Android ()-片段不能转换为androidx.navigation.fragment.NavHostFragment
Android ()-片段不能转换为androidx.navigation.fragment.NavHostFragment
提问于 2020-09-10 14:05:01
我决定为我的应用程序执行Firebase Robo测试，并注意到它总是在打开外部活动之后崩溃，然后返回到应用程序。通过启用开发人员选项中的“不要保持活动”，我能够复制这个问题。
崩溃：java.lang.ClassCastException: com.example.problemtesting.Fragments.Fragment_2 cannot be cast to androidx.navigation.fragment.NavHostFragment
它表明问题是由以下代码引起的：NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
如何重复这个问题：
- 启用“不要保留活动”
- 打开应用程序，然后打开应用程序抽屉
- 选择“片段2”
- 按共享按钮
- 按下“消息”按钮(或任何其他外部应用程序)
- 返回应用程序(崩溃)
如果“不要保持活动”被禁用，该应用程序可以正常工作。
MainActivity
public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener {
DrawerLayout drawer;
NavigationView navigationView;
FragmentManager fragmentManager;
AppBarConfiguration mAppBarConfiguration;
NavController navController;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fragmentManager = getSupportFragmentManager();
drawer = findViewById(R.id.drawer_layout);
navigationView = findViewById(R.id.nav_view);
// Passing each menu ID as a set of Ids because each
// menu should be considered as top level destinations.
mAppBarConfiguration = new AppBarConfiguration.Builder(
R.id.nav_fragment_1, R.id.nav_fragment_2)
.setOpenableLayout(drawer)
.build();
NavHostFragment navHostFragment = (NavHostFragment) getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment);
if (navHostFragment != null)
navController = navHostFragment.getNavController();
else navController = Navigation.findNavController(this, R.id.nav_host_fragment);
NavigationUI.setupActionBarWithNavController(MainActivity.this, navController, mAppBarConfiguration);
NavigationUI.setupWithNavController(navigationView, navController);
setNavigationViewListener();
}
@Override
public boolean onSupportNavigateUp() {
return NavigationUI.navigateUp(navController, mAppBarConfiguration)
|| super.onSupportNavigateUp();
}
private void setNavigationViewListener() {
navigationView.setNavigationItemSelectedListener(MainActivity.this);
}
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
switch (menuItem.getItemId()) {
case R.id.nav_fragment_1: {
fragmentManager.beginTransaction()
.replace(R.id.nav_host_fragment, new Fragment_1())
.commitNow();
MainActivity.this.setTitle("Fragment 1");
break;
}
case R.id.nav_fragment_2: {
fragmentManager.beginTransaction()
.replace(R.id.nav_host_fragment, new Fragment_2())
.commitNow();
MainActivity.this.setTitle("Fragment 2");
break;
}
}
drawer.closeDrawers();
return true;
}
}片段1
public class Fragment_1 extends Fragment{
public View onCreateView(@NonNull LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
container.removeAllViews();
View root = inflater.inflate(R.layout.fragment_1, container, false);
return root;
}
}片段2
public class Fragment_2 extends Fragment {
public View onCreateView(@NonNull LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
container.removeAllViews();
View root = inflater.inflate(R.layout.fragment_2, container, false);
Button share = root.findViewById(R.id.share);
share.setOnClickListener(view -> {
Intent intent = new Intent(Intent.ACTION_SEND);
intent.setType("text/plain");
intent.putExtra(Intent.EXTRA_SUBJECT, "Subject");
intent.putExtra(Intent.EXTRA_TEXT, "Message");
startActivity(Intent.createChooser(intent, "Title"));
});
return root;
}
}activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout 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/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start"
>
<androidx.fragment.app.FragmentContainerView
android:id="@+id/nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:tag="my_fragment"
android:layout_width="match_parent"
android:layout_height="0dp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintBottom_toBottomOf="parent"
app:defaultNavHost="true"
app:navGraph="@navigation/mobile_navigation"
/>
<com.google.android.material.navigation.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_main"
app:menu="@menu/main_drawer"
/>
</androidx.drawerlayout.widget.DrawerLayout>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"
app:startDestination="@+id/nav_fragment_1">
<fragment
android:id="@+id/nav_fragment_1"
android:name="com.example.problemtesting.Fragments.Fragment_1"
tools:layout="@layout/fragment_1"
/>
<fragment
android:id="@+id/nav_fragment_2"
android:name="com.example.problemtesting.Fragments.Fragment_2"
tools:layout="@layout/fragment_2"
/>
</navigation>main_drawer.xml
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
tools:showIn="navigation_view">
<group android:checkableBehavior="single">
<item
android:id="@+id/nav_fragment_1"
android:title="Fragment 1" />
<item
android:id="@+id/nav_fragment_2"
android:title="Fragment 2" />
</group>
</menu>AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.problemtesting">
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name="com.example.problemtesting.MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>我想不出这是个令人沮丧的问题。我试图删除NavigationView.OnNavigationItemSelectedListener侦听器，它运行良好，但我需要该侦听器用于其他控件，如片段切换动画和抽屉布局转换。
回答 1
Stack Overflow用户
回答已采纳
发布于 2020-09-10 15:35:23
问题是您的onNavigationItemSelected正在执行一个FragmentTransaction，将整个NavHostFragment替换为一个片段。在使用NavHostFragment时，这总是改变片段的错误方式--您应该始终是导航到目的地。
然而，在您的情况下，您所做的工作比实际需要的要多得多。相反，你应该：
- 完全删除
OnNavigationItemSelectedListener代码。当您调用NavigationUI.setupWithNavController(navigationView, navController);时，导航已经为您设置了一个，包括关闭抽屉和按照材料设计规范使用正确的交叉淡出动画。 - 根据顶部应用程序栏指南，您应该手动设置而不是，而是向图中的每个目标添加一个
android:label，您所做的setupActionBarWithNavController调用将为您做到这一点。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/63831423
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