android使用viewpager计算偏移量实现选项卡功能

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
 xmlns: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/title_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/title_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.OnClickListener{
 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.setOnClickListener(this);
 tab2Tv.setOnClickListener(this);
 tab3Tv.setOnClickListener(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.title_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.title_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.title_bag));
 }
 }


 @Override
 public void onPageSelected(int position) {

 }

 @Override
 public void onPageScrollStateChanged(int state) {

 }

 @Override
 public void onClick(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;
 }
 }
}