这是我在片段中发现的重要信息:

Historically each screen in an Android app was implemented as a separate Activity. This creates a challenge in passing information between screens because the Android Intent mechanism does not allow passing a reference type (i.e. object) directly between Activities. Instead the object must be serialized or a globally accessible reference made available. By making each screen a separate Fragment, this data passing headache is completely avoided. Fragments always exist within the context of a given Activity and can always access that Activity. By storing the information of interest within the Activity, the Fragment for each screen can simply access the object reference through the Activity.

来源:https://www.pluralsight.com/blog/software-development/android-fragments

片段可以被认为是ui元素复合树中的非根组件，而活动位于复合树(ui树)的顶部。

A rule of thumb on when not to use Fragment is when as a child the fragment has a conflicting attribute, e.g., it may be immersive or may be using a different style all together or has some other architectural / logical difference and doesn't fit in the existing tree homogeneously. A rule of thumb on when to prefer Activity over Fragment is when the task (or set of coherent task) is fully independent and reusable and does some heavy weight lifting and should not be burdened further to conform to another parent-child composite (SRP violation, second responsibility would be to conform to the composite). For e.g., a MediaCaptureActivity that captures audio, video, photos etc and allows for edits, noise removal, annotations on photos etc and so on. This activity/module may have child fragments that do more granular work and conform to a common display theme.

不确定你指的是什么视频，但我怀疑他们说你应该使用片段而不是活动，因为它们不能直接互换。实际上，在开发指南中有一个相当详细的条目，考虑阅读它的详细信息。

In short, fragments live inside activities, and each activity can host many fragments. Like activities, they have a specific lifecycle, unlike activities, they are not top-level application components. Advantages of fragments include code reuse and modularity (e.g., using the same list view in many activities), including the ability to build multi-pane interfaces (mostly useful on tablets). The main disadvantage is (some) added complexity. You can generally achieve the same thing with (custom) views in a non-standard and less robust way.

如果你以前写过前端，那么使用前端组件(React, Vue或Angular)。将片段视为活动中的可重用组件。

#1 & #2使用片段的目的是什么 与使用片段相比，使用片段的优缺点 活动/视图/布局?

Fragments是Android用于创建可重用用户界面的解决方案。您可以使用活动和布局(例如使用include)来实现一些相同的功能。然而;fragments被连接到Android API中，从HoneyComb开始。让我详细说明;

The ActionBar. If you want tabs up there to navigate your app, you quickly see that ActionBar.TabListener interface gives you a FragmentTransaction as an input argument to the onTabSelected method. You could probably ignore this, and do something else and clever, but you'd be working against the API, not with it. The FragmentManager handles «back» for you in a very clever way. Back does not mean back to the last activity, like for regular activities. It means back to the previous fragment state. You can use the cool ViewPager with a FragmentPagerAdapter to create swipe interfaces. The FragmentPagerAdapter code is much cleaner than a regular adapter, and it controls instantiations of the individual fragments. Your life will be a lot easier if you use Fragments when you try to create applications for both phones and tablets. Since the fragments are so tied in with the Honeycomb+ APIs, you will want to use them on phones as well to reuse code. That's where the compatibility library comes in handy. You even could and should use fragments for apps meant for phones only. If you have portability in mind. I use ActionBarSherlock and the compatibility libraries to create "ICS looking" apps, that look the same all the way back to version 1.6. You get the latest features like the ActionBar, with tabs, overflow, split action bar, viewpager etc.

奖金2

片段之间最好的沟通方式是意图。当你在Fragment中按下一些东西时，你通常会调用StartActivity()，并在上面有数据。意图被传递到您启动的活动的所有片段。

片段存在于活动内部，而活动则独立存在。