医生说:

有两种类型的标准pageradapter管理每个片段的生命周期:FragmentPagerAdapter和FragmentStatePagerAdapter。它们都能很好地处理片段，但它们更适合不同的场景:

The FragmentPagerAdapter stores the fragments in memory as long as the user can navigate between them. When a fragment is not visible, the PagerAdapter will detach it, but not destroy it, so the fragment instance remains alive in the FragmentManager. It will release it from memory only when the Activity shuts down. This can make the transition between pages fast and smooth, but it could cause memory issues in your app if you need many fragments. The FragmentStatePagerAdapter makes sure to destroy all the fragments the user does not see and only keep their saved states in the FragmentManager, hence the name. When the user navigates back to a fragment, it will restore it using the saved state. This PagerAdapter requires much less memory, but the process of switching between pages can be slower.

Like the docs say, think about it this way. If you were to do an application like a book reader, you will not want to load all the fragments into memory at once. You would like to load and destroy Fragments as the user reads. In this case you will use FragmentStatePagerAdapter. If you are just displaying 3 "tabs" that do not contain a lot of heavy data (like Bitmaps), then FragmentPagerAdapter might suit you well. Also, keep in mind that ViewPager by default will load 3 fragments into memory. The first Adapter you mention might destroy View hierarchy and re load it when needed, the second Adapter only saves the state of the Fragment and completely destroys it, if the user then comes back to that page, the state is retrieved.

医生说:

有两种类型的标准pageradapter管理每个片段的生命周期:FragmentPagerAdapter和FragmentStatePagerAdapter。它们都能很好地处理片段，但它们更适合不同的场景:

The FragmentPagerAdapter stores the fragments in memory as long as the user can navigate between them. When a fragment is not visible, the PagerAdapter will detach it, but not destroy it, so the fragment instance remains alive in the FragmentManager. It will release it from memory only when the Activity shuts down. This can make the transition between pages fast and smooth, but it could cause memory issues in your app if you need many fragments. The FragmentStatePagerAdapter makes sure to destroy all the fragments the user does not see and only keep their saved states in the FragmentManager, hence the name. When the user navigates back to a fragment, it will restore it using the saved state. This PagerAdapter requires much less memory, but the process of switching between pages can be slower.

FragmentStatePagerAdapter:

使用FragmentStatePagerAdapter，您不需要的片段是 摧毁。事务提交时完全删除 fragment从你的活动的FragmentManager。 FragmentStatePagerAdapter中的状态来自于它 将从savedInstanceState保存你的片段的Bundle什么时候 它被摧毁了。当用户导航回来时，新的片段将是 使用片段的状态恢复。

FragmentPagerAdapter:

相比之下，FragmentPagerAdapter什么也不做。当 不再需要这个片段。FragmentPagerAdapter调用 detach(Fragment)而不是remove(Fragment)。 这个destroy是片段的视图，但留下了片段的实例 在FragmentManager中存活。创建的片段 FragmentPagerAdapter永远不会被销毁。

下面是ViewPager中每个片段的日志生命周期，其中有4个片段，offscreenPageLimit = 1(默认值)

FragmentStatePagerAdapter

转到Fragment1(启动活动)

Fragment1: onCreateView
Fragment1: onStart
Fragment2: onCreateView
Fragment2: onStart

去Fragment2

Fragment3: onCreateView
Fragment3: onStart

进入Fragment3

Fragment1: onStop
Fragment1: onDestroyView
Fragment1: onDestroy
Fragment1: onDetach
Fragment4: onCreateView
Fragment4: onStart

去Fragment4

Fragment2: onStop
Fragment2: onDestroyView
Fragment2: onDestroy

FragmentPagerAdapter

转到Fragment1(启动活动)

Fragment1: onCreateView
Fragment1: onStart
Fragment2: onCreateView
Fragment2: onStart

去Fragment2

Fragment3: onCreateView
Fragment3: onStart

进入Fragment3

Fragment1: onStop
Fragment1: onDestroyView
Fragment4: onCreateView
Fragment4: onStart

去Fragment4

Fragment2: onStop
Fragment2: onDestroyView

结论:FragmentStatePagerAdapter在Fragment被offscreenPageLimit克服时调用onDestroy，而FragmentPagerAdapter没有。

注意:我认为我们应该使用FragmentStatePagerAdapter的ViewPager有很多页面，因为这将有利于性能。

offscreenPageLimit的示例:

如果我们转到Fragment3，它将破坏Fragment1(或者Fragment5)，因为offscreenPageLimit = 1。如果我们设置offscreenPageLimit > 1，它不会破坏。 如果在这个例子中，我们设置offscreenPageLimit=4，使用FragmentStatePagerAdapter和FragmentPagerAdapter之间没有区别，因为当我们改变制表符时，Fragment从不调用onDestroyView和onDestroy

Github演示在这里

FragmentPagerAdapter:用户访问的每个页面的片段将存储在内存中，尽管视图将被销毁。因此，当页面再次可见时，视图将被重新创建，但片段实例不会被重新创建。这可能会导致占用大量内存。当我们需要在内存中存储整个片段时，应该使用FragmentPagerAdapter。FragmentPagerAdapter在事务上调用detach(Fragment)而不是remove(Fragment)。

FragmentStatePagerAdapter:当片段实例对用户不可见时销毁，除了保存的片段状态。这导致只使用少量的内存，对于处理较大的数据集非常有用。当我们必须使用动态片段时应该使用，比如带有小部件的片段，因为它们的数据可以存储在savedInstanceState中。而且即使有大量的片段也不会影响性能。