旋转后无法恢复recyclerview滚动位置

Question

我制作了一个recyclerview网格，一旦用户按下按钮，它就会被api中的数据填满。旋转屏幕后，滚动位置会短暂恢复，然后再向上滚动到网格顶部。我使用本教程来保留我的滚动位置：

class MainActivity : AppCompatActivity(), Main.View {
    private lateinit var carAdapter: CarAdapter
    private lateinit var presenter: Main.MainPresenter
    private lateinit var cars: ArrayList<Car?>

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        carsAdapter = CarsAdapter(mutableListOf())
        // line suggested by androiddevelopers article
        carsAdapter.stateRestorationPolicy = 
        RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY

        gridRV.layoutManager = GridLayoutManager(this, 3)
        gridRV.adapter = carsAdapter
        if (savedInstanceState != null) {
            cars = savedInstanceState.getParcelableArrayList<Car?>(CARS_ARG)
                    as ArrayList<Car?>
            carsAdapter.cars = cars
            carsAdapter.notifyDataSetChanged()
        }
        presenter = Main.MainPresenter(this, CarService(R.string.api_ul))
        search_button.setOnClickListener { presenter.onSearchClick() } 
    }

    // presenter.onSearchClick() calls this
    override fun displayGrid() {
        this.cars = cars
        carsAdapter.cars = cars
        carsAdapter.notifyDataSetChanged()
    }

    override fun onSaveInstanceState(outState: Bundle) {
        super.onSaveInstanceState(outState)
        outState.putParcelableArrayList(CARS_ARG, cars)
    }
}

我还在本教程中尝试保存布局状态。

我的舱单条目是：

<activity
    android:name=".main.MainActivity"
    android:launchMode="singleTop">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

Answer 1

屏幕旋转是一种配置变化，它会导致活动重新创建，从而失去滚动的位置。

虽然你可以保存位置并恢复。

您还可以让您的活动忽略配置更改，这样它就不会重新创建。在清单中这样做：

<activity
    android:name=".main.MainActivity"
    android:configChanges="keyboardHidden|orientation|screenSize"
    android:launchMode="singleTop">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>