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; } }}