android 停止FragmentPagerAdapter一次创建其所有片段

eeq64g8w  于 2024-01-04  发布在  Android
关注(0)|答案(3)|浏览(164)

所以我有一个底部导航栏，每个标签有4个片段，在每个片段中，我调用一个API请求来获取一些数据，但问题是每次我按下栏的任何标签，至少有两个片段被创建，它们调用自己的方法，并通过扩展触发API请求..！我只希望我选择的片段被示例化。
我知道适配器这样做是为了预先呈现片段，以确保在选项卡和诸如此类的东西之间进行更好的事务处理..！但我真的不能在每次选择时调用多个API调用..！

适配器

  1. public class My_PagerAdapter extends FragmentPagerAdapter {
  2.                        // I've tried FragmentStatePagerAdapter but same thing
  4.   public My_PagerAdapter (FragmentManager fm) {
  5.     super(fm);
  6.   }
  8.   @Override
  9.   public Fragment getItem(int position) {
  11.     switch (position) {
  12.       case 0:
  13.          new MyFragment_1();
  14.       case 1:
  15.          new MyFragment_2();
  16.       case 2:
  17.          new MyFragment_3();
  18.       case 3:
  19.          new MyFragment_4();
  20.     }
  22.   }
  24.   @Override
  25.   public int getCount() {
  26.     return 4;
  27.   }
  28. }

字符串

编辑

这就是我所谓的适配器。

  1. ViewPager viewPager = main.findViewById(R.id.vp); 
  2. viewPager.setOffscreenPageLimit(1); 
  3. viewPager.setAdapter(new My_PagerAdapter (getChildFragmentManager()));
  4. navigationTabBar.setModels(models); // just UI stuff for each tab offered by the bottom navigation bar library, 
  5. navigationTabBar.setViewPager(viewPager);

型

android

3条答案

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a11xaf1n

a11xaf1n1#

我在做一个项目的时候也遇到了同样的问题
我的解决方案是在每个片段中添加OnResume方法上的API调用。这样，只有当片段完全可见时，它们才会被触发。
查看fragment lifecycle

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yhxst69z

yhxst69z2#

好吧，这正是我面临的一个问题。我的解决方案并没有阻止viewpager创建片段，但它会停止对网络API的调用。
要点如下：
1)创建一个接口

  1. public interface ViewPagerLifeCycleManagerInterface {
  2.   void onResumeAndShowFragment();
  3.   void onPauseAndHideFragment();
  4.   //void refreshFragment();
  5. }

字符串
2)修改FragmentPagerAdapter以覆盖onInstantiateItem方法
在这里，每个Fragment都将在Adapter类中声明一个weakReference，以便存储对所创建的Fragment的引用

  1. @Override
  2. public Object instantiateItem(ViewGroup container, int position){
  4.     Fragment createdFragment = (Fragment) super.instantiateItem(container, position);
  6.     switch (position){
  7.         case 0:
  8.             xyzWeakReference=null;
  9.             xyzFragmentWeakReference=new WeakReference<>((xyz)createdFragment);
  10.             break;
  12.         case 1:
  13.             xyz1WeakReference=null;
  14.             xyz1WeakReference=new WeakReference<>((xyz1WeakReference)createdFragment);
  15.             break;
  17.     }
  19.     return createdFragment;
  20. };

型
3)在FragmentPagerAdapter中，添加以下方法以获取图片中片段的弱引用

  1. public Fragment getFragmentAtGivenPosition(int i){
  2.     switch (i){
  3.         case 0:
  4.             if(xyzFragmentWeakReference == null){
  5.                 return null;
  6.             }
  7.             return xyzFragmentWeakReference.get();
  8.         case 1:
  9.             if(xyz1FragmentWeakReference == null){
  10.                 return null;
  11.             }
  12.             return xyz1FragmentWeakReference.get();
  14.     }
  15. }

型
4)现在，在创建TabLayout并示例化视图页导航的Activity中，将侦听器附加到TabLayout以侦听选项卡更改

  1. tabLayout_bookmarks.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
  2.         @Override
  3.         public void onTabSelected(final TabLayout.Tab tab) {
  4.             //let the instantiateItem have some time to be called by the adapter
  6.             currentFragmentIndex = tab.getPosition();
  8.             new Handler().postDelayed(new Runnable() {
  9.                 @Override
  10.                 public void run() {
  12.                     ViewPagerLifeCycleManagerInterface currentFragment = (ViewPagerLifeCycleManagerInterface)btca.getFragmentAtGivenPosition(tab.getPosition());
  14.                     if(currentFragment!=null){
  15.                         currentFragment.onResumeAndShowFragment();
  16.                     }else{
  17.                         //Log.d("FragmentCreate","Current fragment is null and fucked up in adapter");
  19.                         //if it is null ... that means the adapter hasn't yet called instantiate item ... this internally calls get item any way
  20.                         //.....
  22.                         //This shouldn't really hit but in case it does ... keep a handler in order to ensure that everything is created
  23.                         new Handler().postDelayed(new Runnable() {
  24.                             @Override
  25.                             public void run() {
  26.                                 ViewPagerLifeCycleManagerInterface localFragment  = (ViewPagerLifeCycleManagerInterface)btca.getItem(tab.getPosition());
  27.                                 //getItem never returns a null fragment unless supplied a horrendous value for position
  28.                                 //by the time these 50 ms pass, the instantiate item should surely have been called
  29.                                 //else it will be an empty space ... no crash though
  30.                                 localFragment.onResumeAndShowFragment();
  31.                             }
  32.                         },50);
  33.                     }
  35.                 }
  36.             },100);
  38.         }
  40.         @Override
  41.         public void onTabUnselected(final TabLayout.Tab tab) {
  42.             new Handler().postDelayed(new Runnable() {
  43.                 @Override
  44.                 public void run() {
  45.                     ViewPagerLifeCycleManagerInterface currentFragment = (ViewPagerLifeCycleManagerInterface)btca.getFragmentAtGivenPosition(tab.getPosition());
  46.                     if(currentFragment!=null){
  47.                         currentFragment.onPauseAndHideFragment();
  48.                     }else{
  49.                         //Log.d("FragmentCreateTab","the fucking fragment was null");
  50.                         //if it is null ... that means the adapter hasn't yet called instantiate item ... this internally calls get item any way
  51.                         //.....
  53.                         //This shouldn't really hit but in case it does ... keep a handler in order to ensure that everything is created
  54.                         new Handler().postDelayed(new Runnable() {
  55.                             @Override
  56.                             public void run() {
  57.                                 ViewPagerLifeCycleManagerInterface localFragment  = (ViewPagerLifeCycleManagerInterface)btca.getItem(tab.getPosition());
  58.                                 //getItem never returns a null fragment unless supplied a horrendous value for position
  59.                                 //by the time these 50 ms pass, the instantiate item should surely have been called
  60.                                 //else it will be an empty space ... no crash though
  61.                                 localFragment.onPauseAndHideFragment();
  62.                             }
  63.                         },50);
  65.                     }
  67.                 }
  68.             },100);
  69.         }
  71.         @Override
  72.         public void onTabReselected(TabLayout.Tab tab) {
  73.             //do nothing
  74.         }
  75.     });

型
5)在Viewpager中的每个Fragment中，实现我们在步骤1中创建的Interface并覆盖方法。
在每个片段中创建一个布尔变量amIVisible.这将有助于决定片段何时可见以及何时可以调用网络API
a）这里对于viewpager中的第一个片段，即索引为0的片段，网络API调用必须在视图创建后立即发生。默认情况下，该片段显然是可见的。这是在oncodeView方法中编写的

  1. if(dataList!=null && dataList.size()==0) {
  2.         if (savedInstanceState==null) {
  3.             //your api call to load from net
  4.         } else {
  5.             if (savedInstanceState.getBoolean("savedState")) {
  6.                 //If you have saved data in state save, load it here
  7.             } else {
  8.                 //only fire the async if the current fragment is the one visible, else the onResumeAndShowFragment will trigger the same async when it becomes visible
  9.                 if (savedInstanceState.getBoolean("amIVisible")) {
  10.                     //Load data from net
  11.                 }
  12.             }
  13.         }
  14.     }

型
对于第一个片段，其他方法如下所示

  1. @Override
  2. public void onResumeAndShowFragment() {
  3.     amIVisible=true;
  5.     if(dataList!=null && dataList.size()==0){
  6.         new Handler().postDelayed(new Runnable() {
  7.             @Override
  8.             public void run() {
  9.                 //Load data from net if data was not found,
  10.                 //This basically means auto refresh when user scrolls back and the fragment had no data
  11.             }
  12.         },400);
  13.     }
  14. }
  16. @Override
  17. public void onPauseAndHideFragment() {
  18.     amIVisible=false;
  19. }

型
在这里，我已经覆盖了onSaveInstanceState方法，并保存了amIVisible的值，savedState是一个布尔值，表示列表是否至少有1个项目。
B）对于其他片段，数据将通过以下过程加载

  1. if(savedInstance!=null){
  3.         if (savedInstance.getBoolean("savedState")) {
  4.             new Handler().postDelayed(new Runnable() {
  5.                 @Override
  6.                 public void run() {
  7.                    //load data from saved State
  8.                 }
  9.             },100);
  11.         } else {
  12.             //only fire the async if the current fragment is the one visible, else the onResumeAndShowFragment will trigger the same async when it becomes visible
  14.             if (savedInstance.getBoolean("amIVisible")) {
  16.                 new Handler().postDelayed(new Runnable() {
  17.                     @Override
  18.                     public void run() {
  19.                         //load data from net
  20.                     }
  21.                 },100);
  23.             }
  24.         }
  25.     }

型
其他片段的接口方法相同。
这是相当复杂的，但做的工作。适配器内的弱引用甚至允许垃圾收集和避免上下文泄漏。

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ca1c2owp

ca1c2owp3#

防止加载视图页导航中的所有片段。
在视图分页器的setAdapret前添加此行. viewPager.setOffscreenPageLimit（number_of_fragment）; //示例：4
并检查登录onResume。可以更新其中的数据

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