Question

我正在将ViewPager2与FragmentStateAdapter一起使用，并且正在调用notifyItemChanged（position）。但是按预期，createFragment方法不会再次调用。是预期的行为还是错误，我该怎么办

我的代码是

    class EEditionPagerAdapter(
    fragmentManager: FragmentManager, lifecycle: Lifecycle, private var date: String
    ) : FragmentStateAdapter(fragmentManager, lifecycle) {

    private var menuList = emptyList<EEditionMenu>()

    override fun getItemCount(): Int = menuList.size

    override fun createFragment(position: Int): Fragment {
        val menu = menuList[position]
        return EEditionListingFragment.newInstance(menu, date)
    }

    fun submitList(list: List<EEditionMenu>) {
        menuList = list
        notifyItemRangeChanged(0, menuList.size)
    }

    fun changeDate(date: String, position: Int){
        this.date = date
        notifyItemChanged(position)
    }
}

Answer 1

当您为FragmentStateAdapter调用notifyItemChanged时，它会调用ensureFragment(position)来恢复已创建的片段

 private void ensureFragment(int position) {
    long itemId = getItemId(position);
    if (!mFragments.containsKey(itemId)) {
        // TODO(133419201): check if a Fragment provided here is a new Fragment
        Fragment newFragment = createFragment(position);
        newFragment.setInitialSavedState(mSavedStates.get(itemId));
        mFragments.put(itemId, newFragment);
    }
}

尝试覆盖onBindViewHolder并将日期设置为片段

   override fun onBindViewHolder(
    holder: FragmentViewHolder,
    position: Int,
    payloads: MutableList<Any>
) {
    super.onBindViewHolder(holder, position, payloads)
    val fragment: EEditionListingFragment? = fragmentManager.findFragmentByTag("f$position") as EEditionListingFragment?
    fragment.updateDate(date)
}

Answer 2

FragmentStateAdapter使用项目ID来确定是否已创建片段，并重用已创建的片段。默认情况下，项目ID是项目的位置。您可以覆盖getItemId和containsItem以根据位置和日期提供自己的唯一ID，然后在日期更改时会要求一个新的片段。

Answer 3

放入FragementStateAdapter.class中的mFragment的片段由

管理

void placeFragmentInViewHolder(@NonNull final FragmentViewHolder holder)

方法，该方法是私有程序包，我们无权访问，在这种方法中，该片段被添加到标签为"f" + holder.getItemId()的mFragment管理器中，该标签与"f" + position相同。

        scheduleViewAttach(fragment, container);
        mFragmentManager.beginTransaction()
                .add(fragment, "f" + holder.getItemId())
                .setMaxLifecycle(fragment, STARTED)
                .commitNow();
        mFragmentMaxLifecycleEnforcer.updateFragmentMaxLifecycle(false);

因此，我们可以在显示碎片时覆盖onBindViewHolder方法。

@Override
public void onBindViewHolder(@NonNull FragmentViewHolder holder, int position, @NonNull List<Object> payloads) {
    super.onBindViewHolder(holder, position, payloads);
    if (position == 0) {

        String fragmentTag = "f" + holder.getItemId();
        Log.v(TAG,"fragmentTag is : " + fragmentTag);
        MyFragment fragment0 = (MyFragment) this.mFragmentManger.findFragmentByTag(fragmentTag);

        if (fragment0 != null) {
            Log.v(TAG,"onBindViewHolder updating fragment ...");
            // do what ever you want to update the MyFragment 
            fragment0.update(payloads);
        } else {
            Log.v(TAG,"onBindViewHolder called, but fragment0 is null!");
        }
    }
}

在我的情况下，this.mFragmentManager通过构造函数兑现。

public MyFragmentStateAdapter(@NonNull Fragment fragment) {
        super(fragment); // this calls the fragment.getChildFragmentManager().
        this.mFragmentManger = fragment.getChildFragmentManager();
}

createFragment()是：

@NonNull
@Override
public Fragment createFragment(int position) {
    if(position == 0){
        if (this.fragment0 == null) {
            this.fragment0 = MyFragment.getInstance();
        }
        return this.fragment0;
    } else {
        Log.v(TAG, "position " + position + " is called");
        return null;
    }
}

最后，在其他地方调用更新以触发更新：

ViewPager2.getAdapter().notifyItemChanged(0, null); 
// 0 is the fragment position of the fragment0 and null is payload.

ViewPager2的FragmentStateAdapter notifyItemChanged无法按预期工作

3 个答案: