androidx下的fragment的lazy懒加载问题详解

2023-07-27 02:41:13 74

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addshow显示的案例
AddShowHideFragmentInFragmentActivity嵌套在fragment中的，通过addshow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addshow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

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

文件：fragment_blank.xml

这一个空fragment就没什么讲究了

fragment_blank.xml

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
*/
publicclassViewPagerFragmentActivityextendsBindActivityimplementsBlankFragment1.OnFragmentInteractionListener,BlankFragment2.OnFragmentInteractionListener,BlankFragment3.OnFragmentInteractionListener{

privatestaticfinalStringKEY_FRAGMENT_1="1";
privatestaticfinalStringKEY_FRAGMENT_2="2";
privatestaticfinalStringKEY_FRAGMENT_3="3";
@BindView(R.id.vp_fragment)
ViewPagervp;
@BindView(R.id.tv_next)
TextViewtv_next;
BlankFragment1blankFragment1;
BlankFragment2blankFragment2;
BlankFragment3blankFragment3;
ListfragmentList;
@Override
protectedintsetLayoutID(){
returnR.layout.fragment_main;
}

@Override
protectedvoidinitViews(BundlesavedInstanceState){

tv_next.setOnClickListener(newView.OnClickListener(){
@Override
publicvoidonClick(Viewv){
Intentintent=newIntent(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=newArrayList<>();
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(newBaseFragmentXPagerAdapter(getSupportFragmentManager(),fragmentList,null));

}

@Override
publicvoidonFragmentInteraction(Uriuri){
}

@Override
protectedvoidonSaveInstanceState(BundleoutState){
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@interfaceBehavior{}

用在了构造方法中

/**
*Constructorfor{@linkFragmentPagerAdapter}.
*
*If{@link#BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT}ispassedin,thenonlythecurrent
*Fragmentisinthe{@linkLifecycle.State#RESUMED}state.Allotherfragmentsarecappedat
*{@linkLifecycle.State#STARTED}.If{@link#BEHAVIOR_SET_USER_VISIBLE_HINT}ispassed,all
*fragmentsareinthe{@linkLifecycle.State#RESUMED}stateandtherewillbecallbacksto
*{@linkFragment#setUserVisibleHint(boolean)}.
*
*@paramfmfragmentmanagerthatwillinteractwiththisadapter
*@parambehaviordeterminesifonlycurrentfragmentsareinaresumedstate
*/
publicFragmentPagerAdapter(@NonNullFragmentManagerfm,
@Behaviorintbehavior){
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

/**
*supportlazyinit
*/
publicclassBaseFragmentXPagerAdapterextendsFragmentPagerAdapter{

privateListmFragmentList=newArrayList<>();
privateListmFragmentTitleList=newArrayList<>();

publicBaseFragmentXPagerAdapter(@NonNullFragmentManagerfm,ListfragmentList,ListfragmentTitleList){
this(fm,fragmentList,fragmentTitleList,BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
}
publicBaseFragmentXPagerAdapter(@NonNullFragmentManagerfm,ListfragmentList,ListfragmentTitleList,intbehavior){
super(fm,behavior);
if(fragmentList!=null){
mFragmentList.addAll(fragmentList);
}
if(fragmentTitleList!=null){
mFragmentTitleList.addAll(fragmentTitleList);
}
}

publicBaseFragmentXPagerAdapter(@NonNullFragmentManagerfm,Fragment[]fragmentList,String[]fragmentTitleList){
this(fm,fragmentList,fragmentTitleList,BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
}
publicBaseFragmentXPagerAdapter(@NonNullFragmentManagerfm,Fragment[]fragmentList,String[]fragmentTitleList,intbehavior){
super(fm,behavior);
if(fragmentList!=null){
for(inti=0;i
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
*/
publicclassViewPagerFragmentInFragmentActivityextendsBindActivityimplementsViewPagerFragmentInFragment.OnFragmentInteractionListener,BlankFragment1.OnFragmentInteractionListener,BlankFragment2.OnFragmentInteractionListener,BlankFragment3.OnFragmentInteractionListener{

@Override
protectedintsetLayoutID(){
returnR.layout.activity_lazy_fragment;
}

@Override
protectedvoidinitViews(BundlesavedInstanceState){
FragmentTransactiontransaction=getSupportFragmentManager().beginTransaction();
transaction.add(R.id.fl_content,ViewPagerFragmentInFragment.newInstance("",""));
transaction.commit();
}

@Override
publicvoidonFragmentInteraction(Uriuri){

}

@Override
protectedvoidonSaveInstanceState(BundleoutState){
super.onSaveInstanceState(outState);
}
}


嵌套用的fragment类，ViewPagerFragmentInFragment
/**
*viewpager在一个fragment内
*/
publicclassViewPagerFragmentInFragmentextendsBaseFragment{
privatestaticfinalStringARG_PARAM1="param1";
privatestaticfinalStringARG_PARAM2="param2";

privateStringmParam1;
privateStringmParam2;

privateOnFragmentInteractionListenermListener;

privatestaticfinalStringKEY_FRAGMENT_1="1";
privatestaticfinalStringKEY_FRAGMENT_2="2";
privatestaticfinalStringKEY_FRAGMENT_3="3";

@BindView(R.id.vp_fragment)
ViewPagervp;
@BindView(R.id.tv_next)
TextViewtv_next;
BlankFragment1blankFragment1;
BlankFragment2blankFragment2;
BlankFragment3blankFragment3;
ListfragmentList;

publicViewPagerFragmentInFragment(){
}

publicstaticViewPagerFragmentInFragmentnewInstance(Stringparam1,Stringparam2){
ViewPagerFragmentInFragmentfragment=newViewPagerFragmentInFragment();
Bundleargs=newBundle();
args.putString(ARG_PARAM1,param1);
args.putString(ARG_PARAM2,param2);
fragment.setArguments(args);
returnfragment;
}

@Override
publicvoidonSaveInstanceState(@NonNullBundleoutState){

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
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
if(getArguments()!=null){
mParam1=getArguments().getString(ARG_PARAM1);
mParam2=getArguments().getString(ARG_PARAM2);
}

}

@Override
publicvoidonViewCreated(@NonNullViewview,@NullableBundlesavedInstanceState){
super.onViewCreated(view,savedInstanceState);
tv_next.setOnClickListener(newView.OnClickListener(){
@Override
publicvoidonClick(Viewv){
Intentintent=newIntent(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=newArrayList<>();
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(newBaseFragmentXPagerAdapter(mActivity.getSupportFragmentManager(),fragmentList,null));

}

@Override
publicViewonCreateView(LayoutInflaterinflater,ViewGroupcontainer,
BundlesavedInstanceState){
returninflater.inflate(R.layout.fragment_main,container,false);
}

publicvoidonButtonPressed(Uriuri){
if(mListener!=null){
mListener.onFragmentInteraction(uri);
}
}

@Override
publicvoidonAttach(Contextcontext){
super.onAttach(context);
if(contextinstanceofOnFragmentInteractionListener){
mListener=(OnFragmentInteractionListener)context;
}else{
thrownewRuntimeException(context.toString()
+"mustimplementOnFragmentInteractionListener");
}
}

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

publicinterfaceOnFragmentInteractionListener{
voidonFragmentInteraction(Uriuri);
}
}


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addshowhide操作多个fragment


activity代码中的一个细节为通过addshow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。
/**
*addshowhide下的fragment懒加载
*/
publicclassAddShowHideFragmentActivityextendsBindActivityimplementsBlankFragment1.OnFragmentInteractionListener,BlankFragment2.OnFragmentInteractionListener,BlankFragment3.OnFragmentInteractionListener{

privatestaticfinalStringKEY_FRAGMENT_1="1";
privatestaticfinalStringKEY_FRAGMENT_2="2";
privatestaticfinalStringKEY_FRAGMENT_3="3";
@BindView(R.id.tab_title)
CommonTabLayoutcommonTabLayout;
@BindView(R.id.tv_next)
TextViewtv_next;
BlankFragment1blankFragment1;
BlankFragment2blankFragment2;
BlankFragment3blankFragment3;
ListfragmentList;
@Override
protectedintsetLayoutID(){
returnR.layout.fragment_main;
}

@Override
protectedvoidinitViews(BundlesavedInstanceState){
tv_next.setOnClickListener(newView.OnClickListener(){
@Override
publicvoidonClick(Viewv){
Intentintent=newIntent(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=newArrayList<>();
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);
}
ArrayListtabEntities=newArrayList<>();
tabEntities.add(newTabLayoutEntity("商品1"));
tabEntities.add(newTabLayoutEntity("评价2"));
tabEntities.add(newTabLayoutEntity("详情3"));
commonTabLayout.setTabData(tabEntities);
commonTabLayout.setCurrentTab(0);
showFragment(fragmentList.get(0),false);
commonTabLayout.setOnTabSelectListener(newOnTabSelectListener(){
@Override
publicvoidonTabSelect(intposition){
showFragment(fragmentList.get(position),false);
}

@Override
publicvoidonTabReselect(intposition){
showFragment(fragmentList.get(position),false);
}
});

}

privatevoidshowFragment(Fragmentfragment,booleanreplace){
FragmentTransactiontransaction=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();
}
privatevoidhideAllFragment(FragmentTransactiontransaction,FragmentwithoutFragment){
for(inti=0;i
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addshowhideFragment


外层的activity只是add一个fragment
/**
*fragment内的viewpager内的fragment懒加载
*/
publicclassAddShowHideFragmentInFragmentActivityextendsBindActivityimplementsAddFragmentInFragment.OnFragmentInteractionListener,BlankFragment1.OnFragmentInteractionListener,BlankFragment2.OnFragmentInteractionListener,BlankFragment3.OnFragmentInteractionListener{

@Override
protectedintsetLayoutID(){
returnR.layout.activity_lazy_fragment;
}

@Override
protectedvoidinitViews(BundlesavedInstanceState){
FragmentTransactiontransaction=getSupportFragmentManager().beginTransaction();
transaction.add(R.id.fl_content,AddFragmentInFragment.newInstance("",""));
transaction.commit();
}

@Override
publicvoidonFragmentInteraction(Uriuri){

}

@Override
protectedvoidonSaveInstanceState(BundleoutState){
super.onSaveInstanceState(outState);
}
}
内部的fragment代码如下
/**
*addhideshow显示的fragment嵌套在外层fragment内
*/
publicclassAddFragmentInFragmentextendsBaseFragment{

privatestaticfinalStringARG_PARAM1="param1";
privatestaticfinalStringARG_PARAM2="param2";

privateStringmParam1;
privateStringmParam2;

privateOnFragmentInteractionListenermListener;

privatestaticfinalStringKEY_FRAGMENT_1="1";
privatestaticfinalStringKEY_FRAGMENT_2="2";
privatestaticfinalStringKEY_FRAGMENT_3="3";

@BindView(R.id.tab_title)
CommonTabLayoutcommonTabLayout;
@BindView(R.id.tv_next)
TextViewtv_next;
BlankFragment1blankFragment1;
BlankFragment2blankFragment2;
BlankFragment3blankFragment3;
ListfragmentList;

publicAddFragmentInFragment(){
}

publicstaticAddFragmentInFragmentnewInstance(Stringparam1,Stringparam2){
AddFragmentInFragmentfragment=newAddFragmentInFragment();
Bundleargs=newBundle();
args.putString(ARG_PARAM1,param1);
args.putString(ARG_PARAM2,param2);
fragment.setArguments(args);
returnfragment;
}

@Override
publicvoidonSaveInstanceState(@NonNullBundleoutState){
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
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
if(getArguments()!=null){
mParam1=getArguments().getString(ARG_PARAM1);
mParam2=getArguments().getString(ARG_PARAM2);
}

}

@Override
publicvoidonViewCreated(@NonNullViewview,@NullableBundlesavedInstanceState){
super.onViewCreated(view,savedInstanceState);
tv_next.setOnClickListener(newView.OnClickListener(){
@Override
publicvoidonClick(Viewv){
Intentintent=newIntent(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=newArrayList<>();
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);
}

ArrayListtabEntities=newArrayList<>();
tabEntities.add(newTabLayoutEntity("商品1"));
tabEntities.add(newTabLayoutEntity("评价2"));
tabEntities.add(newTabLayoutEntity("详情3"));
commonTabLayout.setTabData(tabEntities);
commonTabLayout.setCurrentTab(0);
showFragment(fragmentList.get(0),false);
commonTabLayout.setOnTabSelectListener(newOnTabSelectListener(){
@Override
publicvoidonTabSelect(intposition){
showFragment(fragmentList.get(position),false);
}

@Override
publicvoidonTabReselect(intposition){
showFragment(fragmentList.get(position),false);
}
});

}

privatevoidshowFragment(Fragmentfragment,booleanreplace){
FragmentTransactiontransaction=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();
}
privatevoidhideAllFragment(FragmentTransactiontransaction,FragmentwithoutFragment){
for(inti=0;i
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。


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androidx下的fragment的lazy懒加载问题详解

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