android - 尽管在 onDestroyView 中将父 View 设置为 null，但 fragment View 内存泄漏

Question

我知道将 fragment 事务添加到 backstack然后从那个 fragment 移动到另一个 fragment ，reference of the previous fragment's view is still available并且只有在按下后退按钮时才会被破坏。
为了避免这种情况，I have set the view to null in onDestroyView但问题是，leakcanary still shows view is not null and the view reference is still available而记录 View 说它是空的。

为什么会这样？
另外，如果我错了或遗漏了什么，请纠正我。

fragment 类-

private var mView: View? = null
private lateinit var btnSignUp: Button

 override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        mView = inflater.inflate(R.layout.fragment_login, container, false)
        return mView
    }

 override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        btnSignUp = view.findViewById(R.id.btnSignUp)

        btnSignUp.setOnClickListener {
            // calling function changeFragment()
            changeFragment(SignUpFragment(), FragmentsTag.SIGNUP_FRAGMENT)
        }
    }

override fun onDestroyView() {
        super.onDestroyView()      
         mView=null
    }

LeakCanary 分析日志 --

  HEAP ANALYSIS RESULT
    ====================================
    1 APPLICATION LEAKS

    References underlined with "~~~" are likely causes.
    Learn more at https://squ.re/leaks.

    43817 bytes retained by leaking objects
    Signature: 6e77557c8a679dd41391c1c5badaac98217366ad
    ┬───
    │ GC Root: System class
    │
    ├─ leakcanary.internal.InternalLeakCanary class
    │    Leaking: NO (MainActivity↓ is not leaking and a class is never leaking)
    │    ↓ static InternalLeakCanary.resumedActivity
    ├─ com.example.foodrunner.activities.MainActivity instance
    │    Leaking: NO (LoginFragment↓ is not leaking and Activity#mDestroyed is false)
    │    ↓ MainActivity.mFragments
    ├─ androidx.fragment.app.FragmentController instance
    │    Leaking: NO (LoginFragment↓ is not leaking)
    │    ↓ FragmentController.mHost
    ├─ androidx.fragment.app.FragmentActivity$HostCallbacks instance
    │    Leaking: NO (LoginFragment↓ is not leaking)
    │    ↓ FragmentActivity$HostCallbacks.mFragmentManager
    ├─ androidx.fragment.app.FragmentManagerImpl instance
    │    Leaking: NO (LoginFragment↓ is not leaking)
    │    ↓ FragmentManagerImpl.mActive
    ├─ java.util.HashMap instance
    │    Leaking: NO (LoginFragment↓ is not leaking)
    │    ↓ HashMap.table
    ├─ java.util.HashMap$HashMapEntry[] array
    │    Leaking: NO (LoginFragment↓ is not leaking)
    │    ↓ HashMap$HashMapEntry[].[0]
    ├─ java.util.HashMap$HashMapEntry instance
    │    Leaking: NO (LoginFragment↓ is not leaking)
    │    ↓ HashMap$HashMapEntry.value
    ├─ com.example.foodrunner.fragments.LoginFragment instance
    │    Leaking: NO (Fragment#mFragmentManager is not null)
    │    Fragment.mTag=Login Fragment
    │    ↓ LoginFragment.btnLogin
    │                    ~~~~~~~~
    ├─ com.google.android.material.button.MaterialButton instance
    │    Leaking: YES (View detached and has parent)
    │    mContext instance of com.example.foodrunner.activities.MainActivity with mDestroyed = false
    │    View#mParent is set
    │    View#mAttachInfo is null (view detached)
    │    View.mID = R.id.btnLogin
    │    View.mWindowAttachCount = 1
    │    ↓ MaterialButton.mParent
    ╰→ androidx.constraintlayout.widget.ConstraintLayout instance
    ​     Leaking: YES (ObjectWatcher was watching this because com.example.foodrunner.fragments.LoginFragment received Fragment#onDestroyView() callback (references to its views should be cleared to prevent leaks))
    ​     key = b72a82a6-b9dd-46c6-afb2-0ea6c7025001
    ​     watchDurationMillis = 9582
    ​     retainedDurationMillis = 4582
    ​     key = 0554b63a-c700-4c86-a451-b0daae06607a
    ​     watchDurationMillis = 9581
    ​     retainedDurationMillis = 4580
    ​     mContext instance of com.example.foodrunner.activities.MainActivity with mDestroyed = false
    ​     View#mParent is null
    ​     View#mAttachInfo is null (view detached)
    ​     View.mWindowAttachCount = 1
    ====================================

Answer 1

您仍然保留对 btnSignUp 的引用在 onDestroyView 之后- 那是什么泄漏。你必须放弃全部 引用 全部 刚刚被破坏的 View 中的 View 。

因此，您应该使用相同的方法(使其可以为空 var )或不保留对 btnSignUp 的引用完全在您的 Fragment 中-至少在您的代码示例中，它很容易成为局部变量。 (事实上​​，这同样适用于你的 mView - 你得到 View 作为 onViewCreated() 的输入，没有理由在 fragment 级别保留它)。