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androidx下的fragment的lazy懒加载问题

androidx下的fragment的lazy懒加载问题

作者: kaxi4it | 来源:发表于2020-04-14 10:49 被阅读0次

    网上关于androidx的fragment懒加载文章已经有很多，各有侧重。几乎都点到了sexMaxLifecycle和修改FragmentPagerAdapter。很少看到经过实践的文章，谨以此文，更加详尽的把实践后的结果记录下来，赠予有缘人。

    一、前置准备工作

    几个关于androidx的fragment懒加载方案，都离不开如下几个包：

    • androidx.fragment:fragment:1.1.0-alpha07 以上，支持setMaxLifecycle方法即可
    • androidx.viewpager:viewpager:1.0.0 以上，如果涉及到viewpager内的fragment使用

    我在实际测试代码中使用了如下版本，可供参考：

    • androidx.fragment:fragment:1.2.4
    • androidx.viewpager:viewpager:1.0.0
    • FlycoTabLayout

    还准备了4个Activity与5个Fragment：

    • AddShowHideFragmentActivity 通过add show显示的案例
    • AddShowHideFragmentInFragmentActivity 嵌套在fragment中的，通过add show显示的fragment案例
    • ViewPagerFragmentActivity 通过ViewPager滑动显示的案例
    • ViewPagerFragmentInFragmentActivity 嵌套在fragment中的，通过ViewPager滑动显示的案例
    • AddFragmentInFragment 操作add show的fragment
    • ViewPagerFragmentInFragment 操作ViewPager的fragment
    • BlankFragment1 打印生命周期日志的空页面1
    • BlankFragment2 打印生命周期日志的空页面2
    • BlankFragment3 打印生命周期日志的空页面3

    相应的几个简单布局文件:

    • 文件：fragment_main.xml
      加载ViewPager控件和AddShow使用的FrameLayout，以及测试跳转后返回的TextView按钮。
    fragment_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/vp_fragment"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        />

    <com.flyco.tablayout.CommonTabLayout
        android:id="@+id/tab_title"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@color/colorPrimary"
        app:tl_indicator_color="@color/colorAccent"
        app:tl_indicator_height="2dp"
        app:tl_indicator_width="30dp"
        app:tl_tab_space_equal="true"
        app:tl_textBold="SELECT"
        app:tl_textSelectColor="#000000"
        app:tl_textUnselectColor="#333333"
        app:layout_constraintTop_toBottomOf="@id/vp_fragment"
        app:layout_constraintLeft_toLeftOf="parent"
        />

    <FrameLayout
        android:id="@+id/fl_in_content"
        android:layout_width="match_parent"
        android:layout_height="200dp"
        app:layout_constraintTop_toBottomOf="@id/tab_title"
        />

    <TextView
        android:id="@+id/tv_next"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:text="next"
        android:gravity="center"
        app:layout_constraintBottom_toBottomOf="parent"
        />

</androidx.constraintlayout.widget.ConstraintLayout>
    • 文件：activity_lazy_fragment.xml
      这里是测试fragment嵌套情况下的布局，fl_content用来加载fragment
    activity_lazy_fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".lazyFragment.ViewPagerFragmentActivity">

    <FrameLayout
        android:id="@+id/fl_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        />

</androidx.constraintlayout.widget.ConstraintLayout>
    • 文件：fragment_blank.xml
      这一个空fragment就没什么讲究了
    fragment_blank.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >

    <TextView
        android:id="@+id/tv_fragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:text="" />

</FrameLayout>

    二、具体代码分析

    1) ViewPager+Fragment

    最常见的使用方式，由ViewPager滑动显示多个Fragment，直接上代码：

    • activity页面代码
      其中就是个简单的viewpager设置adapter然后加载fragment集合显示
    /**
 * viewpager内的fragment懒加载
 */
public class ViewPagerFragmentActivity extends BindActivity implements BlankFragment1.OnFragmentInteractionListener , BlankFragment2.OnFragmentInteractionListener, BlankFragment3.OnFragmentInteractionListener {

    private static final String KEY_FRAGMENT_1 = "1";
    private static final String KEY_FRAGMENT_2 = "2";
    private static final String KEY_FRAGMENT_3 = "3";
    @BindView(R.id.vp_fragment)
    ViewPager vp;
    @BindView(R.id.tv_next)
    TextView tv_next;
    BlankFragment1 blankFragment1;
    BlankFragment2 blankFragment2;
    BlankFragment3 blankFragment3;
    List<Fragment> fragmentList;
    @Override
    protected int setLayoutID() {
        return R.layout.fragment_main;
    }

    @Override
    protected void initViews(Bundle savedInstanceState) {

        tv_next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(mContext, MMKVActivity.class);
                startActivity(intent);
            }
        });

        if(savedInstanceState != null){
            blankFragment1 = (BlankFragment1)getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_1);
            blankFragment2 = (BlankFragment2)getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_2);
            blankFragment3 = (BlankFragment3)getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_3);
        }

        fragmentList=new ArrayList<>();
        if (blankFragment1==null){
            fragmentList.add(blankFragment1=BlankFragment1.newInstance("11111",""));
        }else {
            fragmentList.add(blankFragment1);
        }
        if (blankFragment2==null){
            fragmentList.add(blankFragment2=BlankFragment2.newInstance("22222",""));
        }else {
            fragmentList.add(blankFragment2);
        }
        if (blankFragment3==null){
            fragmentList.add(blankFragment3=BlankFragment3.newInstance("333333",""));
        }else {
            fragmentList.add(blankFragment3);
        }

        vp.setAdapter(new BaseFragmentXPagerAdapter(getSupportFragmentManager(),fragmentList,null));

    }

    @Override
    public void onFragmentInteraction(Uri uri) {
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        if(blankFragment1 != null&&blankFragment1.isAdded()) {
            getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_1,blankFragment1);
        }
        if(blankFragment2 != null&&blankFragment2.isAdded()){
            getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_2,blankFragment2);
        }
        if(blankFragment3 != null&&blankFragment3.isAdded()){
            getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_3,blankFragment3);
        }
        super.onSaveInstanceState(outState);
    }
}
    • BaseFragmentXPagerAdapter页面代码
      新版FragmentPagerAdapter多了2个常量
    @Retention(RetentionPolicy.SOURCE)
    @IntDef({BEHAVIOR_SET_USER_VISIBLE_HINT, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT})
    private @interface Behavior { }

    用在了构造方法中

    /**
     * Constructor for {@link FragmentPagerAdapter}.
     *
     * If {@link #BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT} is passed in, then only the current
     * Fragment is in the {@link Lifecycle.State#RESUMED} state. All other fragments are capped at
     * {@link Lifecycle.State#STARTED}. If {@link #BEHAVIOR_SET_USER_VISIBLE_HINT} is passed, all
     * fragments are in the {@link Lifecycle.State#RESUMED} state and there will be callbacks to
     * {@link Fragment#setUserVisibleHint(boolean)}.
     *
     * @param fm fragment manager that will interact with this adapter
     * @param behavior determines if only current fragments are in a resumed state
     */
    public FragmentPagerAdapter(@NonNull FragmentManager fm,
            @Behavior int behavior) {
        mFragmentManager = fm;
        mBehavior = behavior;
    }

    我们只需要在构造adapter时，使用BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT这个常量就行

    /**
 * support lazy init
 */
public class BaseFragmentXPagerAdapter extends FragmentPagerAdapter {

    private List<Fragment> mFragmentList = new ArrayList<>();
    private List<String> mFragmentTitleList = new ArrayList<>();

    public BaseFragmentXPagerAdapter(@NonNull FragmentManager fm,List<Fragment> fragmentList,List<String> fragmentTitleList) {
        this(fm,fragmentList,fragmentTitleList,BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
    }
    public BaseFragmentXPagerAdapter(@NonNull FragmentManager fm,List<Fragment> fragmentList,List<String> fragmentTitleList, int behavior) {
        super(fm, behavior);
        if (fragmentList!=null){
            mFragmentList.addAll(fragmentList);
        }
        if (fragmentTitleList!=null){
            mFragmentTitleList.addAll(fragmentTitleList);
        }
    }

    public BaseFragmentXPagerAdapter(@NonNull FragmentManager fm,Fragment[] fragmentList,String[] fragmentTitleList) {
        this(fm,fragmentList,fragmentTitleList,BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
    }
    public BaseFragmentXPagerAdapter(@NonNull FragmentManager fm,Fragment[] fragmentList,String[] fragmentTitleList, int behavior) {
        super(fm, behavior);
        if (fragmentList!=null){
            for (int i = 0; i < fragmentList.length; i++) {
                mFragmentList.add(fragmentList[i]);
            }
        }
        if (fragmentTitleList!=null){
            for (int i = 0; i < fragmentTitleList.length; i++) {
                mFragmentTitleList.add(fragmentTitleList[i]);
            }
        }
    }

    @NonNull
    @Override
    public Fragment getItem(int position) {
        if (mFragmentList!=null&&!mFragmentList.isEmpty()){
            return mFragmentList.get(position);
        }else {
            return null;
        }
    }

    @Override
    public int getCount() {
        if (mFragmentList!=null&&!mFragmentList.isEmpty()){
            return mFragmentList.size();
        }else {
            return 0;
        }
    }

    @Nullable
    @Override
    public CharSequence getPageTitle(int position) {
        if (mFragmentTitleList!=null&&!mFragmentTitleList.isEmpty()&&position<mFragmentTitleList.size()){
            return mFragmentTitleList.get(position);
        }else {
            return null;
        }
    }
}

    最终打印生命周期日志，确认结果，viewPager+fragment搭配pagerAdapter的behavior在各种情况下的日志，可以看出新版viewPager+pagerAdapter实测下来，Fragment的onResume生命周期只会在当前页显示时调用：

    • 首次进入 显示第一页
      ViewPagerFragmentActivity--->onCreate
      ViewPagerFragmentActivity--->onStart
      ViewPagerFragmentActivity--->onResume
      BlankFragment1--->onAttach
      BlankFragment1--->onCreate
      BlankFragment2--->onAttach
      BlankFragment2--->onCreate
      BlankFragment1--->onViewCreated
      BlankFragment1--->onActivityCreated
      BlankFragment1--->onStart
      BlankFragment2--->onViewCreated
      BlankFragment2--->onActivityCreated
      BlankFragment2--->onStart
      BlankFragment1--->onResume <<=================== 当前页
    • 滑动到第二页
      BlankFragment3--->onAttach
      BlankFragment3--->onCreate
      BlankFragment3--->onViewCreated
      BlankFragment3--->onActivityCreated
      BlankFragment3--->onStart
      BlankFragment1--->onPause
      BlankFragment2--->onResume <<=================== 当前页
    • 锁屏
      BlankFragment2--->onPause
      ViewPagerFragmentActivity--->onPause
      BlankFragment1--->onStop
      BlankFragment2--->onStop
      BlankFragment3--->onStop
      ViewPagerFragmentActivity--->onStop
      ViewPagerFragmentActivity--->onSaveInstanceState
    • 解锁屏幕
      ViewPagerFragmentActivity--->onRestart
      BlankFragment1--->onStart
      BlankFragment2--->onStart
      BlankFragment3--->onStart
      ViewPagerFragmentActivity--->onStart
      ViewPagerFragmentActivity--->onResume
      BlankFragment2--->onResume <<=================== 当前页
    • HOME回到桌面
      BlankFragment2--->onPause
      ViewPagerFragmentActivity--->onPause
      BlankFragment1--->onStop
      BlankFragment2--->onStop
      BlankFragment3--->onStop
      ViewPagerFragmentActivity--->onStop
      ViewPagerFragmentActivity--->onSaveInstanceState
    • 返回app页面
      ViewPagerFragmentActivity--->onRestart
      BlankFragment1--->onStart
      BlankFragment2--->onStart
      BlankFragment3--->onStart
      ViewPagerFragmentActivity--->onStart
      ViewPagerFragmentActivity--->onResume
      BlankFragment2--->onResume <<=================== 当前页
    • 跳转新页面
      BlankFragment2--->onPause
      ViewPagerFragmentActivity--->onPause
      MMKVActivity--->onCreate
      MMKVActivity--->onStart
      MMKVActivity--->onResume
      BlankFragment1--->onStop
      BlankFragment2--->onStop
      BlankFragment3--->onStop
      ViewPagerFragmentActivity--->onStop
      ViewPagerFragmentActivity--->onSaveInstanceState
    • 返回ViewPager的页面
      MMKVActivity--->onPause
      ViewPagerFragmentActivity--->onRestart
      BlankFragment1--->onStart
      BlankFragment2--->onStart
      BlankFragment3--->onStart
      ViewPagerFragmentActivity--->onStart
      ViewPagerFragmentActivity--->onResume
      BlankFragment2--->onResume <<=================== 当前页
      MMKVActivity--->onStop
      MMKVActivity--->onDestroy

    2) Fragment嵌套Fragment内的ViewPager+Fragment

    外层的activity只是add一个fragment

    /**
 * fragment内的viewpager内的fragment懒加载
 */
public class ViewPagerFragmentInFragmentActivity extends BindActivity implements ViewPagerFragmentInFragment.OnFragmentInteractionListener ,BlankFragment1.OnFragmentInteractionListener, BlankFragment2.OnFragmentInteractionListener, BlankFragment3.OnFragmentInteractionListener {

    @Override
    protected int setLayoutID() {
        return R.layout.activity_lazy_fragment;
    }

    @Override
    protected void initViews(Bundle savedInstanceState) {
        FragmentTransaction transaction=getSupportFragmentManager().beginTransaction();
        transaction.add(R.id.fl_content, ViewPagerFragmentInFragment.newInstance("",""));
        transaction.commit();
    }

    @Override
    public void onFragmentInteraction(Uri uri) {

    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
    }
}

    嵌套用的fragment类，ViewPagerFragmentInFragment

    /**
 * viewpager在一个fragment内
 */
public class ViewPagerFragmentInFragment extends BaseFragment {
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    private String mParam1;
    private String mParam2;

    private OnFragmentInteractionListener mListener;

    private static final String KEY_FRAGMENT_1 = "1";
    private static final String KEY_FRAGMENT_2 = "2";
    private static final String KEY_FRAGMENT_3 = "3";

    @BindView(R.id.vp_fragment)
    ViewPager vp;
    @BindView(R.id.tv_next)
    TextView tv_next;
    BlankFragment1 blankFragment1;
    BlankFragment2 blankFragment2;
    BlankFragment3 blankFragment3;
    List<Fragment> fragmentList;

    public ViewPagerFragmentInFragment() {
    }

    public static ViewPagerFragmentInFragment newInstance(String param1, String param2) {
        ViewPagerFragmentInFragment fragment = new ViewPagerFragmentInFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onSaveInstanceState(@NonNull Bundle outState) {

        if(blankFragment1 != null&&blankFragment1.isAdded()) {
            mActivity.getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_1,blankFragment1);
        }
        if(blankFragment2 != null&&blankFragment2.isAdded()){
            mActivity.getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_2,blankFragment2);
        }
        if(blankFragment3 != null&&blankFragment3.isAdded()){
            mActivity.getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_3,blankFragment3);
        }
        super.onSaveInstanceState(outState);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }

    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        tv_next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(mContext, MMKVActivity.class);
                startActivity(intent);
            }
        });

        if(savedInstanceState != null){
            blankFragment1 = (BlankFragment1)mActivity.getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_1);
            blankFragment2 = (BlankFragment2)mActivity.getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_2);
            blankFragment3 = (BlankFragment3)mActivity.getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_3);
        }

        fragmentList=new ArrayList<>();
        if (blankFragment1==null){
            fragmentList.add(blankFragment1=BlankFragment1.newInstance("11111",""));
        }else {
            fragmentList.add(blankFragment1);
        }
        if (blankFragment2==null){
            fragmentList.add(blankFragment2=BlankFragment2.newInstance("22222",""));
        }else {
            fragmentList.add(blankFragment2);
        }
        if (blankFragment3==null){
            fragmentList.add(blankFragment3=BlankFragment3.newInstance("333333",""));
        }else {
            fragmentList.add(blankFragment3);
        }

        vp.setAdapter(new BaseFragmentXPagerAdapter(mActivity.getSupportFragmentManager(),fragmentList,null));

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_main, container, false);
    }

    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    public interface OnFragmentInteractionListener {
        void onFragmentInteraction(Uri uri);
    }
}

    实测日志可以发现，哪怕fragment是嵌套过的，Fragment的onResume生命周期也只会在当前页显示时调用：

    • 首次进入显示第一页
      ViewPagerFragmentInFragment--->onStart
      ViewPagerFragmentInFragmentActivity--->onStart
      ViewPagerFragmentInFragmentActivity--->onResume
      ViewPagerFragmentInFragment--->onResume
      BlankFragment1--->onAttach
      BlankFragment1--->onCreate
      BlankFragment2--->onAttach
      BlankFragment2--->onCreate
      BlankFragment1--->onViewCreated
      BlankFragment1--->onActivityCreated
      BlankFragment1--->onStart
      BlankFragment2--->onViewCreated
      BlankFragment2--->onActivityCreated
      BlankFragment2--->onStart
      BlankFragment1--->onResume <<=================== 当前页
    • 滑动到第二页
      BlankFragment3--->onAttach
      BlankFragment3--->onCreate
      BlankFragment3--->onViewCreated
      BlankFragment3--->onActivityCreated
      BlankFragment3--->onStart
      BlankFragment1--->onPause
      BlankFragment2--->onResume <<=================== 当前页
    • 锁屏
      ViewPagerFragmentInFragment--->onPause
      BlankFragment2--->onPause
      ViewPagerFragmentInFragmentActivity--->onPause
      ViewPagerFragmentInFragment--->onStop
      BlankFragment1--->onStop
      BlankFragment2--->onStop
      BlankFragment3--->onStop
      ViewPagerFragmentInFragmentActivity--->onStop
      ViewPagerFragmentInFragmentActivity--->onSaveInstanceState
    • 解锁屏幕
      ViewPagerFragmentInFragmentActivity--->onRestart
      ViewPagerFragmentInFragment--->onStart
      BlankFragment1--->onStart
      BlankFragment2--->onStart
      BlankFragment3--->onStart
      ViewPagerFragmentInFragmentActivity--->onStart
      ViewPagerFragmentInFragmentActivity--->onResume
      ViewPagerFragmentInFragment--->onResume
      BlankFragment2--->onResume <<=================== 当前页
    • HOME回到桌面
      ViewPagerFragmentInFragment--->onPause
      BlankFragment2--->onPause
      ViewPagerFragmentInFragmentActivity--->onPause
      ViewPagerFragmentInFragment--->onStop
      BlankFragment1--->onStop
      BlankFragment2--->onStop
      BlankFragment3--->onStop
      ViewPagerFragmentInFragmentActivity--->onStop
      ViewPagerFragmentInFragmentActivity--->onSaveInstanceState
    • 返回app页面
      ViewPagerFragmentInFragmentActivity--->onRestart
      ViewPagerFragmentInFragment--->onStart
      BlankFragment1--->onStart
      BlankFragment2--->onStart
      BlankFragment3--->onStart
      ViewPagerFragmentInFragmentActivity--->onStart
      ViewPagerFragmentInFragmentActivity--->onResume
      ViewPagerFragmentInFragment--->onResume
      BlankFragment2--->onResume <<=================== 当前页
    • 跳转新页面
      ViewPagerFragmentInFragment--->onPause
      BlankFragment2--->onPause
      ViewPagerFragmentInFragmentActivity--->onPause
      MMKVActivity--->onCreate
      MMKVActivity--->onStart
      MMKVActivity--->onResume
      ViewPagerFragmentInFragment--->onStop
      BlankFragment1--->onStop
      BlankFragment2--->onStop
      BlankFragment3--->onStop
      ViewPagerFragmentInFragmentActivity--->onStop
      ViewPagerFragmentInFragmentActivity--->onSaveInstanceState
    • 返回ViewPager的页面
      MMKVActivity--->onPause
      ViewPagerFragmentInFragmentActivity--->onRestart
      ViewPagerFragmentInFragment--->onStart
      BlankFragment1--->onStart
      BlankFragment2--->onStart
      BlankFragment3--->onStart
      ViewPagerFragmentInFragmentActivity--->onStart
      ViewPagerFragmentInFragmentActivity--->onResume
      ViewPagerFragmentInFragment--->onResume
      BlankFragment2--->onResume <<=================== 当前页

    3) 通过add show hide操作多个fragment

    activity代码中的一个细节为通过add show的页面，设置transaction.setMaxLifecycle(fragment, Lifecycle.State.RESUMED)，让该fragment的生命周期能顺利走到resume；
    通过hide隐藏的页面，设置transaction.setMaxLifecycle(fragmentList.get(i), Lifecycle.State.CREATED)，使隐藏了的fragment生命周期只能走到创建阶段，无法走到resume方法。

    /**
 * add show hide下的fragment懒加载
 */
public class AddShowHideFragmentActivity extends BindActivity implements BlankFragment1.OnFragmentInteractionListener , BlankFragment2.OnFragmentInteractionListener, BlankFragment3.OnFragmentInteractionListener {

    private static final String KEY_FRAGMENT_1 = "1";
    private static final String KEY_FRAGMENT_2 = "2";
    private static final String KEY_FRAGMENT_3 = "3";
    @BindView(R.id.tab_title)
    CommonTabLayout commonTabLayout;
    @BindView(R.id.tv_next)
    TextView tv_next;
    BlankFragment1 blankFragment1;
    BlankFragment2 blankFragment2;
    BlankFragment3 blankFragment3;
    List<Fragment> fragmentList;
    @Override
    protected int setLayoutID() {
        return R.layout.fragment_main;
    }

    @Override
    protected void initViews(Bundle savedInstanceState) {
        tv_next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(mContext, MMKVActivity.class);
                startActivity(intent);
            }
        });
        if(savedInstanceState != null){
            blankFragment1 = (BlankFragment1)getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_1);
            blankFragment2 = (BlankFragment2)getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_2);
            blankFragment3 = (BlankFragment3)getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_3);
        }
        fragmentList=new ArrayList<>();
        if (blankFragment1==null){
            fragmentList.add(blankFragment1=BlankFragment1.newInstance("11111",""));
        }else {
            fragmentList.add(blankFragment1);
        }
        if (blankFragment2==null){
            fragmentList.add(blankFragment2=BlankFragment2.newInstance("22222",""));
        }else {
            fragmentList.add(blankFragment2);
        }
        if (blankFragment3==null){
            fragmentList.add(blankFragment3=BlankFragment3.newInstance("33333",""));
        }else {
            fragmentList.add(blankFragment3);
        }
        ArrayList<CustomTabEntity> tabEntities = new ArrayList<>();
        tabEntities.add(new TabLayoutEntity("商品1"));
        tabEntities.add(new TabLayoutEntity("评价2"));
        tabEntities.add(new TabLayoutEntity("详情3"));
        commonTabLayout.setTabData(tabEntities);
        commonTabLayout.setCurrentTab(0);
        showFragment(fragmentList.get(0),false);
        commonTabLayout.setOnTabSelectListener(new OnTabSelectListener() {
            @Override
            public void onTabSelect(int position) {
                showFragment(fragmentList.get(position),false);
            }

            @Override
            public void onTabReselect(int position) {
                showFragment(fragmentList.get(position),false);
            }
        });

    }

    private void showFragment(Fragment fragment,boolean replace){
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        if (replace){
            transaction.replace(R.id.fl_in_content,fragment);
        }else {
            if (!fragment.isAdded()){
                transaction.add(R.id.fl_in_content,fragment,fragment.getClass().getSimpleName());
            }
            hideAllFragment(transaction,fragment);
            transaction.show(fragment);
            transaction.setMaxLifecycle(fragment, Lifecycle.State.RESUMED);
        }
        transaction.commit();
    }
    private void hideAllFragment(FragmentTransaction transaction,Fragment withoutFragment){
        for (int i = 0; i < fragmentList.size(); i++) {
            if (!fragmentList.get(i).equals(withoutFragment)&&fragmentList.get(i).isAdded()){
                transaction.hide(fragmentList.get(i));
                transaction.setMaxLifecycle(fragmentList.get(i), Lifecycle.State.CREATED);
            }
        }
    }

    @Override
    public void onFragmentInteraction(Uri uri) {
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        if(blankFragment1 != null&&blankFragment1.isAdded()) {
            getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_1,blankFragment1);
        }
        if(blankFragment2 != null&&blankFragment2.isAdded()){
            getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_2,blankFragment2);
        }
        if(blankFragment3 != null&&blankFragment3.isAdded()){
            getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_3,blankFragment3);
        }
        super.onSaveInstanceState(outState);
    }
}
    • 首次进入 显示第一页
      AddShowHideFragmentActivity--->onCreate
      BlankFragment1--->onAttach
      BlankFragment1--->onCreate
      BlankFragment1--->onViewCreated
      BlankFragment1--->onActivityCreated
      BlankFragment1--->onStart
      AddShowHideFragmentActivity--->onStart
      AddShowHideFragmentActivity--->onResume
      BlankFragment1--->onResume <<=================== 当前页
    • 点击显示第二页
      BlankFragment2--->onAttach
      BlankFragment2--->onCreate
      BlankFragment1--->onHiddenChanged=true
      BlankFragment1--->onPause
      BlankFragment1--->onStop
      BlankFragment1--->onDestroyView
      BlankFragment2--->onViewCreated
      BlankFragment2--->onActivityCreated
      BlankFragment2--->onStart
      BlankFragment2--->onResume <<=================== 当前页
    • 锁屏
      lankFragment2--->onPause
      AddShowHideFragmentActivity--->onPause
      BlankFragment2--->onStop
      AddShowHideFragmentActivity--->onStop
      AddShowHideFragmentActivity--->onSaveInstanceState
    • 解锁屏幕
      AddShowHideFragmentActivity--->onRestart
      BlankFragment2--->onStart
      AddShowHideFragmentActivity--->onStart
      AddShowHideFragmentActivity--->onResume
      BlankFragment2--->onResume <<=================== 当前页
    • HOME回到桌面
      BlankFragment2--->onPause
      AddShowHideFragmentActivity--->onPause
      BlankFragment2--->onStop
      AddShowHideFragmentActivity--->onStop
      AddShowHideFragmentActivity--->onSaveInstanceState
    • 返回app页面
      AddShowHideFragmentActivity--->onRestart
      BlankFragment2--->onStart
      AddShowHideFragmentActivity--->onStart
      AddShowHideFragmentActivity--->onResume
      BlankFragment2--->onResume <<=================== 当前页
    • 跳转新页面
      BlankFragment2--->onPause
      AddShowHideFragmentActivity--->onPause
      MMKVActivity--->onCreate
      MMKVActivity--->onStart
      MMKVActivity--->onResume
      BlankFragment2--->onStop
      AddShowHideFragmentActivity--->onStop
      AddShowHideFragmentActivity--->onSaveInstanceState
    • 返回ViewPager的页面
      MMKVActivity--->onPause
      AddShowHideFragmentActivity--->onRestart
      BlankFragment2--->onStart
      AddShowHideFragmentActivity--->onStart
      AddShowHideFragmentActivity--->onResume
      BlankFragment2--->onResume <<=================== 当前页

    4) Fragment嵌套Fragment内的add show hide Fragment

    外层的activity只是add一个fragment

    /**
 * fragment内的viewpager内的fragment懒加载
 */
public class AddShowHideFragmentInFragmentActivity extends BindActivity implements AddFragmentInFragment.OnFragmentInteractionListener ,BlankFragment1.OnFragmentInteractionListener, BlankFragment2.OnFragmentInteractionListener, BlankFragment3.OnFragmentInteractionListener {

    @Override
    protected int setLayoutID() {
        return R.layout.activity_lazy_fragment;
    }

    @Override
    protected void initViews(Bundle savedInstanceState) {
        FragmentTransaction transaction=getSupportFragmentManager().beginTransaction();
        transaction.add(R.id.fl_content,AddFragmentInFragment.newInstance("",""));
        transaction.commit();
    }

    @Override
    public void onFragmentInteraction(Uri uri) {

    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
    }
}

    内部的fragment代码如下

    /**
 * add hide show显示的fragment 嵌套在 外层fragment内
 */
public class AddFragmentInFragment extends BaseFragment {

    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    private String mParam1;
    private String mParam2;

    private OnFragmentInteractionListener mListener;

    private static final String KEY_FRAGMENT_1 = "1";
    private static final String KEY_FRAGMENT_2 = "2";
    private static final String KEY_FRAGMENT_3 = "3";

    @BindView(R.id.tab_title)
    CommonTabLayout commonTabLayout;
    @BindView(R.id.tv_next)
    TextView tv_next;
    BlankFragment1 blankFragment1;
    BlankFragment2 blankFragment2;
    BlankFragment3 blankFragment3;
    List<Fragment> fragmentList;

    public AddFragmentInFragment() {
    }

    public static AddFragmentInFragment newInstance(String param1, String param2) {
        AddFragmentInFragment fragment = new AddFragmentInFragment();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public void onSaveInstanceState(@NonNull Bundle outState) {
        if(blankFragment1 != null&&blankFragment1.isAdded()) {
            mActivity.getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_1,blankFragment1);
        }
        if(blankFragment2 != null&&blankFragment2.isAdded()){
            mActivity.getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_2,blankFragment2);
        }
        if(blankFragment3 != null&&blankFragment3.isAdded()){
            mActivity.getSupportFragmentManager().putFragment(outState,KEY_FRAGMENT_3,blankFragment3);
        }
        super.onSaveInstanceState(outState);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }

    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        tv_next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(mContext, MMKVActivity.class);
                startActivity(intent);
            }
        });
        if(savedInstanceState != null){
            blankFragment1 = (BlankFragment1)mActivity.getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_1);
            blankFragment2 = (BlankFragment2)mActivity.getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_2);
            blankFragment3 = (BlankFragment3)mActivity.getSupportFragmentManager().getFragment(savedInstanceState,KEY_FRAGMENT_3);
        }
        fragmentList=new ArrayList<>();
        if (blankFragment1==null){
            fragmentList.add(blankFragment1=BlankFragment1.newInstance("11111",""));
        }else {
            fragmentList.add(blankFragment1);
        }
        if (blankFragment2==null){
            fragmentList.add(blankFragment2=BlankFragment2.newInstance("222222",""));
        }else {
            fragmentList.add(blankFragment2);
        }
        if (blankFragment3==null){
            fragmentList.add(blankFragment3=BlankFragment3.newInstance("3333333",""));
        }else {
            fragmentList.add(blankFragment3);
        }

        ArrayList<CustomTabEntity> tabEntities = new ArrayList<>();
        tabEntities.add(new TabLayoutEntity("商品1"));
        tabEntities.add(new TabLayoutEntity("评价2"));
        tabEntities.add(new TabLayoutEntity("详情3"));
        commonTabLayout.setTabData(tabEntities);
        commonTabLayout.setCurrentTab(0);
        showFragment(fragmentList.get(0),false);
        commonTabLayout.setOnTabSelectListener(new OnTabSelectListener() {
            @Override
            public void onTabSelect(int position) {
                showFragment(fragmentList.get(position),false);
            }

            @Override
            public void onTabReselect(int position) {
                showFragment(fragmentList.get(position),false);
            }
        });

    }

    private void showFragment(Fragment fragment,boolean replace){
        FragmentTransaction transaction = mActivity.getSupportFragmentManager().beginTransaction();
        if (replace){
            transaction.replace(R.id.fl_in_content,fragment);
        }else {
            if (!fragment.isAdded()){
                transaction.add(R.id.fl_in_content,fragment,fragment.getClass().getSimpleName());
            }
            hideAllFragment(transaction,fragment);
            transaction.show(fragment);
            transaction.setMaxLifecycle(fragment, Lifecycle.State.RESUMED);
        }
        transaction.commit();
    }
    private void hideAllFragment(FragmentTransaction transaction,Fragment withoutFragment){
        for (int i = 0; i < fragmentList.size(); i++) {
            if (!fragmentList.get(i).equals(withoutFragment)&&fragmentList.get(i).isAdded()){
                transaction.hide(fragmentList.get(i));
                transaction.setMaxLifecycle(fragmentList.get(i), Lifecycle.State.CREATED);
            }
        }
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_main, container, false);
    }

    public void onButtonPressed(Uri uri) {
        if (mListener != null) {
            mListener.onFragmentInteraction(uri);
        }
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof OnFragmentInteractionListener) {
            mListener = (OnFragmentInteractionListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement OnFragmentInteractionListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mListener = null;
    }

    public interface OnFragmentInteractionListener {
        void onFragmentInteraction(Uri uri);
    }
}

    实测日志可以发现，哪怕fragment是嵌套过的，Fragment的onResume生命周期也只会在当前页显示时调用：

    • 首次进入 显示第一页
      AddShowHideFragmentInFragmentActivity--->onCreate
      AddFragmentInFragment--->onAttach
      AddFragmentInFragment--->onCreate
      AddFragmentInFragment--->onViewCreated
      AddFragmentInFragment--->onActivityCreated
      BlankFragment1--->onAttach
      BlankFragment1--->onCreate
      BlankFragment1--->onViewCreated
      BlankFragment1--->onActivityCreated
      AddFragmentInFragment--->onStart
      BlankFragment1--->onStart
      AddShowHideFragmentInFragmentActivity--->onStart
      AddShowHideFragmentInFragmentActivity--->onResume
      AddFragmentInFragment--->onResume
      BlankFragment1--->onResume <<=================== 当前页
    • 点击显示第二页
      BlankFragment2--->onAttach
      BlankFragment2--->onCreate
      BlankFragment1--->onHiddenChanged=true
      BlankFragment1--->onPause
      BlankFragment1--->onStop
      BlankFragment1--->onDestroyView
      BlankFragment2--->onViewCreated
      BlankFragment2--->onActivityCreated
      BlankFragment2--->onStart
      BlankFragment2--->onResume <<=================== 当前页
    • 锁屏
      AddFragmentInFragment--->onPause
      BlankFragment2--->onPause
      AddShowHideFragmentInFragmentActivity--->onPause
      AddFragmentInFragment--->onStop
      BlankFragment2--->onStop
      AddShowHideFragmentInFragmentActivity--->onStop
      AddShowHideFragmentInFragmentActivity--->onSaveInstanceState
    • 解锁屏幕
      AddShowHideFragmentInFragmentActivity--->onRestart
      AddFragmentInFragment--->onStart
      BlankFragment2--->onStart
      AddShowHideFragmentInFragmentActivity--->onStart
      AddShowHideFragmentInFragmentActivity--->onResume
      AddFragmentInFragment--->onResume
      BlankFragment2--->onResume <<=================== 当前页
    • HOME回到桌面
      AddFragmentInFragment--->onPause
      BlankFragment2--->onPause
      AddShowHideFragmentInFragmentActivity--->onPause
      AddFragmentInFragment--->onStop
      BlankFragment2--->onStop
      AddShowHideFragmentInFragmentActivity--->onStop
      AddShowHideFragmentInFragmentActivity--->onSaveInstanceState
    • 返回app页面
      AddShowHideFragmentInFragmentActivity--->onRestart
      AddFragmentInFragment--->onStart
      BlankFragment2--->onStart
      AddShowHideFragmentInFragmentActivity--->onStart
      AddShowHideFragmentInFragmentActivity--->onResume
      AddFragmentInFragment--->onResume
      BlankFragment2--->onResume <<=================== 当前页
    • 跳转新页面
      AddFragmentInFragment--->onPause
      BlankFragment2--->onPause
      AddShowHideFragmentInFragmentActivity--->onPause
      MMKVActivity--->onCreate
      MMKVActivity--->onStart
      MMKVActivity--->onResume
      AddFragmentInFragment--->onStop
      BlankFragment2--->onStop
      AddShowHideFragmentInFragmentActivity--->onStop
      AddShowHideFragmentInFragmentActivity--->onSaveInstanceState
    • 返回当前页
      MMKVActivity--->onPause
      AddShowHideFragmentInFragmentActivity--->onRestart
      AddFragmentInFragment--->onStart
      BlankFragment2--->onStart
      AddShowHideFragmentInFragmentActivity--->onStart
      AddShowHideFragmentInFragmentActivity--->onResume
      AddFragmentInFragment--->onResume
      BlankFragment2--->onResume <<=================== 当前页

    三、小结

    上面列举了四种不同的使用场景，以及各种常见的操作逻辑，除了保证页面只有显示为当前页时才显示onResume生命周期函数外，也通过saveState方法解决了fragment销毁后，重叠显示的UI异常。
    希望上文对你有所帮助，顺便欢迎在上海的安卓开发，来我的Q群一起交流沟通开发与面试经验与互相内推，上海android互推面试 群号：465532338。

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