android - 后台管理 : Restarter must be created only during owner's initialization stage

Question

我在 MainActivity 中使用底部导航栏来处理一些 fragment 。这是用于在它们之间切换的代码:

private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
    if (item.isChecked &&
        supportFragmentManager.findFragmentById(R.id.act_main_fragment_container) != null
    )
        return@OnNavigationItemSelectedListener false
    val fragment =
        when (item.itemId) {
            R.id.navigation_home      -> fragments[0]
            R.id.navigation_bookings  -> fragments[1]
            R.id.navigation_messages  -> fragments[2]
            R.id.navigation_dashboard -> fragments[3]
            R.id.navigation_profile   -> fragments[4]
            else                      -> fragments[0]
        }
    this replaceWithNoBackStack fragment
    return@OnNavigationItemSelectedListener true
}

方法 replaceWithNoBackstack 只是一个简写:

supportFragmentManager
    ?.beginTransaction()
    ?.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
    ?.replace(containerId, fragment)
    ?.commit()

问题是当我在它们之间切换得更快时，我的应用程序崩溃并出现以下异常:

java.lang.IllegalStateException: Restarter must be created only during owner's initialization stage at androidx.savedstate.SavedStateRegistryController.performRestore(SavedStateRegistryController.java:59) at androidx.fragment.app.Fragment.performCreate(Fragment.java:2580) at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:837) at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1237) at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1302) at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439) at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2075) at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1865) at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1820) at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1726) at androidx.fragment.app.FragmentManagerImpl$2.run(FragmentManagerImpl.java:150) at android.os.Handler.handleCallback(Handler.java:789) at android.os.Handler.dispatchMessage(Handler.java:98) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6709) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769) I've been searching a lot and couldn't find an answer.

如果我执行 API 调用，将应用程序置于后台，等待响应，当我返回应用程序时，应用程序崩溃，因为我试图立即显示对话框 fragment ，我也会遇到此错误(我认为发生这种情况的原因是从后台返回时重新创建 fragment 的事务在显示对话框 fragment 时仍在进行中)。我通过为对话框设置 500 毫秒的延迟以一种 hacky 的方式解决了这个问题，因为我想不出其他解决方案。

请询问您是否需要有关此的更多详细信息。提前致谢!

可能的临时解决方案

编辑我通过将应用程序兼容性依赖项降级为 androidx.appcompat:appcompat:1.0.2 解决了这个问题，但这只是一个临时解决方案，因为我将来必须更新它。我希望有人能解决这个问题。

编辑 2我通过从 fragment 事务中删除 setTransition() 解决了这个问题。至少我知道为什么 android 应用程序通常没有很好的过渡

编辑 3也许避免此问题并使事情顺利进行的最佳解决方案就是使用 ViewPager 来处理底部栏导航

Answer 1

因为版本1.0.0没有检查状态，所以不会抛异常，但是版本1.1.0修改了源码，所以抛出异常。

这是Fragment version-1.1.0源码，会调用方法performRestore

    void performCreate(Bundle savedInstanceState) {
        if (mChildFragmentManager != null) {
            mChildFragmentManager.noteStateNotSaved();
        }
        mState = CREATED;
        mCalled = false;
        mSavedStateRegistryController.performRestore(savedInstanceState);
        onCreate(savedInstanceState);
        mIsCreated = true;
        if (!mCalled) {
            throw new SuperNotCalledException("Fragment " + this
                    + " did not call through to super.onCreate()");
        }
        mLifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_CREATE);
    }

/**
the exception
**/
public void performRestore(@Nullable Bundle savedState) {
        Lifecycle lifecycle = mOwner.getLifecycle();
        if (lifecycle.getCurrentState() != Lifecycle.State.INITIALIZED) {
            throw new IllegalStateException("Restarter must be created only during "
                    + "owner's initialization stage");
        }
        lifecycle.addObserver(new Recreator(mOwner));
        mRegistry.performRestore(lifecycle, savedState);
    }

这是1.0.0版本的源码，没有调用performRestore，所以不会抛异常

void performCreate(Bundle savedInstanceState) {
    if (mChildFragmentManager != null) {
        mChildFragmentManager.noteStateNotSaved();
    }
    mState = CREATED;
    mCalled = false;
    onCreate(savedInstanceState);
    mIsCreated = true;
    if (!mCalled) {
        throw new SuperNotCalledException("Fragment " + this
                + " did not call through to super.onCreate()");
    }
    mLifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_CREATE);
}

有两种不同的解决方案可以解决这个问题:
第一个解决方案是拆分事务。
因为我们总是使用replace或者将remove和add合并到一个Transaction中。我们可以像这样将事务拆分为两个事务:

FragmentTransaction ft = manager.beginTransaction();
        Fragment prev = manager.findFragmentByTag(tag);
        if (prev != null) {
        //commit immediately
            ft.remove(prev).commitAllowingStateLoss();
        }
        FragmentTransaction addTransaction = manager.beginTransaction();
        addTransaction.addToBackStack(null);
        addTransaction.add(layoutId, fragment,
                tag).commitAllowingStateLoss();

因为这两个事务将是两个不同的消息，将由 Handler 处理。
第二种解决方案是提前检查状态。我们可以按照源码，提前查看状态

FragmentTransaction ft = manager.beginTransaction();
        Fragment prev = manager.findFragmentByTag(tag);
        if (prev != null) {
        if (prev.getLifecycle().getCurrentState() != Lifecycle.State.INITIALIZED) {
            return;
        }
            ft.remove(prev);
        }

我推荐第一种方式，因为第二种方式是跟着源码走，如果源码代码更改代码，将无效。