按下后退按钮后导航组件 currentDestination null
Navigation Component currentDestination null after pressing back-button
我已经使用导航组件 (v2.3.2) 实现了导航流程。当我第一次测试流程时,一切正常。但是,当我按下后退按钮返回到主片段并尝试再次测试流程时,应用程序崩溃了,因为 currentDestination 为空。当我按下后退按钮时,导航组件似乎卡住了。
错误:
java.lang.IllegalArgumentException: Navigation action/destination
com.tridie2000.myapp:id/action_fragmentA_to_fragmentB cannot be found
from the current destination
Destination(com.tridie2000.myapp:id/fragmentB) label=b_fragment
class=com.tridie2000.myapp.presentation.fragments.BFragment
这是我在 MainActivity 中配置导航组件的方式:
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
setupBottomNavBar()
setupNavigationUI()
}
override fun onCreateOptionsMenu(menu: Menu): Boolean {
val inflater: MenuInflater = menuInflater
inflater.inflate(R.menu.main_menu, menu)
return true
}
override fun onOptionsItemSelected(item: MenuItem): Boolean {
val navController = findNavController(R.id.nav_host_fragment)
return item.onNavDestinationSelected(navController) || super.onOptionsItemSelected(item)
}
private fun setupBottomNavBar() {
val navController = findNavController(R.id.nav_host_fragment)
val bottomNav = findViewById<BottomNavigationView>(R.id.bottom_navigation)
bottomNav.setupWithNavController(navController)
}
override fun onSupportNavigateUp(): Boolean {
val navController = findNavController(R.id.nav_host_fragment)
return navController.navigateUp()
}
private fun setupNavigationUI() {
val navController = findNavController(R.id.nav_host_fragment)
setupActionBarWithNavController(navController)
}
}
这是 MainActivity 的布局代码:
<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"
android:orientation="vertical"
tools:context=".presentation.activities.MainActivity">
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/bottom_navigation"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:background="@color/themeColor"
app:itemIconTint="@drawable/my_nav_bar_item_color"
app:itemTextColor="@drawable/my_nav_bar_item_color"
app:labelVisibilityMode="labeled"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:menu="@menu/main_tabbar_menu" />
<fragment
android:id="@+id/nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="0dp"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="@+id/bottom_navigation"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="@navigation/nav_graph"
tools:ignore="FragmentTagUsage" />
</androidx.constraintlayout.widget.ConstraintLayout>
好的,在进一步挖掘之后,我发现了我的应用程序崩溃的原因。在早期版本的导航组件中,错误是:
Action is unknown to this NavController
新错误(从 v2.3 开始)是:
Action/destination cannot be found from the current destination
当您连续多次执行 findNavController().navigate(action) 时会触发此事件。
我正在使用 RxJava,我的观察者被多次触发导致了这个错误。
修复我的 RxJava 实现后,我的导航流程工作正常。
我已经使用导航组件 (v2.3.2) 实现了导航流程。当我第一次测试流程时,一切正常。但是,当我按下后退按钮返回到主片段并尝试再次测试流程时,应用程序崩溃了,因为 currentDestination 为空。当我按下后退按钮时,导航组件似乎卡住了。
错误:
java.lang.IllegalArgumentException: Navigation action/destination com.tridie2000.myapp:id/action_fragmentA_to_fragmentB cannot be found from the current destination Destination(com.tridie2000.myapp:id/fragmentB) label=b_fragment class=com.tridie2000.myapp.presentation.fragments.BFragment
这是我在 MainActivity 中配置导航组件的方式:
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
setupBottomNavBar()
setupNavigationUI()
}
override fun onCreateOptionsMenu(menu: Menu): Boolean {
val inflater: MenuInflater = menuInflater
inflater.inflate(R.menu.main_menu, menu)
return true
}
override fun onOptionsItemSelected(item: MenuItem): Boolean {
val navController = findNavController(R.id.nav_host_fragment)
return item.onNavDestinationSelected(navController) || super.onOptionsItemSelected(item)
}
private fun setupBottomNavBar() {
val navController = findNavController(R.id.nav_host_fragment)
val bottomNav = findViewById<BottomNavigationView>(R.id.bottom_navigation)
bottomNav.setupWithNavController(navController)
}
override fun onSupportNavigateUp(): Boolean {
val navController = findNavController(R.id.nav_host_fragment)
return navController.navigateUp()
}
private fun setupNavigationUI() {
val navController = findNavController(R.id.nav_host_fragment)
setupActionBarWithNavController(navController)
}
}
这是 MainActivity 的布局代码:
<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"
android:orientation="vertical"
tools:context=".presentation.activities.MainActivity">
<com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/bottom_navigation"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:background="@color/themeColor"
app:itemIconTint="@drawable/my_nav_bar_item_color"
app:itemTextColor="@drawable/my_nav_bar_item_color"
app:labelVisibilityMode="labeled"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:menu="@menu/main_tabbar_menu" />
<fragment
android:id="@+id/nav_host_fragment"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="0dp"
android:layout_height="0dp"
app:defaultNavHost="true"
app:layout_constraintBottom_toTopOf="@+id/bottom_navigation"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="@navigation/nav_graph"
tools:ignore="FragmentTagUsage" />
</androidx.constraintlayout.widget.ConstraintLayout>
好的,在进一步挖掘之后,我发现了我的应用程序崩溃的原因。在早期版本的导航组件中,错误是:
Action is unknown to this NavController
新错误(从 v2.3 开始)是:
Action/destination cannot be found from the current destination
当您连续多次执行 findNavController().navigate(action) 时会触发此事件。
我正在使用 RxJava,我的观察者被多次触发导致了这个错误。
修复我的 RxJava 实现后,我的导航流程工作正常。