Android实现带有指示器的自定义底部导航栏

package com.example.indicatornavigationbar; 
 
import android.app.Activity; 
import android.content.Context; 
import android.support.v4.view.ViewPager; 
import android.support.v4.view.ViewPager.OnPageChangeListener; 
import android.util.DisplayMetrics; 
import android.view.Gravity; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.view.ViewGroup; 
import android.view.animation.Animation; 
import android.view.animation.TranslateAnimation; 
import android.widget.ImageView; 
import android.widget.ImageView.ScaleType; 
import android.widget.LinearLayout; 
import android.widget.TextView; 
 
/** 
 * 
 * @ClassName: com.mengle.activity.IndicatorNavigationBar 
 * @Description: 带有指示器的底部导航栏 
 * @author zhaokaiqiang 
 * @date 2014-10-17 上午11:07:40 
 * 
 */ 
public class IndicatorNavigationBar extends LinearLayout implements 
  OnClickListener, OnPageChangeListener { 
 
 // 导航栏默认高度，不包括指示器高度，单位是dp 
 private static final int HEIGHT_NAVIGATION_BAR = 40; 
 // 指示器默认高度，单位是dp 
 private static final int HEIGHT_INDICATOR = 4; 
 
 private Context context; 
 private ViewPager viewPager; 
 // 指示器 
 private ImageView ivBottomLine; 
 // 当前显示的index 
 private int currIndex = 0; 
 // 存储移动位置 
 private int positions[]; 
 // 标题数量 
 private int titleCount; 
 
 public IndicatorNavigationBar(Context context) { 
  super(context); 
  this.context = context; 
 } 
 
 /** 
  * 
  * @Description: 依附到父布局上 
  * @param viewGroup 
  *   要依附在的父布局 
  * @param titles 
  *   底部显示的导航文字 
  * @param viewPager 
  *   绑定的ViewPager对象 
  * @return void 
  */ 
 public void attachToParent(ViewGroup viewGroup, String[] titles, 
   ViewPager viewPager) { 
 
  this.viewPager = viewPager; 
  titleCount = titles.length; 
 
  // 初始化主布局 
  setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, 
    dip2px(HEIGHT_NAVIGATION_BAR + HEIGHT_INDICATOR))); 
  setBackgroundColor(getResources().getColor(android.R.color.transparent)); 
  setOrientation(VERTICAL); 
 
  // 导航栏布局 
  LinearLayout ll_navigation = new LinearLayout(context); 
  ll_navigation.setLayoutParams(new LayoutParams( 
    LayoutParams.MATCH_PARENT, dip2px(HEIGHT_NAVIGATION_BAR))); 
  ll_navigation.setBackgroundColor(getResources().getColor( 
    android.R.color.holo_blue_light)); 
  ll_navigation.setOrientation(HORIZONTAL); 
 
  // 生成导航按钮(TextView) 
  for (int i = 0; i