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 < titles.length; i++) {     TextView textView = new TextView(context);    textView.setLayoutParams(new LayoutParams(0,      dip2px(HEIGHT_NAVIGATION_BAR), 1));    textView.setText(titles[i]);    textView.setGravity(Gravity.CENTER);    textView.setTextSize(16);    textView.setTextColor(getResources()      .getColor(android.R.color.white));    textView.setId(i);    textView.setOnClickListener(this);    ll_navigation.addView(textView);   }   // 添加导航   this.addView(ll_navigation);    // 指示器布局   LinearLayout ll_indicator = new LinearLayout(context);   ll_indicator.setLayoutParams(new LayoutParams(     LayoutParams.MATCH_PARENT, dip2px(HEIGHT_INDICATOR)));   ll_indicator.setBackgroundColor(getResources().getColor(     android.R.color.holo_blue_light));   ll_indicator.setOrientation(HORIZONTAL);    // 指示器   ivBottomLine = new ImageView(context);   ivBottomLine.setImageResource(android.R.color.holo_orange_light);   ivBottomLine.setScaleType(ScaleType.MATRIX);   ivBottomLine     .setLayoutParams(new LinearLayout.LayoutParams(       getScreenWidth(context) / titleCount,       dip2px(HEIGHT_INDICATOR)));   ll_indicator.addView(ivBottomLine);   // 添加指示器   this.addView(ll_indicator);    viewGroup.addView(this);   viewPager.setOnPageChangeListener(this);    // 初始化移动位置   positions = new int[titleCount];   positions[0] = 0;   int distance = (int) (getScreenWidth(context) / titleCount);   for (int i = 1; i < titleCount; i++) {    positions[i] = distance * i;   }   }   @Override  public void onClick(View v) {   viewPager.setCurrentItem(v.getId());  }   @Override  public void onPageScrollStateChanged(int arg0) {   }   @Override  public void onPageScrolled(int position, float positionOffset,    int positionOffsetPixels) {   }   @Override  public void onPageSelected(int position) {    Animation animation = new TranslateAnimation(currIndex * positions[1],     positions[position], 0, 0);   currIndex = position;   animation.setFillAfter(true);   animation.setDuration(300);   ivBottomLine.startAnimation(animation);  }   private int dip2px(float dpValue) {   final float scale = context.getResources().getDisplayMetrics().density;   return (int) (dpValue * scale + 0.5f);  }   // 获取屏幕宽度  private int getScreenWidth(Context context) {   DisplayMetrics dm = new DisplayMetrics();   ((Activity) context).getWindowManager().getDefaultDisplay()     .getMetrics(dm);   return dm.widthPixels;  } }