if(velocityX < -VELOCITY_X_DISTANCE && mCurScreen < getChildCount()-1){ offset = (++mCurScreen) * width - getScrollX(); }else{ mCurScreen = (getScrollX() + width/2) / width; offset = mCurScreen * width - getScrollX(); } //Log.d(TAG, "offset = " + offset); mScroller.startScroll(getScrollX(), 0, offset, 0, Math.abs(offset)); invalidate(); } 在收到ACTION_UP/ACTION_CANCEL消息后，就表明本次交互完成，判断当前界面滚动的距离，以及手势速度，然后调用Scroller.startScroll方法并最终通过invalidate来完成滚动。
光有startScroll是无法完成，还必需继承computeScroll，并不断的invalidate，直到Scroller移动到终点。
@Override public void computeScroll() { if(mScroller.computeScrollOffset()){ scrollTo(mScroller.getCurrX(), mScroller.getCurrY()); postInvalidate(); } super.computeScroll(); } 三、Demo：
例子下载地址：
通过设置view_type属性来显示不同UI。 （"navigator" 或 "slidemenu"）