导航主机片段正在覆盖先前片段上的目标片段

Question

我正在尝试使用导航主机片段进行片段事务，但是在导航到目标片段时，旧片段仍然像在彼此上添加的片段一样在屏幕上可见。

这是我的代码：

settings_nav.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"
android:id="@+id/settings_nav"
app:startDestination="@+id/WelcomeFragment">

<fragment
    android:id="@+id/WelcomeFragment"
    android:name="com.example.ui.fragment.WelcomeFragment"
    android:label="WelcomeFragment">
    <action
        android:id="@+id/action_WelcomeFragment_to_secondFragment"
        app:destination="@+id/secondFragment"
         />
</fragment>

<fragment
    android:id="@+id/secondFragment"
    android:name="com.example.ui.fragment.ConfigFragment"
    android:label="secondFragment">
</fragment>

activity_main.xml

<fragment
    android:id="@+id/all_navigation_host_fragment"
    android:name="androidx.navigation.fragment.NavHostFragment"
    app:navGraph="@navigation/settings_nav"
    app:defaultNavHost="true"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@+id/toolbar"
    android:layout_gravity="top"
    tools:ignore="MergeRootFrame" />

WelcomeFragment.kt

button.setOnClickListener{
        findNavController().navigate(R.id.action_WelcomeFragment_to_secondFragment)
    }

MainActivity.kt

host = supportFragmentManager
        .findFragmentById(R.id.all_navigation_host_fragment) as NavHostFragment? ?: return
    navController = host.navController
    navController.addOnDestinationChangedListener { _, destination, _ ->
        val dest: String = try {
            resources.getResourceName(destination.id)
        } catch (e: Resources.NotFoundException) {
            Integer.toString(destination.id)
        }
        MALogger.d(TAG, "Navigated to $dest")
        var toolBarText = R.string.title
        when (destination.id) {
            R.id.WelcomeFragment -> toolBarText = R.string.title
            R.id.secondFragment -> toolBarText = R.string.button
        }
        setupToolbar(toolBarText)
    }

为什么要相互覆盖？我想念任何明显的东西吗？

Answer 1

这是因为您没有将选项添加到Pop up中，该选项会从后堆栈中弹出所有不匹配的目标，直到找到指定的目标为止。另外，您还需要添加popToInclusive选项，该选项还会从后堆栈中弹出指定的目标以及所有不匹配的目标。您的settings.xml应该如下所示：

<?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"
android:id="@+id/settings_nav"
app:startDestination="@+id/WelcomeFragment">

<fragment
    android:id="@+id/WelcomeFragment"
    android:name="com.example.ui.fragment.WelcomeFragment"
    android:label="WelcomeFragment">
    <action
        android:id="@+id/action_WelcomeFragment_to_secondFragment"
        app:destination="@+id/secondFragment"
        app:popUpTo="@id/WelcomeFragment"
        app:popUpToInclusive="true"
         />
</fragment>

<fragment
    android:id="@+id/secondFragment"
    android:name="com.example.ui.fragment.ConfigFragment"
    android:label="secondFragment">
</fragment>