Fragment依附Activity生命周期问题
1.问题
一个Activity中有个Fragment，那启动Activity时Fragment和Activity的生命周期调用顺序时怎样的？
2.实践代码
MainActivity.kt
class MainActivity : AppCompatActivity() {
val TAG = "Test"
@SuppressLint("MissingInflatedId")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
Log.d(TAG,"Activity:onCreate 活动创建")
}
override fun onStart() {
super.onStart()
Log.d(TAG,"Activity:onStart 活动可见")
}
override fun onResume() {
super.onResume()
Log.d(TAG,"Activity:onResume 活动可交互")
}
override fun onRestart() {
super.onRestart()
Log.d(TAG,"Activity:onRestart 活动重新可见")
}
override fun onPause() {
super.onPause()
Log.d(TAG,"Activity:onPause 活动不可交互")
}
override fun onStop() {
super.onStop()
Log.d(TAG,"Activity:onStop 活动不可见")
}
override fun onDestroy() {
super.onDestroy()
Log.d(TAG,"Activity:onDestroy 活动状态销毁")
}
override fun onBackPressed() {
super.onBackPressed()
Log.d(TAG,"=======================================")
Log.d(TAG,"Activity:onBackPressed 主人按下返回键啦！！")
Log.d(TAG,"=======================================")
finish()
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<fragment
android:id="@+id/myFragment"
android:name="com.gxy.firstkotlinproject.MyFragment"
android:layout_width="200dp"
android:layout_height="200dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:layout="@layout/fragment_my"/>
</androidx.constraintlayout.widget.ConstraintLayout>
MyFragment.kt
class MyFragment : Fragment() {
val TAG = "Test"
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
Log.d(TAG, "Fragment:onCreate 碎片创建好啦！")
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_my, container, false)
}
companion object {
@JvmStatic
fun newInstance() =
MyFragment().apply {
}
}
override fun onAttach(context: Context) {
super.onAttach(context)
Log.d(TAG, "Fragment:onAttach 碎片依附到Activity中啦")
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
Log.d(TAG, "Fragment:onViewCreated 碎片视图创建成功")
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
Log.d(TAG, "Fragment:onActivityCreated 碎片和活动合体完成")
}
override fun onViewStateRestored(savedInstanceState: Bundle?) {
super.onViewStateRestored(savedInstanceState)
Log.d(TAG, "Fragment:onViewStateRestored ")
}
override fun onCreateAnimation(transit: Int, enter: Boolean, nextAnim: Int): Animation? {
Log.d(TAG, "Fragment:onCreateAnimation")
return super.onCreateAnimation(transit, enter, nextAnim)
}
override fun onCreateAnimator(transit: Int, enter: Boolean, nextAnim: Int): Animator? {
Log.d(TAG, "Fragment:onCreateAnimator")
return super.onCreateAnimator(transit, enter, nextAnim)
}
override fun onStart() {
super.onStart()
Log.d(TAG, "Fragment:onStart 碎片可见啦")
}
override fun onResume() {
super.onResume()
Log.d(TAG, "Fragment:onResume 碎片可以交互啦")
}
override fun onPause() {
super.onPause()
Log.d(TAG, "Fragment:onPause 碎片不能交互了")
}
override fun onStop() {
super.onStop()
Log.d(TAG, "Fragment:onStop 碎片不可见了")
}
override fun onDestroyView() {
super.onDestroyView()
Log.d(TAG, "Fragment:onDestroyView 碎片的布局被移除了")
}
override fun onDestroy() {
super.onDestroy()
Log.d(TAG, "Fragment:onDestroy 碎片的状态清理完毕")
}
override fun onDetach() {
super.onDetach()
Log.d(TAG, "Fragment:onDetach 碎片和活动撇清关系")
}
fragment_my.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/holo_blue_bright"
tools:context=".MyFragment">
<!-- TODO: Update blank fragment layout -->
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="@string/hello_blank_fragment" />
</FrameLayout>
启动结果截图：
正常按back键：
调用finish()销毁Activity：
- 过程分析：Fragment首先执行onAttach() 和Activity建立关联，然后开始创建onCreate()，再创建视图onViewCreated()
-> Activity正式创建成功onCreate()
-> Fragment 和Activity合体完成(都创建成功) onActivityCreated ，然后调用onViewStateRestored保存状态
-> Fragment 可见onStart()
-> Activity 可见 onStart()
-> Activity 可交互 onResume()
-> Fragment 可以交互 onResume()
- 按back键执行顺序是：
-> Fragment 不能交互了onPause
-> Activity 不可交互 onPause()
-> Fragment 不可见了 onStop()
-> Activity 不可见了 onStop()
- 如果活动销毁了，需要Fragment完全销毁，再销毁Activity：
Fragment 首先执行 onDestroyView() 把Fragment的布局移除了, 然后调用 onDestroy() 状态清理完毕, 然后和Activity撇清关系，解除关联
-> Activity 状态销毁onDestroy()
- Activity 创建的时候，Fragment一同创建，同时Fragment优先在后台先展示好，最后Activity带着Fragment一起展示到前台。
- emo版解释：Activity一直在等Fragment，直到他离开都还在等他走了才走，明明是Fragment先主动靠近、建立关系、创造回忆（关联onAttach、创建onCreate、创建视图onViewCreated），Activity才上头（创建onCreate） …… 离开的时候Fragment却头也不回，放弃回忆、清理痕迹、撇清关系（移除布局onDestroyView、状态清理onDestroy、解除关联onDetach），只剩Activity一人收拾残局（onDestroy）
内部源码解析请参考：https://blog.csdn.net/qq_29966203/article/details/124096543?spm=1001.2014.3001.5502