不推荐使用 FragmentPagerAdapter

因为 API 27FragmentPagerAdapter已经被废弃了。对于这个问题，最好的替代方案是什么？

在我的例子中，我理解需要使用像 super(fragmentManager, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT)这样的代码，但是我不知道在我的代码中需要使用哪些代码。

我班上有这些进口货:

import androidx.fragment.app.FragmentManager
import androidx.fragment.app.FragmentPagerAdapter

但是 class MyViewPagerAdapter(manager: FragmentManager) : FragmentPagerAdapter(manager){中的 FragmentPagerAdapter被划掉了。

class MyViewPagerAdapter(manager: FragmentManager) : FragmentPagerAdapter(manager){
private val fragmentList : MutableList<androidx.fragment.app.Fragment> = ArrayList()
private val titleList : MutableList<String> = ArrayList()


override fun getItem(position: Int): androidx.fragment.app.Fragment {
return fragmentList[position]
}


override fun getCount(): Int {
return fragmentList.size
}


fun addFragment(fragment: androidx.fragment.app.Fragment, title: String){
fragmentList.add(fragment)
titleList.add(title)
}


override fun getPageTitle(position: Int): CharSequence? {
return titleList[position]
}
}
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最佳答案

UPDATE 2021-06-14: At this point, ViewPager itself is all but deprecated. Technically, ViewPager is not deprecated, but the two concrete PagerAdapter implementations — FragmentPagerAdapter and FragmentStatePagerAdapter — are deprecated. Ideally, switch to something else, such as ViewPager2 or the pager composable in Accompanist.

Replace:

class MyViewPagerAdapter(manager: FragmentManager) : FragmentPagerAdapter(manager)

with:

class MyViewPagerAdapter(manager: FragmentManager) : FragmentPagerAdapter(manager, FragmentPagerAdapter.BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT)

(assuming that MyViewPagerAdapter does not need this value to be configurable)

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The javadocs actually has the following deprecation notice on FragmentPagerAdapter:

This class is deprecated.

Switch to ViewPager2 and use FragmentStateAdapter instead.

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It seems like not only the constructor without behavior, but the class FragmentPagerAdapter (which can consume a good amount of memory by keeping Fragments in memory), and FragmentStatePagerAdapter are both in deprecation stage. I wonder what can be used to extend abstract class PagerAdapter to extend codebase lifespan.

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Need to switch to ViewPager2, they have a migration guide here.

https://developer.android.com/training/animation/vp2-migration#java

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You can use FragmentStateAdapter(fragment)

class YourViewPagerAdapter(fragment: Fragment, val mFragmentList: Array<String>, val viewPager: ViewPager2) :  FragmentStateAdapter(fragment){


override fun getItemCount(): Int {
return mFragmentList.size
}


override fun createFragment(position: Int): Fragment {
when(position){
0 -> return YourFirstTabFragment()
1 -> return YourSecondTabFragment()
2 -> return YourThirdTabFragment()


}
return YourFirstTabFragment()
}




}
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Switch to ViewPager2 with FragmentStateAdapter.

Here is the XML view:-

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">


<com.google.android.material.tabs.TabLayout
android:id="@+id/tab_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content" />


<androidx.viewpager2.widget.ViewPager2
android:id="@+id/pager"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1" />


</LinearLayout>

class AdapterTabPager(activity: FragmentActivity?) : FragmentStateAdapter(activity!!) {
private val mFragmentList: MutableList<Fragment> = ArrayList()
private val mFragmentTitleList: MutableList<String> = ArrayList()
    

public fun getTabTitle(position : Int): String{
return mFragmentTitleList[position]
}


fun addFragment(fragment: Fragment, title: String) {
mFragmentList.add(fragment)
mFragmentTitleList.add(title)
}


override fun getItemCount(): Int {
return mFragmentList.size
}


override fun createFragment(position: Int): Fragment {
return mFragmentList[position]
}
}

Here is the way to instantiate ViewPager:-

val adapter = AdapterTabPager(activity)
adapter.addFragment(categoryFragment, "Category")
adapter.addFragment(brandFragment, "Brand")


rootView.viewpager.adapter = adapter
rootView.viewpager.currentItem = 0
TabLayoutMediator(rootView.tabs, rootView.viewpager) { tab, position ->
tab.text = adapter.getTabTitle(position)
}.attach()
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If you used this path New > Activities > Tabbed Activity so you need some changes:

1- XML

before

<androidx.viewpager.widget.ViewPager
android:id="@+id/view_pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:contentDescription="@string/pages"
app:layout_behavior="@string/appbar_scrolling_view_behavior" />

after

<androidx.viewpager2.widget.ViewPager2
android:id="@+id/view_pager"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:contentDescription="@string/pages"
app:layout_behavior="@string/appbar_scrolling_view_behavior" />

2- New Adapter As @Bharat Lalwani wrote below:

import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentActivity
import androidx.viewpager2.adapter.FragmentStateAdapter


class ScreenSlidePagerAdapter(activity: FragmentActivity?) : FragmentStateAdapter(activity!!) {
private val mFragmentList: MutableList<Fragment> = ArrayList()
private val mFragmentTitleList: MutableList<String> = ArrayList()


fun getTabTitle(position : Int): String{
return mFragmentTitleList[position]
}


fun addFragment(fragment: Fragment, title: String) {
mFragmentList.add(fragment)
mFragmentTitleList.add(title)
}


override fun getItemCount(): Int {
return mFragmentList.size
}


override fun createFragment(position: Int): Fragment {
return mFragmentList[position]
}
}

3- Main Activity

before

val sectionsPagerAdapter = SectionsPagerAdapter(this, supportFragmentManager)
val viewPager: ViewPager = binding.viewPager
viewPager.adapter = sectionsPagerAdapter
val tabs: TabLayout = binding.tabs
tabs.setupWithViewPager(viewPager)

after

val adapter = ScreenSlidePagerAdapter(this)


adapter.addFragment( PlaceholderFragment.newInstance( 1),"Brand")
adapter.addFragment( PlaceholderFragment.newInstance( 2),"Brand2")
val viewPager: ViewPager2 = binding.viewPager
viewPager.adapter = adapter
viewPager.currentItem = 0
val tabs: TabLayout = binding.tabs
TabLayoutMediator(tabs, viewPager) { tab, position ->
tab.text = adapter.getTabTitle(position)
}.attach()

4- Then you can delete SectionsPagerAdapter class


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