android使用viewpager计算偏移量实现选项卡功能

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

 public FragmentAdapter(FragmentManager fm, ArrayList 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 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;
 }
 }
}