Android 左右滑屏 方向判断 ViewPager

如题，左右的时候需要预加载，所有要知道方向，但是原来的控件没有这个方法，所有，修改了下，代码如下做一个备份，欢迎指正！

原文：http://www.cnblogs.com/meiyitian/archive/2012/01/29/2330994.html

package com.meityitian.app.views;

import android.content.Context;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.util.Log;

import com.meityitian.app.utils.Debug;

/**
 * 重写，添加了判定滑动方向的方法
 * @author zxy
 *
 */
public class meityitianViewPager extends ViewPager {
    private boolean left = false;
    private boolean right = false;
    private boolean isScrolling = false;
    private int lastValue = -1;
    private ChangeViewCallback changeViewCallback = null;

    public meityitianViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public meityitianViewPager(Context context) {
        super(context);
        init();
    }

    /**
     * init method .
*/
    private void init() {
        setOnPageChangeListener(listener);
    }

    /**
     * listener ,to get move direction .
*/
    public  OnPageChangeListener listener = new OnPageChangeListener() {
        @Override
        public void onPageScrollStateChanged(int arg0) {
            if (arg0 == 1) {
                isScrolling = true;
            } else {
                isScrolling = false;
            }

            Debug.infoByTag("meityitianViewPager",
                    "meityitianViewPager  onPageScrollStateChanged : arg0:"
                            + arg0);
            if (arg0 == 2) {
                Debug.infoByTag("meityitianViewPager",
                        "meityitianViewPager  onPageScrollStateChanged  direction left ? "
                                + left);
                Debug.infoByTag("meityitianViewPager",
                        "meityitianViewPager  onPageScrollStateChanged  direction right ? "
                                + right);
                //notify ....
                if(changeViewCallback!=null){
                    changeViewCallback.changeView(left, right);
                }
                right = left = false;
            }

        }

        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {
            if (isScrolling) {
                if (lastValue > arg2) {
                    // 递减，向右侧滑动
                    right = true;
                    left = false;
                } else if (lastValue < arg2) {
                    // 递减，向右侧滑动
                    right = false;
                    left = true;
                } else if (lastValue == arg2) {
                    right = left = false;
                }
            }
            Log.i("meityitianViewPager",
                    "meityitianViewPager onPageScrolled  last :arg2  ,"
                            + lastValue + ":" + arg2);
            lastValue = arg2;
        }

        @Override
        public void onPageSelected(int arg0) {
            if(changeViewCallback!=null){
                changeViewCallback.getCurrentPageIndex(arg0);
            }
        }
    };
    
    /**
     * 得到是否向右侧滑动
     * @return true 为右滑动
*/
    public boolean getMoveRight(){
        return right;
    }
    
    /**
     * 得到是否向左侧滑动
     * @return true 为左做滑动
*/
    public boolean getMoveLeft(){
        return left;
    }
    
    /**
     *  滑动状态改变回调
     * @author zxy
     *
*/
    public interface ChangeViewCallback{
        /**
         * 切换视图 ？决定于left和right 。
         * @param left
         * @param right
*/
        public  void changeView(boolean left,boolean right);
        public  void  getCurrentPageIndex(int index);
    }
    
    /**
     * set ...
     * @param callback
*/
    public void  setChangeViewCallback(ChangeViewCallback callback){
        changeViewCallback = callback;
    }
}