在上一篇文章《Android自己定义组件系列【3】——自己定义ViewGroup实现側滑》中实现了仿Facebook和人人网的側滑效果，这一篇我们将接着上一篇来实现双面滑动的效果。

1、布局示意图：

2、核心代码

  @Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {super.onMeasure(widthMeasureSpec, heightMeasureSpec);mWidth = MeasureSpec.getSize(widthMeasureSpec);  //获取MyScrollView的宽度mHeight = MeasureSpec.getSize(heightMeasureSpec); //获取MyScrollView的高度if(!isLocked){initX = getScrollX();isLocked = true;}}

在该方法中获取到初始的视图坐标偏移量getScrollX()

   @Overridepublic boolean onTouchEvent(MotionEvent event) {float x = event.getX();switch (event.getAction()) {case MotionEvent.ACTION_DOWN:System.out.println("ACTION_DOWN");mDownX = x;          //记录按下时的x坐标break;case MotionEvent.ACTION_UP:System.out.println("ACTION_UP");int dis = (int) (x - mDownX);   //滑动的距离if(Math.abs(dis) > (mWidth * mMenuWeight / 2)){if(dis > 0){          //假设>0则是向右滑动toRightMove();}else{                 //假设<0则是向左滑动toLeftMove();}}break;default:break;}return true;}

监听函数记录下按下和移动的屏幕坐标。求差计算出移动距离，假设这个距离大于阀值 （mWidth * mMenuWeight / 2)则滑动

 public void toRightMove(){System.out.println("maxRight = " + maxRight);System.out.println("X = "  + getScrollX());if(getScrollX() >= initX){int dx = (int)(mWidth * mMenuWeight);mScroller.startScroll(getScrollX(), 0, -dx, 0, 500);if(mListener != null){mListener.onChanged();}invalidate();}}

假设是向右滑动则。假设当前是初始位置（centerView在中间）则能够向右滑动（getScrollX == initX），或者当前左边View能够看见，则能够向右滑动将centerView移动到中间（getScrollX > initX).同理有向左滑动的方法。

    public void toLeftMove(){System.out.println("maxLeft = " + maxLeft);System.out.println("X = "  + getScrollX());if(getScrollX() <= initX){int dx = (int)(mWidth * mMenuWeight);mScroller.startScroll(getScrollX(), 0, dx, 0, 500);if(mListener != null){mListener.onChanged();}invalidate();}}

3、所有代码

MyScrollView.java

package com.example.testscrollto;import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.Scroller;public class MyScrollView extends LinearLayout{private Context mContext;private int mWidth;private int mHeight;private float mMenuWeight = 3.0f / 5; //菜单界面比例private View mMenuView;   //菜单界面private View mPriView;   //内容界面private View mRightView;  //右边界面private int maxLeft;private int maxRight;private int initX;private boolean isLocked = false;private Scroller mScroller;private OnMenuChangedListener mListener;public MyScrollView(Context context, AttributeSet attrs) {super(context, attrs);mContext = context;mScroller = new Scroller(mContext);}@Overrideprotected void onLayout(boolean changed, int l, int t, int r, int b) {super.onLayout(changed, l, t, r, b);mMenuView.layout(-(int)(mWidth * mMenuWeight), 0, 0, mHeight);mPriView.layout(0, 0, mWidth, mHeight);mRightView.layout(mWidth, 0, mWidth + (int)(mWidth * mMenuWeight), mHeight);}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {super.onMeasure(widthMeasureSpec, heightMeasureSpec);mWidth = MeasureSpec.getSize(widthMeasureSpec);  //获取MyScrollView的宽度mHeight = MeasureSpec.getSize(heightMeasureSpec); //获取MyScrollView的高度if(!isLocked){initX = getScrollX();isLocked = true;}}/**设置右滑的菜单View*/public void setMenu(View menu){mMenuView = menu;addView(mMenuView);}/*** 设置主界面View*/public void setPrimary(View primary){mPriView = primary;addView(mPriView);}public void setRightView(View rightview){mRightView = rightview;addView(mRightView);}private float mDownX;@Overridepublic boolean onTouchEvent(MotionEvent event) {float x = event.getX();switch (event.getAction()) {case MotionEvent.ACTION_DOWN:System.out.println("ACTION_DOWN");mDownX = x;          //记录按下时的x坐标break;case MotionEvent.ACTION_UP:System.out.println("ACTION_UP");int dis = (int) (x - mDownX);   //滑动的距离if(Math.abs(dis) > (mWidth * mMenuWeight / 2)){if(dis > 0){          //假设>0则是向右滑动toRightMove();}else{                 //假设<0则是向左滑动toLeftMove();}}break;default:break;}return true;}@Overridepublic void computeScroll() {super.computeScroll();if(mScroller.computeScrollOffset()){scrollTo(mScroller.getCurrX(), mScroller.getCurrY());postInvalidate();}}public void toRightMove(){System.out.println("maxRight = " + maxRight);System.out.println("X = "  + getScrollX());if(getScrollX() >= initX){int dx = (int)(mWidth * mMenuWeight);mScroller.startScroll(getScrollX(), 0, -dx, 0, 500);if(mListener != null){mListener.onChanged();}invalidate();}}public void toLeftMove(){System.out.println("maxLeft = " + maxLeft);System.out.println("X = "  + getScrollX());if(getScrollX() <= initX){int dx = (int)(mWidth * mMenuWeight);mScroller.startScroll(getScrollX(), 0, dx, 0, 500);if(mListener != null){mListener.onChanged();}invalidate();}}public interface OnMenuChangedListener{public void onChanged();}   public void setOnMenuChangedListener(OnMenuChangedListener listener){mListener = listener;}
}

MainActivity.java

package com.example.testscrollto;import android.app.Activity;
import android.os.Bundle;
import android.view.View;import com.example.testscrollto.MyScrollView.OnMenuChangedListener;public class MainActivity extends Activity {private MyScrollView mScrollView;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mScrollView = (MyScrollView)findViewById(R.id.rightscrollview);final View menu = getLayoutInflater().inflate(R.layout.rightscrollview_menu, null);final View primary = getLayoutInflater().inflate(R.layout.rightscrollview_primary, null);final View rightview = getLayoutInflater().inflate(R.layout.rightscrollview_right_menu, null);mScrollView.setMenu(menu);mScrollView.setPrimary(primary);mScrollView.setRightView(rightview);mScrollView.setOnMenuChangedListener(new OnMenuChangedListener() {@Overridepublic void onChanged() {System.out.println("窗体切换了一次");}});}
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical" ><com.example.testscrollto.MyScrollViewandroid:id="@+id/rightscrollview"android:layout_width="match_parent"android:layout_height="match_parent" /></LinearLayout>

其余三个视图界面无限制。能够自由定义，这里就不贴出来了。

4、执行效果：

源码下载：http://download.csdn.net/detail/lxq_xsyu/7232701

这样就能够实现左右滑动了，没有不论什么bug吗？

事实上这样看似是没有什么问题了，上面用于推断界面位置的代码在逻辑上看似是对的，可是在实际的应用中偶尔会出现错乱。

以下我们用第二种方式解决：

package com.example.jaohangui.view;import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.LinearLayout;
import android.widget.Scroller;public class MyScrollLeftRightView extends LinearLayout{private Scroller mScroller;private View mLeftView;  //坐标界面private View mMainView;  //中间主界面private View mRightView; //右边界面private float mMeasureWight = 3.0f / 5; //菜单界面比例private int mWidth;    private int mHeight;private boolean isLocked = false;private boolean isToLeft = false;private static int CENTER_PAGE = 1;private static int LEFT_PAGE = 0;private static int RIGHT_PAGE = 2;private int currentPage = CENTER_PAGE;public MyScrollLeftRightView(Context context, AttributeSet attrs) {super(context, attrs);mScroller = new Scroller(context);}@Overrideprotected void onLayout(boolean changed, int l, int t, int r, int b) {super.onLayout(changed, l, t, r, b);mLeftView.layout(-(int)(mWidth * mMeasureWight), 0, 0, mHeight);mMainView.layout(0, 0, mWidth, mHeight);mRightView.layout(mWidth, 0, mWidth + (int)(mWidth * mMeasureWight), mHeight);}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {super.onMeasure(widthMeasureSpec, heightMeasureSpec);mWidth = MeasureSpec.getSize(widthMeasureSpec);mHeight = MeasureSpec.getSize(heightMeasureSpec);}/*** 加入左边界面内容* @param view*/public void setLeftView(View view){mLeftView = view;addView(mLeftView);}/*** 加入主界面内容* @param view*/public void setMainView(View view){mMainView = view;addView(mMainView);}/*** 加入右边界面内容* @param view*/public void setRightView(View view){mRightView = view;addView(mRightView);}private float mDownX;@Overridepublic boolean onTouchEvent(MotionEvent event) {float x = event.getX();switch (event.getAction()) {case MotionEvent.ACTION_DOWN:mDownX = x;break;case MotionEvent.ACTION_UP:int dis = (int)(x - mDownX); //滑动的距离if(Math.abs(dis) > (mWidth * mMeasureWight / 3)){if(dis > 0){toRightMove();}else{toLeftMove();}}break;default:break;}return true;}@Overridepublic void computeScroll() {super.computeScroll();if(mScroller.computeScrollOffset()){isLocked = true;scrollTo(mScroller.getCurrX(), mScroller.getCurrY());postInvalidate();}else{if(currentPage == CENTER_PAGE){if(isToLeft){currentPage = RIGHT_PAGE;}else{currentPage = LEFT_PAGE;}}else{currentPage = CENTER_PAGE;}isLocked = false;}}public void toRightMove(){if(currentPage == LEFT_PAGE || isLocked){return;}int dx = (int)(mWidth * mMeasureWight);mScroller.startScroll(getScrollX(), 0, -dx, 0, 500);invalidate();isToLeft = false;}public void toLeftMove(){if(currentPage == RIGHT_PAGE || isLocked){return;}System.out.println("ok");int dx = (int)(mWidth * mMeasureWight);mScroller.startScroll(getScrollX(), 0, dx, 0, 500);invalidate();isToLeft = true;}
}

上面使用了两个用来推断的变量和一个锁定状态（不让进入toLeftMove和toRightMove）的变量。

1、在进入toLeftMove或者toRightMove方法的时候首先会推断是否isLocked为true，假设为true则说明当前是正在滑动状态，不能够执行这两个方法。假设不这样去控制。在界面正在滑动的时候上面的currentPage就会发生错乱。

2、将要滑动之前告诉computeScroll()方法，是从toLeftMove和toRightMove的那个方法中出来的（使用isToLeft）。

3、最后推断Scroller是否已经停止滑动（移动），假设停止则改变当前页面的状态（currentPage的值）

有的时候我们尽管实现了一个功能或者某个逻辑，而怎样才干使这段代码更加健壮和有效更值得我们去认真思考。

。。