如何在fragmentActivity中检查片段是否可见?

我有 FragmentActivity 里面有4块碎片。 LoginFragment, RegistrationFragment, ForgottenPasswordFragment, LocalityFragment .

back button 在默认片段中( LoginFragment 或 LocalityFragment SplashScreen .

所以我找到了一些方法来获取当前显示的片段。我试过了 fragment.userVisibleHint fragment.isVisible . 当我按下后退按钮时,它们都返回false,即使该片段当前显示在屏幕上。

代码:

override fun onBackPressed() {
        val activeLoginFragment = supportFragmentManager.findFragmentByTag("LOGIN_FRAGMENT") as LoginFragment?
        val activeLocalityFragment = supportFragmentManager.findFragmentByTag("LOCALITY_FRAGMENT") as LocalityPickFragment?

        createLog("onBackPressedLogin ", activeLoginFragment.toString())
        createLog("onBackPressedLogin ", "LoginFragment is: " + activeLoginFragment?.userVisibleHint)
        if ( (activeLoginFragment == null || !activeLoginFragment.userVisibleHint) || (activeLocalityFragment == null || !activeLocalityFragment.userVisibleHint) ){
            createLog("onBackPressedLogin ", "not visible")
            super.onBackPressed()
        }

    }

fun switchToForgottenPasswordFragment(){
        val mPendingRunnable = Runnable {
            fragmentTransaction = supportFragmentManager.beginTransaction()
            fragmentTransaction.apply {
                replace(R.id.startup_fragment_container, forgottenPasswordFragment)
                addToBackStack(null)
                commit()
            }
        }

        val fragmentThread = Thread(mPendingRunnable)
        fragmentThread.start()
    }