问题

我有一个比较器屏幕，是一个分片的片段，分为2个子屏幕。在使用导航组件之前，我可以轻松地初始化片段：

private void initializeFragments() {

    FoodComparatorFragment comparatorFragment1 = new FoodComparatorFragment();
    FoodComparatorFragment comparatorFragment2 = new FoodComparatorFragment();

    FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
    transaction.add(R.id.comparator_fragment_1, comparatorFragment1);
    transaction.add(R.id.comparator_fragment_2, comparatorFragment2);

    transaction.commit();
}

但是，我不知道在不明确使用FragmentManager的情况下，应该如何执行此操作。

 private void initializeFragments() {

        FoodComparatorFragment comparatorFragment1 = new FoodComparatorFragment();
        FoodComparatorFragment comparatorFragment2 = new FoodComparatorFragment();

        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.add(R.id.comparator_fragment_1, comparatorFragment1);
        transaction.add(R.id.comparator_fragment_2, comparatorFragment2);

        transaction.commit();
    }

答案1

得分: 1

以下是已翻译的内容：

默认情况下，使用导航组件时，主活动（main activity）托管了一个NavHostFragment，适用于一种活动（activity）和多个片段（fragments）的模型。对于多个活动和片段的模型，每个活动都有自己的NavHostFragment和NavGraph。

在这里，我们将考虑一种活动和多个片段的模型，其中其中一个片段是比较器屏幕（父片段），分为2个子屏幕/片段。

但是，NavHostFragment一次只能托管一个片段；所以这里的想法是在比较器/父片段中有两个NavHostFragments。

考虑以下示例：

• 我们有一个托管两个片段（HomeFragment和ParentFragment）的MainActivity。
• ParentFragment是比较器，有两个NavHostFragments，每个都可以托管一个片段；顶部是TopFragment，底部是BottomFragment。
• 有一个从HomeFragment到ParentFragment的操作。
• 每个子屏幕都接收到一个int参数，即顶部和底部片段，通过将参数与从HomeFragment到ParentFragment的操作一起发送到子屏幕；它们将显示在屏幕上的TextViews上。

现在我们有3个NavGraphs：

主（mobile_navigation.xml）：

<?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/mobile_navigation"
    app:startDestination="@+id/navigation_home">

    <fragment
        android:id="@+id/navigation_home"
        android:name="com.example....HomeFragment"
        android:label="@string/title_home"
        tools:layout="@layout/fragment_home">

        <action
            android:id="@+id/action_homeFragment_to_parentFragment"
            app:destination="@id/navigation_parent"
            app:popUpTo="@id/navigation_home"
            app:popUpToInclusive="false" />

    </fragment>

    <fragment
        android:id="@+id/navigation_parent"
        android:name="com.example....ParentFragment"
        android:label="@string/title_parent"
        tools:layout="@layout/fragment_parent">

        <argument
            android:name="top_arg"
            android:defaultValue="-1"
            app:argType="integer" />

        <argument
            android:name="bottom_arg"
            android:defaultValue="-1"
            app:argType="integer" />

    </fragment>

</navigation>

在ParentFragment中，还有另外两个NavGraphs，分别用于子屏幕：

对于第一个子屏幕（top_navigation.xml）：

<?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/top_navigation"
    app:startDestination="@+id/top_fragment">

    <fragment
        android:id="@+id/top_fragment"
        android:name="com.example.....TopFragment"
        tools:layout="@layout/fragment_top">

        <argument
            android:name="arg"
            android:defaultValue="-1"
            app:argType="integer" />

    </fragment>

</navigation>

对于第二个子屏幕（bottom_navigation.xml）：

<?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/bottom_navigation"
    app:startDestination="@+id/bottom_fragment">

    <fragment
        android:id="@+id/bottom_fragment"
        android:name="com.example.....BottomFragment"
        tools:layout="@layout/fragment_bottom">

        <argument
            android:name="arg"
            android:defaultValue="-1"
            app:argType="integer" />

    </fragment>

</navigation>

布局（Layouts）：

activity_main.xml：

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/nav_host_fragment_activity_main"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/mobile_navigation" />

</androidx.constraintlayout.widget.ConstraintLayout>

fragment_parent.xml：

<androidx.constraintlayout.widget.ConstraintLayout 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="match_parent"
    tools:context=".ui.fragments.HomeFragment">

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/top_nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="@color/teal_200"
        app:layout_constraintBottom_toTopOf="@id/bottom_nav_host_fragment"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/bottom_nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="@color/purple_200"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraint

<details>
<summary>英文:</summary>

By default with navigation components there is one `NavHostFragment` hosted by the main activity for one activity/many fragments model. For many activities/fragments model, each activity has its own `NavHostFragment/NavGraph`.

Here we&#39;ll consider one activity, many fragments model, where one of these fragments is the Comparator Screen (parent fragment) that is splitted into 2 sub-screens/fragments.

But the `NavHostFragment` can only host a single fragment at a time; so the idea here is to have two `NavHostFragments` within the comparator/parent fragment.

-----

## Considering the below example:

 - We have a `MainActivity` that hosts two fragments (`HomeFragment`, `ParentFragment`).
 - The `ParentFragment` is the comparator with two `NavHostFragments`, each can host a single fragment; the top one is `TopFragment`, the bottom is `BottomFragment`.
 - There is an action to go from the `HomeFragment` to the `ParentFragment`
 - There is `int` argument sent to each sub-screen, the Top/Bottom fragments, done by sending arguments to the sub-screens along with the action from the `HomeFragment` to the `ParentFragment`; they will be displayed on `TextViews` on the screen.

MainActivity (1 NavHostFragments/NavGraph) ->> nav_host_fragment_activity_main
|
|---- HomeFragment
|
|---- ParentFragment (2 NavHostFragments/NavGraphs) ->> top_nav_host_fragment & bottom_nav_host_fragment
| |
| |---- TopFragment
| |
| |---- BottomFragment

### **Now we have 3 NavGraphs:**

Main (mobile_navigation.xml):

<?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/mobile_navigation"
app:startDestination="@+id/navigation_home">

<fragment
    android:id="@+id/navigation_home"
    android:name="com.example....HomeFragment"
    android:label="@string/title_home"
    tools:layout="@layout/fragment_home">

    <action
        android:id="@+id/action_homeFragment_to_parentFragment"
        app:destination="@id/navigation_parent"
        app:popUpTo="@id/navigation_home"
        app:popUpToInclusive="false" />

</fragment>

<fragment
    android:id="@+id/navigation_parent"
    android:name="com.example....ParentFragment"
    android:label="@string/title_parent"
    tools:layout="@layout/fragment_parent">

    <argument
        android:name="top_arg"
        android:defaultValue="-1"
        app:argType="integer" />

    <argument
        android:name="bottom_arg"
        android:defaultValue="-1"
        app:argType="integer" />

</fragment>

</navigation>

[![enter image description here][1]][1]

**And in `ParentFragment`, another two `NavGraphs`, each for a sub-screen:**

For the 1st sub-screen (top_navigation.xml):

<?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/top_navigation"
app:startDestination="@+id/top_fragment">

<fragment
    android:id="@+id/top_fragment"
    android:name="com.example.....TopFragment"
    tools:layout="@layout/fragment_top">

    <argument
        android:name="arg"
        android:defaultValue="-1"
        app:argType="integer" />

</fragment>

</navigation>

For the 2nd sub-screen (bottom_navigation.xml):

<?xml version="1.0" encoding="utf-8"?>
<navigation 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:id="@+id/bottom_navigation"
app:startDestination="@+id/bottom_fragment">

<fragment
    android:id="@+id/bottom_fragment"
    android:name="com.example.....BottomFragment"
    tools:layout="@layout/fragment_bottom">

    <argument
        android:name="arg"
        android:defaultValue="-1"
        app:argType="integer" />

</fragment>

</navigation>

**Layouts:**

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent">

<androidx.fragment.app.FragmentContainerView
    android:id="@+id/nav_host_fragment_activity_main"
    android:name="androidx.navigation.fragment.NavHostFragment"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:defaultNavHost="true"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:navGraph="@navigation/mobile_navigation" />

</androidx.constraintlayout.widget.ConstraintLayout>

fragment_parent.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="match_parent"
tools:context=".ui.fragments.HomeFragment">

<androidx.fragment.app.FragmentContainerView
    android:id="@+id/top_nav_host_fragment"
    android:name="androidx.navigation.fragment.NavHostFragment"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:background="@color/teal_200"
    app:layout_constraintBottom_toTopOf="@id/bottom_nav_host_fragment"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

<androidx.fragment.app.FragmentContainerView
    android:id="@+id/bottom_nav_host_fragment"
    android:name="androidx.navigation.fragment.NavHostFragment"
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:background="@color/purple_200"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/top_nav_host_fragment" />

</androidx.constraintlayout.widget.ConstraintLayout>

fragment_top/bottom.xml are straightforward 

fragment_top.xml:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="match_parent"
tools:context=".ui.fragments.ParentFragment">

<TextView
    android:id="@+id/textview"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:layout_marginEnd="8dp"
    android:textAlignment="center"
    android:text="top fragment"
    android:textSize="20sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

The `NavGraph` of the Top & Bottom fragments will be set programmatically in order to allow passing the arguments from the main `NavGraph` to the sub-screens' `NavGraphs`.

Now in the `HomeFragment`, there is a button to go to the `ParentFragment` with the action defined in the `NavGraph`, which sends the arguments needed for both sub-screens:

findNavController().navigate(
HomeFragmentDirections.actionHomeFragmentToParentFragment()
.setTopArg(100)
.setBottomArg(200))

Then receive the arguments at the `ParentFragment` with the `SafeArgs`:

// get fragment arguments through SafeArgs
val args = ParentFragmentArgs.fromBundle(requireArguments())
val bottomBundle = Bundle()
bottomBundle.putInt("arg", args.bottomArg)
val topBundle = Bundle()
topBundle.putInt("arg", args.topArg)
// setting the navGraph of the top/bottom NavHostFragments,
// and pass the argument along as a bundle.
val bottomNavHostFragment =
childFragmentManager.findFragmentById(R.id.bottom_nav_host_fragment)
as NavHostFragment
bottomNavHostFragment.navController.setGraph(R.navigation.bottom_navigation, bottomBundle)

val topNavHostFragment = childFragmentManager.findFragmentById(R.id.top_nav_host_fragment)
as NavHostFragment
topNavHostFragment.navController.setGraph(R.navigation.top_navigation, topBundle)

Once more at the destination top/bottom sub-screens, get the argument with `safeArgs`, and set it to the `TextView`:

// TopFragment
textView.text = TopFragmentArgs.fromBundle(
requireArguments()
).arg.toString()

// BottomFragment
textView.text = BottomFragmentArgs.fromBundle(
requireArguments()
).arg.toString()

[![enter image description here][2]][2]
 


  [1]: https://i.stack.imgur.com/pek44.png
  [2]: https://i.stack.imgur.com/Id25n.png

</details>