我有一个比较器屏幕,它是一个分为 2 个子屏幕的片段。在使用导航组件之前,我可以轻松地:
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,我不知道应该如何使用导航组件执行此操作而不显式使用
FragmentManager
。
默认情况下,导航组件有一个
NavHostFragment
由一个活动/多个片段模型的主活动托管。对于许多活动/片段模型,每个活动都有自己的NavHostFragment/NavGraph
。
在这里,我们将考虑一个活动,多个片段模型,其中这些片段之一是比较器屏幕(父片段),它被分成 2 个子屏幕/片段。
但是
NavHostFragment
一次只能承载一个片段;所以这里的想法是在比较器/父片段中有两个NavHostFragments
。
MainActivity
,其中包含两个片段(HomeFragment
、ParentFragment
)。ParentFragment
是具有两个NavHostFragments
的比较器,每个可以承载一个片段;上面的是TopFragment
,下面的是BottomFragment
。HomeFragment
到 ParentFragment
int
参数发送到每个子屏幕,即顶部/底部片段,通过将参数以及从 HomeFragment
到 ParentFragment
的操作发送到子屏幕来完成;它们将显示在屏幕上的 TextViews
上。MainActivity (1 NavHostFragments/NavGraph) ->> nav_host_fragment_activity_main
|
|---- HomeFragment
|
|---- ParentFragment (2 NavHostFragments/NavGraphs) ->> top_nav_host_fragment & bottom_nav_host_fragment
| |
| |---- TopFragment
| |
| |---- BottomFragment
主要(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,另外两个NavGraphs
,每个代表一个子屏幕:
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:
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 很简单
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>
顶部和底部片段的
NavGraph
将以编程方式设置,以便允许将参数从主 NavGraph
传递到子屏幕的 NavGraphs
。
现在在
HomeFragment
中,有一个按钮可以转到ParentFragment
,其操作在NavGraph
中定义,该操作发送两个子屏幕所需的参数:
findNavController().navigate(
HomeFragmentDirections.actionHomeFragmentToParentFragment()
.setTopArg(100)
.setBottomArg(200))
然后在
ParentFragment
处使用 SafeArgs
接收参数:
// 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)
再次在目标顶部/底部子屏幕上,使用
safeArgs
获取参数,并将其设置为 TextView
:
// TopFragment
textView.text = TopFragmentArgs.fromBundle(
requireArguments()
).arg.toString()
// BottomFragment
textView.text = BottomFragmentArgs.fromBundle(
requireArguments()
).arg.toString()