为什么 "dumpsys activity top" 在它的输出中列出 "fragment" 而我没有使用片段？

Question

SecondActivity只有简单的布局，在其onCreate()方法中设置为ContentView：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_second);
}

而 activity_second.xml 是：

<?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=".SecondActivity" />

但是当我使用dumpsys转储顶部activity时，它在输出中列出了一个未知的Fragment（"ReportFragment"）：

$ adb shell dumpsys activity top
TASK xxx.lifecycleapplication id=4
  ACTIVITY xxx.lifecycleapplication/.SecondActivity 538274ac pid=1519
    Local Activity 5368915c State:
      mResumed=true mStopped=false mFinished=false
      mLoadersStarted=true
      mChangingConfigurations=false
      mCurrentConfig={1.0 310mcc270mnc en_US sw384dp w384dp h567dp nrml port finger qwerty/v/v dpad/v s.5}
    Active Fragments in 536891f0:
      #0: ReportFragment{5369f99c #0 androidx.lifecycle.LifecycleDispatcher.report_fragment_tag}
        mFragmentId=#0 mContainerId=#0 mTag=androidx.lifecycle.LifecycleDispatcher.report_fragment_tag
        mState=5 mIndex=0 mWho=android:fragment:0 mBackStackNesting=0
        mAdded=true mRemoving=false mResumed=true mFromLayout=false mInLayout=false
        mHidden=false mDetached=false mMenuVisible=true mHasMenu=false
        mRetainInstance=false mRetaining=false mUserVisibleHint=true
        mFragmentManager=FragmentManager{536891f0 in SecondActivity{5368915c}}
        mActivity=xxx.lifecycleapplication.SecondActivity@5368915c
    Added Fragments:
      #0: ReportFragment{5369f99c #0 androidx.lifecycle.LifecycleDispatcher.report_fragment_tag}
    FragmentManager misc state:
      mCurState=5 mStateSaved=false mDestroyed=false
    Local FragmentActivity 5368915c State:
      mCreated=true mResumed=true mStopped=false    FragmentManager misc state:
      mHost=androidx.fragment.app.FragmentActivity$HostCallbacks@5368b814
      mContainer=androidx.fragment.app.FragmentActivity$HostCallbacks@5368b814
      mCurState=4 mStateSaved=false mStopped=false mDestroyed=false

为什么在 "Active Fragments" 和 "Added Fragments" 中输出显示 ReportFragment 而我没有使用任何 Fragment？

Answer 1

这一行就是线索：

mTag=androidx.lifecycle.LifecycleDispatcher.report_fragment_tag

ReportFragment is an implementation detail used by the lifecycle-process and the ProcessLifecycleOwner 用于跟踪您的应用是否已启动 activity。在 API 29 之前，它使用框架片段来跟踪所有活动（无论它们是 AppCompatActivity 还是常规 Activity 子类）。

为什么 "dumpsys activity top" 在它的输出中列出 "fragment" 而我没有使用片段？

Why does "dumpsys activity top" list "fragment" in its output while I did not use fragment?

android

adb

android-fragments

dumpsys