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。
