文章目录

• 二级页面首页的ViewPager页面切换
• • 效果展示
  • 代码实现
  • • 创建几个三级页面Fragment视图
    • ViewPager的Fragment数据丢失问题
    • 创建fragment_home视图文件
    • HomeFragment.java

二级页面首页的ViewPager页面切换

效果展示

代码实现

创建几个三级页面Fragment视图

import android.graphics.Color; import android.os.Bundle; import android.support.annotation.NonNull; import android.support.annotation.Nullable; import android.support.v4.app.Fragment; import android.view.Gravity; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.TextView;public class Page1Fragment extends Fragment {View view = null;@Nullable@Overridepublic View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {//判断view是否为空if(view==null) {view = getMyView();}else {//清除当前重用的view的parentViewGroup viewGroup = (ViewGroup) view.getParent();if (viewGroup!=null){viewGroup.removeView(view) ;}}return view;}private View getMyView() {TextView textView= new TextView(getActivity());textView.setBackgroundColor(Color.GRAY);textView.setText("页面1");textView.setTextSize(30);textView.setGravity(Gravity.CENTER);return textView;} }

ViewPager的Fragment数据丢失问题

一般用ViewPager滑动页面时会出现数据丢失的问题

• 当Fragment滑出屏幕的时候，系统调onDestoryView方法
  销毁视图
• 当Fragment重新滑入屏幕的时候，系统调onCreateView方法
  创建新的视图

//清除当前重用的view的parentViewGroup viewGroup = (ViewGroup) view.getParent();if (viewGroup!=null){viewGroup.removeView(view) ;}

上述代码可以解决数据丢失问题

创建fragment_home视图文件

TabLayout需要引入依赖
implementation ‘com.android.support:design:28.0.0’

<?xml version="1.0" encoding="utf-8"?> <LinearLayout android:orientation="vertical"android:layout_width="match_parent"android:layout_height="match_parent"xmlns:android="http://schemas.android.com/apk/res/android"xmlns:app="http://schemas.android.com/apk/res-auto"><!--app:tabMode="scrollable" 如果标题过多，滑动 --><android.support.design.widget.TabLayoutandroid:id="@+id/tl_home"app:tabMode="scrollable"app:tabTextColor="#242424"app:tabIndicatorHeight="6dp"app:tabIndicatorFullWidth="false"app:tabSelectedTextColor="#F04445"android:layout_width="match_parent"android:layout_height="40dp"></android.support.design.widget.TabLayout><android.support.v4.view.ViewPagerandroid:id="@+id/vp_home"android:layout_width="match_parent"android:layout_height="match_parent"></android.support.v4.view.ViewPager></LinearLayout>

HomeFragment.java

import android.graphics.Color; import android.os.Bundle; import android.support.annotation.NonNull; import android.support.annotation.Nullable; import android.support.design.widget.TabLayout; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentPagerAdapter; import android.support.v4.view.ViewPager; import android.view.Gravity; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.ArrayAdapter; import android.widget.TextView;import com.example.administrator.zhjrtt.R; import com.xzit.fragment.sub.Page1Fragment; import com.xzit.fragment.sub.Page2Fragment; import com.xzit.fragment.sub.Page3Fragment; import com.xzit.fragment.sub.Page4Fragment;import java.util.ArrayList; import java.util.List;public class HomeFragment extends Fragment {class MyPagerAdapter extends FragmentPagerAdapter{//创建集合存放页面private List<Fragment> pages = new ArrayList<>();//创建集合存放指示器标题private List<String> titles = new ArrayList<>();public MyPagerAdapter(FragmentManager fm) {super(fm);//将初始化Fragment页面放入页面集合pages.add(new Page1Fragment());pages.add(new Page2Fragment());pages.add(new Page3Fragment());pages.add(new Page4Fragment());//将标题内容放入集合titles.add("Page1Fragment");titles.add("Page2Fragment");titles.add("Page3Fragment");titles.add("Page4Fragment");}@Nullable@Overridepublic CharSequence getPageTitle(int position) {//返回指定位置标题内容return titles.get(position);}@Overridepublic Fragment getItem(int i) {//返回页面内容return pages.get(i);}@Overridepublic int getCount() {//返回页面数量return pages.size();}}@Nullable@Overridepublic View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {View view = getMyView();return view;}private View getMyView() {//1.布局viewpager//2.加载View view = View.inflate(getActivity(),R.layout.fragment_home,null);ViewPager viewPager = view.findViewById(R.id.vp_home);//3.定义适配器//4.初始化设置适配器MyPagerAdapter myPagerAdapter = new MyPagerAdapter(getFragmentManager());viewPager.setAdapter(myPagerAdapter);//5.初始化指示器TabLayout tabLayout = view.findViewById(R.id.tl_home);tabLayout.setupWithViewPager(viewPager);//->viewpager-->adapter->getPageTitlereturn view;} }

总结

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