Question

我有7个选项卡的Viewpager，就像在Play商店中，如果我们在主屏幕上点击选项卡，它将加载，如果再次点击该选项卡，它将不加载，我想如果我在选项卡1上点击，则应该加载，然后让在选项卡7上，然后我再次点击选项卡1，它不应加载，仅在满足某些条件时加载，我该怎么做？现在，它只是带有适配器的简单视图分页器，例如：

  public class PagerNewProductAdapter extends FragmentStatePagerAdapter { 
      RealmList<SubCategory> categoryData;
      String categoryName;
      String categoryId;
      Env env;

      public PagerNewProductAdapter(Fragment fragment, RealmList<SubCategory> category, String categoryName, String categoryId, Env env) {
        super(fragment.getChildFragmentManager());
        categoryData = category;
        this.categoryId = categoryId;
        this.env = env;
        this.categoryName = categoryName;
      }

      @Override
      public int getCount() {
        return categoryData.size() + 2;
      }

      @Override
      public Fragment getItem(int position) {
        Fragment fragment;
        if (position == 0) {
          fragment= ProductFragment.newInstance("2", categoryId, categoryName);
        } else if (position == 1) {
          fragment= ProductFragment.newInstance("3", categoryId, categoryName);
        } else {
          fragment= ProductFragment.newInstance("1", categoryData.get(position - 2).getCategoryId(), categoryName);
        }
        return fragment;
      }

      @Override
      public CharSequence getPageTitle(int position) {
        if (position == 0) {
          // return env.appSubcategoryViewAll;
          return env.appSubcategoryViewAll;
        } else if (position == 1) {
          return env.appDashboardCBrands;
        } else {
          return categoryData.get(position - 2).getName();
        }
     }
  }

谢谢

Answer 1

我认为在这种情况下，您可以使用SparseArray

public class PagerNewProductAdapter extends FragmentStatePagerAdapter {
  private final SparseArray<Fragment> registeredFragments = new SparseArray<>();
  RealmList<SubCategory> categoryData;
  String categoryName;
  String categoryId;
  Env env;

  public PagerNewProductAdapter(Fragment fragment, RealmList<SubCategory> category, String categoryName, String categoryId, Env env) {
    super(fragment.getChildFragmentManager());
    categoryData = category;
    this.categoryId = categoryId;
    this.env = env;
    this.categoryName = categoryName;
  }

  @NonNull
  @Override
  public Object instantiateItem(ViewGroup container, int position) {
    if (registeredFragments.get(position) == null) {
      Object fragment = super.instantiateItem(container, position);
      registeredFragments.put(position, (BaseFragment) fragment);
      return fragment;
    } else {
      return registeredFragments.get(position);
    }
  }

  @Override
  public void destroyItem(ViewGroup container, int position, Object object) {
    super.destroyItem(container, position, object);
    registeredFragments.remove(position);
  }

  @Override
  public Fragment getItem(int position) {
    Fragment fragment;
    if (position == 0) {
        fragment= ProductFragment.newInstance("2", categoryId, categoryName);
    } else if (position == 1) {
        fragment= ProductFragment.newInstance("3", categoryId, categoryName);
    } else {
        fragment= ProductFragment.newInstance("1", categoryData.get(position - 2).getCategoryId(), categoryName);
    }
    return fragment;
  }

  @Override
  public int getCount() {
    return categoryData.size() + 2;
  }



  @Override
  public CharSequence getPageTitle(int position) {
    if (position == 0) {
       // return env.appSubcategoryViewAll;
        return env.appSubcategoryViewAll;
    } else if (position == 1) {
        return env.appDashboardCBrands;
    } else {
        return categoryData.get(position - 2).getName();
    }
  }
}

Answer 2

像这样简单地添加setOffscreenPageLimit：

    viewPager = findViewById(R.id.viewpager);
    viewPager.setOffscreenPageLimit(3);

3 = viewpager中的片段数。

Answer 3

我认为您需要使用Fragmentation。它按照您的要求工作。如果您有任何疑问，请告诉我。

步骤1：实施碎片化https://github.com/YoKeyword/Fragmentation

步骤2：从SupportActivity而不是AppCompatActivity扩展您的活动从SupportFragment扩展片段而不是Fragment

步骤3：从片段中删除onresume和onpause方法

第4步：调用onPause（）;在onViewCreated方法中

@Override
    public void onSupportVisible() {
        super.onSupportVisible();
       onResume();
        if(!isLoaded){
            isLoaded = true;
//Load your data here 
}
}
@Override
    public void onSupportInvisible() {
        super.onSupportInvisible();
       onPause();
    }

第5步：设置setlimit viewPager.setOffscreenPageLimit（numberi）;

快乐编码。

Answer 4

您可以将先前创建的片段存储在数组中。这样可以确保如果数组中存在以前创建的实例，我们将使用它。

public class PagerNewProductAdapter extends FragmentStatePagerAdapter { 
      Fragment[] cache;
      RealmList<SubCategory> categoryData;
      ...

      public PagerNewProductAdapter(Fragment fragment, RealmList<SubCategory> category, String categoryName, String categoryId, Env env) {
        ...
        this.categoryName = categoryName;
        this.cache = new Fragment[getCount()];
      }

      @Override
      public int getCount() {
        return categoryData.size() + 2;
      }

      @Override
      public Fragment getItem(int position) {

        Fragment cachedFragment = cache[position]
        if(cachedFragment == null){
            if (position == 0) {
                cache[position] = ProductFragment.newInstance("2", categoryId, categoryName);
                cachedFragment = cache[position];
            } else if (position == 1) {
                cache[position] = ProductFragment.newInstance("3", categoryId, categoryName);
                cachedFragment = cache[position];
            } else {
                cache[position]= ProductFragment.newInstance("1", categoryData.get(position - 2).getCategoryId(), categoryName);
                cachedFragment = cache[position];
            }
        }
        return cachedFragment;
      }
      ...
  }

如果页面已经加载，如何使viewpager不再加载页面

4 个答案: