android使用viewpager计算偏移量实现选项卡功能

<?  version=\"1.0\" encoding=\"utf-8\"?>
<LinearLayout
  ns:android=\"http://schemas.android.com/apk/res/android\"
 android:orientation=\"vertical\"
 android:layout_width=\"match_parent\"
 android:layout_height=\"match_parent\"
 android:clipToPadding=\"true\"
 android:fitsSystemWindows=\"true\"
 android:background=\"@color/bg_color\">

 <LinearLayout
  android:layout_width=\"match_parent\"
  android:layout_height=\"match_parent\"
  android:background=\"@color/bag_gray\"
  android:orientation=\"vertical\">

  <LinearLayout
   android:layout_width=\"match_parent\"
   android:layout_height=\"36dp\"
   android:background=\"@android:color/white\"
   android:orientation=\"horizontal\"
   android:weightSum=\"3\">

   <TextView
    android:id=\"@+id/tab1_tv\"
    android:layout_width=\"0dp\"
    android:layout_height=\"wrap_content\"
    android:layout_gravity=\"center\"
    android:layout_weight=\"1\"
    android:gravity=\"center\"
    android:text=\"商品\"
    android:textColor=\"@color/ _bag\"
    android:textSize=\"18sp\" />

   <TextView
    android:id=\"@+id/tab2_tv\"
    android:layout_width=\"0dp\"
    android:layout_height=\"wrap_content\"
    android:layout_gravity=\"center\"
    android:layout_weight=\"1\"
    android:gravity=\"center\"
    android:text=\"评价\"
    android:textColor=\"@color/text_color_context\"
    android:textSize=\"18sp\" />
   <TextView
    android:id=\"@+id/tab3_tv\"
    android:layout_width=\"0dp\"
    android:layout_height=\"wrap_content\"
    android:layout_gravity=\"center\"
    android:layout_weight=\"1\"
    android:gravity=\"center\"
    android:text=\"详情\"
    android:textColor=\"@color/text_color_context\"
    android:textSize=\"18sp\" />

  </LinearLayout>

  <View
   android:layout_width=\"match_parent\"
   android:layout_height=\"0.5dp\"
   android:background=\"@color/text_color_context\" />
  <View
   android:id=\"@+id/cursor\"
   android:layout_width=\"50dp\"
   android:layout_height=\"2dp\"
   android:layout_marginLeft=\"40dp\"
   android:layout_marginTop=\"0dip\"
   android:background=\"@color/ _bag\"
   />
  <android.support.v4.view.ViewPager
   android:id=\"@+id/thire_vp\"
   android:layout_width=\"match_parent\"
   android:layout_height=\"match_parent\"/>
 </LinearLayout>

</LinearLayout>

public class FragmentAdapter extends FragmentPagerAdapter {
 private ArrayList<Fragment> list;
 FragmentManager fm;

 public FragmentAdapter(FragmentManager fm, ArrayList<Fragment> list){
  super(fm);
  this.fm = fm;
  this.list = list;
 }

 @Override
 public Fragment getItem(int position) {
  return list.get(position);
 }

 @Override
 public int getCount() {
  return list.size();
 }
}

public class OneFragment extends Fragment {

 @Nullable
 @Override
 public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
  View view = inflater.inflate(R.layout.fragment_one,null);
  return view;
 }
}

public class MainActivity extends FragmentActivity implements ViewPager.OnPageChangeListener,View. Listener{
 private TextView tab1Tv;
 private TextView tab2Tv;
 private TextView tab3Tv;
 private View cursor;
 private ViewPager thirdVp;

 private ArrayList<Fragment> fragmentlist;
 private int offset = 0;
 private int screenWidth = 0;
 private int screenl_3;
 private LinearLayout.LayoutParams lp;

 @Override
 protected void onCreate(@Nullable Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_product);

  //绑定控件
  tab1Tv = (TextView)findViewById(R.id.tab1_tv);
  tab2Tv = (TextView)findViewById(R.id.tab2_tv);
  tab3Tv = (TextView)findViewById(R.id.tab3_tv);
  cursor = (View) findViewById(R.id.cursor);
  thirdVp = (ViewPager) findViewById(R.id.thire_vp);

  //获取屏幕宽度
  DisplayMetrics dm = new DisplayMetrics();
  getWindowManager().getDefaultDisplay().getMetrics(dm);
  screenWidth = dm.widthPixels;
  screenl_3 = screenWidth/3; //裁剪3分之1
  lp = (LinearLayout.LayoutParams)cursor.getLayoutParams();

  fragmentlist = new ArrayList<>();
  fragmentlist.add(new OneFragment());
  fragmentlist.add(new TwoFragment());
  fragmentlist.add(new ThreeFragment());

  thirdVp.setAdapter(new FragmentAdapter(getSupportFragmentManager(),fragmentlist));
  thirdVp.setCurrentItem(0);
  thirdVp.setOffscreenPageLimit(2);

  thirdVp.setOnPageChangeListener(this);
  tab1Tv.set Listener(this);
  tab2Tv.set Listener(this);
  tab3Tv.set Listener(this);
 }

 @Override
 public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
  offset = (screenl_3-cursor.getLayoutParams().width)/2;
  Log.d(\"TAG\", \"111----\"+position + \"--\" + positionOffset + \"--\"
    + positionOffsetPixels);
  final float scale = getResources().getDisplayMetrics().density;
  if (position == 0){
   lp.leftMargin = (int)(positionOffsetPixels/3)+offset;
  }else if(position ==1){
   lp.leftMargin = (int)(positionOffsetPixels/3)+screenl_3+offset;
  }
  cursor.setLayoutParams(lp);
  upTextcolor(position);
 }

 private void upTextcolor(int position){
  if (position==0){
   tab1Tv.setTextColor(getResources().getColor(R.color. _bag));
   tab2Tv.setTextColor(getResources().getColor(R.color.text_color_context));
   tab3Tv.setTextColor(getResources().getColor(R.color.text_color_context));
  }else if(position==1){
   tab1Tv.setTextColor(getResources().getColor(R.color.text_color_context));
   tab2Tv.setTextColor(getResources().getColor(R.color. _bag));
   tab3Tv.setTextColor(getResources().getColor(R.color.text_color_context));
  }else if(position==2){
   tab1Tv.setTextColor(getResources().getColor(R.color.text_color_context));
   tab2Tv.setTextColor(getResources().getColor(R.color.text_color_context));
   tab3Tv.setTextColor(getResources().getColor(R.color. _bag));
  }
 }


 @Override
 public void onPageSelected(int position) {

 }

 @Override
 public void onPageScrollStateChanged(int state) {

 }

 @Override
 public void  (View view) {
  switch (view.getId()) {
   case R.id.tab1_tv:
    thirdVp.setCurrentItem(0);
    break;
   case R.id.tab2_tv:
    thirdVp.setCurrentItem(1);
    break;
   case R.id.tab3_tv:
    thirdVp.setCurrentItem(2);
    break;
  }
 }
}