2. 程式人生 > 程式設計 >androidx下的fragment的lazy懶載入問題詳解

androidx下的fragment的lazy懶載入問題詳解

阿新 • • 發佈：2020-04-17

網上關於androidx的fragment懶載入文章已經有很多，各有側重。幾乎都點到了sexMaxLifecycle和修改FragmentPagerAdapter。很少看到經過實踐的文章，謹以此文，更加詳盡的把實踐後的結果記錄下來，贈予有緣人。

一、前置準備工作

幾個關於androidx的fragment懶載入方案，都離不開如下幾個包：

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

我在實際測試程式碼中使用瞭如下版本，可供參考：

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

還準備了4個Activity與5個Fragment：

  • AddShowHideFragmentActivity 通過add show顯示的案例
  • AddShowHideFragmentInFragmentActivity 巢狀在fragment中的，通過add show顯示的fragment案例
  • ViewPagerFragmentActivity 通過ViewPager滑動顯示的案例
  • ViewPagerFragmentInFragmentActivity 巢狀在fragment中的，通過ViewPager滑動顯示的案例
  • AddFragmentInFragment 操作add show的fragment
  • ViewPagerFragmentInFragment 操作ViewPager的fragment
  • BlankFragment1 列印生命週期日誌的空頁面1
  • BlankFragment2 列印生命週期日誌的空頁面2
  • BlankFragment3 列印生命週期日誌的空頁面3

相應的幾個簡單佈局檔案:

檔案：fragment_main.xml

載入ViewPager控制元件和AddShow使用的FrameLayout，以及測試跳轉後返回的TextView按鈕。

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>

檔案：activity_lazy_fragment.xml

這裡是測試fragment巢狀情況下的佈局，fl_content用來載入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>

檔案：fragment_blank.xml

這一個空fragment就沒什麼講究了

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、具體程式碼分析

1) ViewPager+Fragment

最常見的使用方式，由ViewPager滑動顯示多個Fragment，直接上程式碼：

activity頁面程式碼

其中就是個簡單的viewpager設定adapter然後載入fragment集合顯示

/**
 * viewpager內的fragment懶載入
 */
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頁面程式碼

新版FragmentPagerAdapter多了2個常量

@Retention(RetentionPolicy.SOURCE)
  @IntDef({BEHAVIOR_SET_USER_VISIBLE_HINT,BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT})
  private @interface Behavior { }

用在了構造方法中

/**
   * 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;
  }

我們只需要在構造adapter時，使用BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT這個常量就行

/**
 * 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,fragmentTitleList,BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
  }
  public BaseFragmentXPagerAdapter(@NonNull FragmentManager fm,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,String[] fragmentTitleList,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;
    }
  }
}

最終列印生命週期日誌，確認結果，viewPager+fragment搭配pagerAdapter的behavior在各種情況下的日誌，可以看出新版viewPager+pagerAdapter實測下來，Fragment的onResume生命週期只會在當前頁顯示時呼叫：

首次進入 顯示第一頁
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 <<=================== 當前頁

滑動到第二頁
BlankFragment3--->onAttach
BlankFragment3--->onCreate
BlankFragment3--->onViewCreated
BlankFragment3--->onActivityCreated
BlankFragment3--->onStart
BlankFragment1--->onPause
BlankFragment2--->onResume <<=================== 當前頁

鎖屏
BlankFragment2--->onPause
ViewPagerFragmentActivity--->onPause
BlankFragment1--->onStop
BlankFragment2--->onStop
BlankFragment3--->onStop
ViewPagerFragmentActivity--->onStop
ViewPagerFragmentActivity--->onSaveInstanceState

解鎖螢幕
ViewPagerFragmentActivity--->onRestart
BlankFragment1--->onStart
BlankFragment2--->onStart
BlankFragment3--->onStart
ViewPagerFragmentActivity--->onStart
ViewPagerFragmentActivity--->onResume
BlankFragment2--->onResume <<=================== 當前頁

HOME回到桌面
BlankFragment2--->onPause
ViewPagerFragmentActivity--->onPause
BlankFragment1--->onStop
BlankFragment2--->onStop
BlankFragment3--->onStop
ViewPagerFragmentActivity--->onStop
ViewPagerFragmentActivity--->onSaveInstanceState

返回app頁面
ViewPagerFragmentActivity--->onRestart
BlankFragment1--->onStart
BlankFragment2--->onStart
BlankFragment3--->onStart
ViewPagerFragmentActivity--->onStart
ViewPagerFragmentActivity--->onResume
BlankFragment2--->onResume <<=================== 當前頁

跳轉新頁面
BlankFragment2--->onPause
ViewPagerFragmentActivity--->onPause
MMKVActivity--->onCreate
MMKVActivity--->onStart
MMKVActivity--->onResume
BlankFragment1--->onStop
BlankFragment2--->onStop
BlankFragment3--->onStop
ViewPagerFragmentActivity--->onStop
ViewPagerFragmentActivity--->onSaveInstanceState

返回ViewPager的頁面
MMKVActivity--->onPause
ViewPagerFragmentActivity--->onRestart
BlankFragment1--->onStart
BlankFragment2--->onStart
BlankFragment3--->onStart
ViewPagerFragmentActivity--->onStart
ViewPagerFragmentActivity--->onResume
BlankFragment2--->onResume <<=================== 當前頁
MMKVActivity--->onStop
MMKVActivity--->onDestroy

2) Fragment巢狀Fragment內的ViewPager+Fragment

外層的activity只是add一個fragment

/**
 * fragment內的viewpager內的fragment懶載入
 */
public class ViewPagerFragmentInFragmentActivity extends BindActivity implements ViewPagerFragmentInFragment.OnFragmentInteractionListener,BlankFragment1.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);
  }
}

巢狀用的fragment類，ViewPagerFragmentInFragment

/**
 * viewpager在一個fragment內
 */
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,blankFragment1);
    }
    if(blankFragment2 != null&&blankFragment2.isAdded()){
      mActivity.getSupportFragmentManager().putFragment(outState,blankFragment2);
    }
    if(blankFragment3 != null&&blankFragment3.isAdded()){
      mActivity.getSupportFragmentManager().putFragment(outState,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,""));
    }else {
      fragmentList.add(blankFragment3);
    }

    vp.setAdapter(new BaseFragmentXPagerAdapter(mActivity.getSupportFragmentManager(),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);
  }
}

實測日誌可以發現，哪怕fragment是巢狀過的，Fragment的onResume生命週期也只會在當前頁顯示時呼叫：

首次進入顯示第一頁
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 <<=================== 當前頁

滑動到第二頁
BlankFragment3--->onAttach
BlankFragment3--->onCreate
BlankFragment3--->onViewCreated
BlankFragment3--->onActivityCreated
BlankFragment3--->onStart
BlankFragment1--->onPause
BlankFragment2--->onResume <<=================== 當前頁

鎖屏
ViewPagerFragmentInFragment--->onPause
BlankFragment2--->onPause
ViewPagerFragmentInFragmentActivity--->onPause
ViewPagerFragmentInFragment--->onStop
BlankFragment1--->onStop
BlankFragment2--->onStop
BlankFragment3--->onStop
ViewPagerFragmentInFragmentActivity--->onStop
ViewPagerFragmentInFragmentActivity--->onSaveInstanceState

解鎖螢幕
ViewPagerFragmentInFragmentActivity--->onRestart
ViewPagerFragmentInFragment--->onStart
BlankFragment1--->onStart
BlankFragment2--->onStart
BlankFragment3--->onStart
ViewPagerFragmentInFragmentActivity--->onStart
ViewPagerFragmentInFragmentActivity--->onResume
ViewPagerFragmentInFragment--->onResume
BlankFragment2--->onResume <<=================== 當前頁

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頁面
ViewPagerFragmentInFragmentActivity--->onRestart
ViewPagerFragmentInFragment--->onStart
BlankFragment1--->onStart
BlankFragment2--->onStart
BlankFragment3--->onStart
ViewPagerFragmentInFragmentActivity--->onStart
ViewPagerFragmentInFragmentActivity--->onResume
ViewPagerFragmentInFragment--->onResume
BlankFragment2--->onResume <<=================== 當前頁

跳轉新頁面
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的頁面
MMKVActivity--->onPause
ViewPagerFragmentInFragmentActivity--->onRestart
ViewPagerFragmentInFragment--->onStart
BlankFragment1--->onStart
BlankFragment2--->onStart
BlankFragment3--->onStart
ViewPagerFragmentInFragmentActivity--->onStart
ViewPagerFragmentInFragmentActivity--->onResume
ViewPagerFragmentInFragment--->onResume
BlankFragment2--->onResume <<=================== 當前頁

3) 通過add show hide操作多個fragment

activity程式碼中的一個細節為通過add show的頁面，設定transaction.setMaxLifecycle(fragment,Lifecycle.State.RESUMED)，讓該fragment的生命週期能順利走到resume；

通過hide隱藏的頁面，設定transaction.setMaxLifecycle(fragmentList.get(i),Lifecycle.State.CREATED)，使隱藏了的fragment生命週期只能走到建立階段，無法走到resume方法。

/**
 * add show hide下的fragment懶載入
 */
public class AddShowHideFragmentActivity extends BindActivity implements BlankFragment1.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_3);
    }
    fragmentList=new ArrayList<>();
    if (blankFragment1==null){
      fragmentList.add(blankFragment1=BlankFragment1.newInstance("11111",""));
    }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("評價2"));
    tabEntities.add(new TabLayoutEntity("詳情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,blankFragment3);
    }
    super.onSaveInstanceState(outState);
  }
}

首次進入 顯示第一頁
AddShowHideFragmentActivity--->onCreate
BlankFragment1--->onAttach
BlankFragment1--->onCreate
BlankFragment1--->onViewCreated
BlankFragment1--->onActivityCreated
BlankFragment1--->onStart
AddShowHideFragmentActivity--->onStart
AddShowHideFragmentActivity--->onResume
BlankFragment1--->onResume <<=================== 當前頁

點選顯示第二頁
BlankFragment2--->onAttach
BlankFragment2--->onCreate
BlankFragment1--->onHiddenChanged=true
BlankFragment1--->onPause
BlankFragment1--->onStop
BlankFragment1--->onDestroyView
BlankFragment2--->onViewCreated
BlankFragment2--->onActivityCreated
BlankFragment2--->onStart
BlankFragment2--->onResume <<=================== 當前頁

鎖屏
lankFragment2--->onPause
AddShowHideFragmentActivity--->onPause
BlankFragment2--->onStop
AddShowHideFragmentActivity--->onStop
AddShowHideFragmentActivity--->onSaveInstanceState

解鎖螢幕
AddShowHideFragmentActivity--->onRestart
BlankFragment2--->onStart
AddShowHideFragmentActivity--->onStart
AddShowHideFragmentActivity--->onResume
BlankFragment2--->onResume <<=================== 當前頁

HOME回到桌面
BlankFragment2--->onPause
AddShowHideFragmentActivity--->onPause
BlankFragment2--->onStop
AddShowHideFragmentActivity--->onStop
AddShowHideFragmentActivity--->onSaveInstanceState

返回app頁面
AddShowHideFragmentActivity--->onRestart
BlankFragment2--->onStart
AddShowHideFragmentActivity--->onStart
AddShowHideFragmentActivity--->onResume
BlankFragment2--->onResume <<=================== 當前頁

跳轉新頁面
BlankFragment2--->onPause
AddShowHideFragmentActivity--->onPause
MMKVActivity--->onCreate
MMKVActivity--->onStart
MMKVActivity--->onResume
BlankFragment2--->onStop
AddShowHideFragmentActivity--->onStop
AddShowHideFragmentActivity--->onSaveInstanceState

返回ViewPager的頁面
MMKVActivity--->onPause
AddShowHideFragmentActivity--->onRestart
BlankFragment2--->onStart
AddShowHideFragmentActivity--->onStart
AddShowHideFragmentActivity--->onResume
BlankFragment2--->onResume <<=================== 當前頁

4) Fragment巢狀Fragment內的add show hide Fragment

外層的activity只是add一個fragment

/**
 * fragment內的viewpager內的fragment懶載入
 */
public class AddShowHideFragmentInFragmentActivity extends BindActivity implements AddFragmentInFragment.OnFragmentInteractionListener,AddFragmentInFragment.newInstance("",""));
    transaction.commit();
  }

  @Override
  public void onFragmentInteraction(Uri uri) {

  }

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

內部的fragment程式碼如下

/**
 * add hide show顯示的fragment 巢狀在 外層fragment內
 */
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,param2);
    fragment.setArguments(args);
    return fragment;
  }

  @Override
  public void onSaveInstanceState(@NonNull Bundle outState) {
    if(blankFragment1 != null&&blankFragment1.isAdded()) {
      mActivity.getSupportFragmentManager().putFragment(outState,MMKVActivity.class);
        startActivity(intent);
      }
    });
    if(savedInstanceState != null){
      blankFragment1 = (BlankFragment1)mActivity.getSupportFragmentManager().getFragment(savedInstanceState,""));
    }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("評價2"));
    tabEntities.add(new TabLayoutEntity("詳情3"));
    commonTabLayout.setTabData(tabEntities);
    commonTabLayout.setCurrentTab(0);
    showFragment(fragmentList.get(0),boolean replace){
    FragmentTransaction transaction = mActivity.getSupportFragmentManager().beginTransaction();
    if (replace){
      transaction.replace(R.id.fl_in_content,Lifecycle.State.CREATED);
      }
    }
  }

  @Override
  public View onCreateView(LayoutInflater inflater,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);
  }
}

實測日誌可以發現，哪怕fragment是巢狀過的，Fragment的onResume生命週期也只會在當前頁顯示時呼叫：

首次進入 顯示第一頁
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 <<=================== 當前頁

點選顯示第二頁
BlankFragment2--->onAttach
BlankFragment2--->onCreate
BlankFragment1--->onHiddenChanged=true
BlankFragment1--->onPause
BlankFragment1--->onStop
BlankFragment1--->onDestroyView
BlankFragment2--->onViewCreated
BlankFragment2--->onActivityCreated
BlankFragment2--->onStart
BlankFragment2--->onResume <<=================== 當前頁

鎖屏
AddFragmentInFragment--->onPause
BlankFragment2--->onPause
AddShowHideFragmentInFragmentActivity--->onPause
AddFragmentInFragment--->onStop
BlankFragment2--->onStop
AddShowHideFragmentInFragmentActivity--->onStop
AddShowHideFragmentInFragmentActivity--->onSaveInstanceState

解鎖螢幕
AddShowHideFragmentInFragmentActivity--->onRestart
AddFragmentInFragment--->onStart
BlankFragment2--->onStart
AddShowHideFragmentInFragmentActivity--->onStart
AddShowHideFragmentInFragmentActivity--->onResume
AddFragmentInFragment--->onResume
BlankFragment2--->onResume <<=================== 當前頁
HOME回到桌面
AddFragmentInFragment--->onPause
BlankFragment2--->onPause
AddShowHideFragmentInFragmentActivity--->onPause
AddFragmentInFragment--->onStop
BlankFragment2--->onStop
AddShowHideFragmentInFragmentActivity--->onStop
AddShowHideFragmentInFragmentActivity--->onSaveInstanceState

返回app頁面
AddShowHideFragmentInFragmentActivity--->onRestart
AddFragmentInFragment--->onStart
BlankFragment2--->onStart
AddShowHideFragmentInFragmentActivity--->onStart
AddShowHideFragmentInFragmentActivity--->onResume
AddFragmentInFragment--->onResume
BlankFragment2--->onResume <<=================== 當前頁

跳轉新頁面
AddFragmentInFragment--->onPause
BlankFragment2--->onPause
AddShowHideFragmentInFragmentActivity--->onPause
MMKVActivity--->onCreate
MMKVActivity--->onStart
MMKVActivity--->onResume
AddFragmentInFragment--->onStop
BlankFragment2--->onStop
AddShowHideFragmentInFragmentActivity--->onStop
AddShowHideFragmentInFragmentActivity--->onSaveInstanceState

返回當前頁
MMKVActivity--->onPause
AddShowHideFragmentInFragmentActivity--->onRestart
AddFragmentInFragment--->onStart
BlankFragment2--->onStart
AddShowHideFragmentInFragmentActivity--->onStart
AddShowHideFragmentInFragmentActivity--->onResume
AddFragmentInFragment--->onResume
BlankFragment2--->onResume <<=================== 當前頁

三、小結

上面列舉了四種不同的使用場景，以及各種常見的操作邏輯，除了保證頁面只有顯示為當前頁時才顯示onResume生命週期函式外，也通過saveState方法解決了fragment銷燬後，重疊顯示的UI異常。

到此這篇關於androidx下的fragment的lazy懶載入問題詳解的文章就介紹到這了,更多相關androidx fragment lazy懶載入內容請搜尋我們以前的文章或繼續瀏覽下面的相關文章希望大家以後多多支援我們！

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