Android Navigation Component Not Displaying Fragme

问题:

I'm trying to implement the new Android Navigation Component in an existing app. I have 2 fragments that are identical except for their name. When I set the startDestination to fragment2, the fragment seems to be shown correctly. When the startDestination is set to fragment1, I don't see the inflated view but I do see the "Fragment 1 created" toast.

What am I doing incorrectly?

class Fragment1 : Fragment() {

  override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
      savedInstanceState: Bundle?): View? {
    Toast.makeText(context, "Fragment 1 created", Toast.LENGTH_LONG).show()
    return inflater.inflate(R.layout.fragment1, container, false)
  }

}

class Fragment2 : Fragment() {

  override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
      savedInstanceState: Bundle?): View? {
    Toast.makeText(context, "Fragment 2 created", Toast.LENGTH_LONG).show()
    return inflater.inflate(R.layout.fragment2, container, false)
  }


}

nav_graph.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/nav_graph"
    app:startDestination="@id/fragment1">

  <fragment
      android:id="@+id/fragment1"
      android:name="com.package.anotherpackage.ui.Fragment1"
      android:label="fragment1"
      tools:layout="@layout/fragment1"/>

  <fragment
      android:id="@+id/fragment2"
      android:name="com.package.anotherpackage.ui.Fragment2"
      android:label="fragment2"
      tools:layout="@layout/fragment2"/>
</navigation>

MainActivity layout:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    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"
    android:background="@android:color/background_light"
    tools:context=".MainActivity">

  <fragment
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:id="@+id/nav_host_fragment"
      android:name="androidx.navigation.fragment.NavHostFragment"
      app:navGraph="@navigation/nav_graph"
      app:defaultNavHost="true"
      app:layout_constraintBottom_toBottomOf="parent"
      app:layout_constraintEnd_toEndOf="parent"
      app:layout_constraintStart_toStartOf="parent"
      app:layout_constraintTop_toTopOf="parent"
      />

</FrameLayout>

Fragment1 Layout:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.Fragment1"
    >

  <!-- TODO: Update blank fragment layout -->
  <TextView
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:text="fragment 1"
      />

</FrameLayout>

Dependencies:

//Navigation
  def nav_version = "1.0.0-alpha05"

  implementation "android.arch.navigation:navigation-fragment-ktx:$nav_version"
  implementation "android.arch.navigation:navigation-ui-ktx:$nav_version"

  // optional - Test helpers
  androidTestImplementation "android.arch.navigation:navigation-testing-ktx:$nav_version"

回答1:

I had a layout in another library in my project with the name "fragment1.xml". It must have been conflicting with the other layout I was trying to inflate in Fragment1. Renaming the Fragment1 layout fixed the issue.