背景是包含片段的活动：

override fun onCreate(savedInstanceState: Bundle?) {
        Log.d("===Activity: ","onCreate")
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        if (savedInstanceState == null) {
            supportFragmentManager.commit {
                add(R.id.main_cv, MainFragment())
                setReorderingAllowed(true)
                addToBackStack(null)
            }
        }
    }

然后我使用一些日志来观察这些生命周期回调的顺序，结果如下：

===Activity:: onCreate
===Activity:: onStart
===Fragment:: onAttach
===Fragment:: onCreate
===Fragment:: onCreateView
===Fragment:: onViewCreated
===Fragment:: onStart

我不知道为什么fragment.onCreate在activity.onStart之后调用而不是activity.onCreate。活动：

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        Log.d("===Activity: ","onCreate")
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        if (savedInstanceState == null) {
            supportFragmentManager.commit {
                add(R.id.main_cv, MainFragment())
                setReorderingAllowed(true)
                addToBackStack(null)
            }
        }
    }

    override fun onStart() {
        Log.d("===Activity: ","onStart")
        super.onStart()
    }

    override fun onResume() {
        Log.d("===Activity: ","onResume")
        super.onResume()
    }

    override fun onPause() {
        Log.d("===Activity: ","onPause")
        super.onPause()
    }

    override fun onStop() {
        Log.d("===Activity: ","onStop")
        super.onStop()
    }

    override fun onDestroy() {
        Log.d("===Activity: ","onDestroy")
        super.onDestroy()
    }
}

片段：

class MainFragment : Fragment() {

    override fun onAttach(context: Context) {
        Log.d("===Fragment: ","onAttach")
        super.onAttach(context)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        Log.d("===Fragment: ","onCreate")
        super.onCreate(savedInstanceState)
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        Log.d("===Fragment: ","onCreateView")
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_main, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        Log.d("===Fragment: ","onViewCreated")
        super.onViewCreated(view, savedInstanceState)
    }

    override fun onStart() {
        Log.d("===Fragment: ","onStart")
        super.onStart()
    }

    override fun onResume() {
        Log.d("===Fragment: ","onResume")
        super.onResume()
    }

    override fun onPause() {
        super.onPause()
        Log.d("===Fragment: ","onPause")
    }

    override fun onStop() {
        super.onStop()
        Log.d("===Fragment: ","onStop")
        
    }

    override fun onDestroyView() {
        super.onDestroyView()
        Log.d("===Fragment: ","onDestroyView")
    }

    override fun onDestroy() {
        super.onDestroy()
        Log.d("===Fragment: ","onDestroy")
    }
}