Android 片段未保存 UI 按下后退按钮时的状态

Question

我运行我的用例有问题。它非常基本的用例。我有一个主要 activity 和 2 个片段。主要 activity 没有多少 UI。它所做的只是用 FirstFragment 替换它的容器。

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    if (savedInstanceState == null) {
        supportFragmentManager.beginTransaction()
                .replace(R.id.container, FirstFragment.newInstance())
            .addToBackStack(null)
                .commit()
    }
}

FirstFragment有2个按钮——initializeButton和button1，其中initializeButton默认处于启用状态，而button1只有在按下initializeButton后才启用。一旦在 initializeButton 之后按下 Button1，它就会启动 SecondFragment。以下是执行此操作的代码。

        requireActivity().supportFragmentManager.beginTransaction()
            .replace(R.id.container, SecondFragment.newInstance())
            .addToBackStack(null)
            .commit()

现在，这将正确启动 Secondfragment。现在，当我在 Fragment2 中按下后退按钮时，我想要的行为是启动第一个片段时两个按钮都处于启用状态。相反，它将进入第一个片段中的默认状态（在启用状态下初始化按钮，而在禁用状态下初始化按钮 1）。感谢任何反馈。谢谢

主要活动

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        if (savedInstanceState == null) {
            supportFragmentManager.beginTransaction()
                    .replace(R.id.container, FirstFragment.newInstance())
                .addToBackStack(null)
                    .commit()
        }
    }
}

MainActivity 布局

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" />

第一个片段

class FirstFragment : Fragment() {

    companion object {
        fun newInstance() = FirstFragment()
    }

    private lateinit var viewModel: SharedViewModel
    private lateinit var initializeButton: Button
    private lateinit var button1: Button
    private lateinit var newview: View

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

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        initializeButton = view.findViewById(R.id.button1)
        initializeButton.setOnClickListener{
            button1.isEnabled = true
        }
        button1 = view.findViewById(R.id.button2)
        button1.setOnClickListener{
            requireActivity().supportFragmentManager.beginTransaction()
                .replace(R.id.container, SecondFragment.newInstance())
                .addToBackStack(null)
                .commit()
        }
    }

    override fun onSaveInstanceState(outState: Bundle) {
        super.onSaveInstanceState(outState)
        outState.putBoolean("initState", initializeButton.isEnabled)
        outState.putBoolean("button1State", button1.isEnabled)
    }

    override fun onViewStateRestored(savedInstanceState: Bundle?) {
        super.onViewStateRestored(savedInstanceState)
        if (savedInstanceState != null) {
            initializeButton.isEnabled = savedInstanceState.getBoolean("initState")
            button1.isEnabled = savedInstanceState.getBoolean("button1State")
        }
    }

片段优先布局

<LinearLayout 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="wrap_content"
    tools:context=".FirstFragment">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:text="@string/initialize"
        android:enabled="true"
        android:layout_marginTop="5dp"/>

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toBottomOf="@id/button1"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:text="@string/button2"
        android:enabled="false"
        android:layout_marginTop="5dp"/>

    </androidx.constraintlayout.widget.ConstraintLayout>
</LinearLayout>

第二个片段

class SecondFragment : Fragment() {
    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_second, container, false)
    }

    companion object {
            fun newInstance() = SecondFragment()
    }
}

第二个片段布局

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/info"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="@string/second_fragment"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        android:textStyle="bold"
        android:visibility="visible"/>

    <ListView
        android:id="@+id/listView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

Answer 1

您更换片段有什么特别的原因吗？如果没有，您可以简单地添加它而不是替换它，这将确保状态得到维护。

你的代码会变成这样

   .add(R.id.container, SecondFragment.newInstance())
            .addToBackStack(null)
            .commit()

Android 片段未保存 UI 按下后退按钮时的状态

Android Fragment not saving UI State on pressing Back Button

android

android-layout

android-fragments

android-fragmentactivity