Android Navcontroller硬件后退按钮崩溃

Question

我正在使用新的Android故事板创建应用程序。流程需要如下：

  

SplashFragment-> Fragment1-> Fragment2

以下是情节提要（navigation_main.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/launch_navigation_graph"
            app:startDestination="@id/splashFragment">

    <fragment android:id="@+id/splashFragment" android:name="com.myapp.android.SplashFragment"
              android:label="fragment_splash" tools:layout="@layout/fragment_splash">
        <action android:id="@+id/action_splashFragment_to_fragment1"
                app:destination="@id/fragment1"/>
    </fragment>
    <fragment android:id="@+id/fragment1"
              android:name="com.myapp.android.Fragment1"
              android:label="fragment1" tools:layout="@layout/fragment_register_msisdn">
        <action android:id="@+id/action_fragment1_to_fragment2"
                app:destination="@id/fragment2" app:popUpTo="@+id/fragment1"
                app:enterAnim="@anim/nav_default_pop_enter_anim" app:exitAnim="@anim/nav_default_pop_exit_anim"/>
    </fragment>
    <fragment android:id="@+id/fragment2"
              android:name="com.myapp.android.Fragment2"
              android:label="fragment_fragment2" tools:layout="@layout/fragment_fragment2"/>
</navigation>

activity_main.xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="MainActivity">

    <fragment
            android:id="@+id/mainNavigationHostFragment"
            android:name="androidx.navigation.fragment.NavHostFragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:defaultNavHost="true"
            app:navGraph="@navigation/navigation_main" />

</androidx.constraintlayout.widget.ConstraintLayout>

应用主题没有操作栏，因为我不想显示操作栏：

<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">

基本上，我需要一个Fragment1到Fragment2导航，然后在按下硬件后退按钮时，返回到Fragment1。要从Fragment1导航到Fragment2，我在Fragment1中有以下代码：

findNavController().navigate(R.id.action_fragment1_to_fragment2)

SplashFragment不应保留在堆栈中，因为在首次启动时不需要。这就是为什么我只有popTo至Fragment1的行动中有Fragment2的原因。但是运行完相同内容后，从Fragment2向后按，则第一次不执行任何操作（不弹出），第二次由于以下异常而崩溃：

2019-04-25 16:52:43.841 28598-28598/com.selfcare.safaricom E/InputEventSender: Exception dispatching finished signal.
2019-04-25 16:52:43.842 28598-28598/com.selfcare.safaricom E/MessageQueue-JNI: Exception in MessageQueue callback: handleReceiveCallback
2019-04-25 16:52:43.846 28598-28598/com.selfcare.safaricom E/MessageQueue-JNI: java.lang.IllegalArgumentException: navigation destination com.selfcare.safaricom:id/action_splashFragment_to_registerMSISDNFragment is unknown to this NavController
        at androidx.navigation.NavController.navigate(NavController.java:803)
        at androidx.navigation.NavController.navigate(NavController.java:744)
        at androidx.navigation.NavController.navigate(NavController.java:730)
        at androidx.navigation.NavController.navigate(NavController.java:718)
        at com.myapp.android.SplashFragment.handleLaunchStatus(SplashFragment.kt:51)
        at com.myapp.android.SplashFragment.access$handleLaunchStatus(SplashFragment.kt:16)
        at com.myapp.android.SplashFragment$attachLaunchObserver$1.onChanged(SplashFragment.kt:44)
        at com.myapp.android.SplashFragment$attachLaunchObserver$1.onChanged(SplashFragment.kt:16)
        at androidx.lifecycle.LiveData.considerNotify(LiveData.java:113)
        at androidx.lifecycle.LiveData.dispatchingValue(LiveData.java:126)
        at androidx.lifecycle.LiveData$ObserverWrapper.activeStateChanged(LiveData.java:424)
        at androidx.lifecycle.LiveData$LifecycleBoundObserver.onStateChanged(LiveData.java:376)
        at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:361)
        at androidx.lifecycle.LifecycleRegistry.addObserver(LifecycleRegistry.java:188)
        at androidx.lifecycle.LiveData.observe(LiveData.java:185)
        at com.myapp.android.SplashFragment.attachLaunchObserver(SplashFragment.kt:43)
        at com.myapp.android.SplashFragment.onViewCreated(SplashFragment.kt:35)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:895)
        at androidx.fragment.app.FragmentManagerImpl.addAddedFragments(FragmentManagerImpl.java:2092)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1866)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1822)
        at androidx.fragment.app.FragmentManagerImpl.popBackStackImmediate(FragmentManagerImpl.java:298)
        at androidx.fragment.app.FragmentManagerImpl.popBackStackImmediate(FragmentManagerImpl.java:241)
        at androidx.fragment.app.FragmentManagerImpl.popBackStackImmediate(FragmentManagerImpl.java:288)
        at androidx.fragment.app.FragmentManagerImpl.popBackStackImmediate(FragmentManagerImpl.java:241)
        at androidx.fragment.app.FragmentActivity$1.handleOnBackPressed(FragmentActivity.java:144)
        at androidx.activity.OnBackPressedDispatcher.onBackPressed(OnBackPressedDispatcher.java:136)
        at androidx.activity.ComponentActivity.onBackPressed(ComponentActivity.java:283)
        at android.app.Activity.onKeyUp(Activity.java:3083)
        at android.view.KeyEvent.dispatch(KeyEvent.java:2716)
        at android.app.Activity.dispatchKeyEvent(Activity.java:3366)
        at androidx.core.app.ComponentActivity.superDispatchKeyEvent(ComponentActivity.java:80)
        at androidx.core.view.KeyEventDispatcher.dispatchKeyEvent(KeyEventDispatcher.java:84)
        at androidx.core.app.ComponentActivity.dispatchKeyEvent(ComponentActivity.java:98)
        at androidx.appcompat.app.AppCompatActivity.dispatchKeyEvent(AppCompatActivity.java:558)
        at androidx.appcompat.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:59)
        at androidx.appcompat.app.AppCompatDelegateImpl$AppCompatWindowCallback.dispatchKeyEvent(AppCompatDelegateImpl.java:2736)
        at com.android.internal.policy.DecorView.dispatchKeyEvent(DecorView.java:342)
        at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:5037)
        at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4905)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4426)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4479)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4445)
        at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4585)
        at android.view.ViewRootImpl$InputStage.apply(Vie
2019-04-25 16:52:43.849 28598-28598/com.selfcare.safaricom E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.selfcare.safaricom, PID: 28598
    java.lang.IllegalArgumentException: navigation destination com.selfcare.safaricom:id/action_splashFragment_to_registerMSISDNFragment is unknown to this NavController
        at androidx.navigation.NavController.navigate(NavController.java:803)
        at androidx.navigation.NavController.navigate(NavController.java:744)
        at androidx.navigation.NavController.navigate(NavController.java:730)
        at androidx.navigation.NavController.navigate(NavController.java:718)
        at com.myapp.android.SplashFragment.handleLaunchStatus(SplashFragment.kt:51)
        at com.myapp.android.SplashFragment.access$handleLaunchStatus(SplashFragment.kt:16)
        at com.myapp.android.SplashFragment$attachLaunchObserver$1.onChanged(SplashFragment.kt:44)
        at com.myapp.android.SplashFragment$attachLaunchObserver$1.onChanged(SplashFragment.kt:16)
        at androidx.lifecycle.LiveData.considerNotify(LiveData.java:113)
        at androidx.lifecycle.LiveData.dispatchingValue(LiveData.java:126)
        at androidx.lifecycle.LiveData$ObserverWrapper.activeStateChanged(LiveData.java:424)
        at androidx.lifecycle.LiveData$LifecycleBoundObserver.onStateChanged(LiveData.java:376)
        at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:361)
        at androidx.lifecycle.LifecycleRegistry.addObserver(LifecycleRegistry.java:188)
        at androidx.lifecycle.LiveData.observe(LiveData.java:185)
        at com.myapp.android.SplashFragment.attachLaunchObserver(SplashFragment.kt:43)
        at com.myapp.android.SplashFragment.onViewCreated(SplashFragment.kt:35)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:895)
        at androidx.fragment.app.FragmentManagerImpl.addAddedFragments(FragmentManagerImpl.java:2092)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1866)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1822)
        at androidx.fragment.app.FragmentManagerImpl.popBackStackImmediate(FragmentManagerImpl.java:298)
        at androidx.fragment.app.FragmentManagerImpl.popBackStackImmediate(FragmentManagerImpl.java:241)
        at androidx.fragment.app.FragmentManagerImpl.popBackStackImmediate(FragmentManagerImpl.java:288)
        at androidx.fragment.app.FragmentManagerImpl.popBackStackImmediate(FragmentManagerImpl.java:241)
        at androidx.fragment.app.FragmentActivity$1.handleOnBackPressed(FragmentActivity.java:144)
        at androidx.activity.OnBackPressedDispatcher.onBackPressed(OnBackPressedDispatcher.java:136)
        at androidx.activity.ComponentActivity.onBackPressed(ComponentActivity.java:283)
        at android.app.Activity.onKeyUp(Activity.java:3083)
        at android.view.KeyEvent.dispatch(KeyEvent.java:2716)
        at android.app.Activity.dispatchKeyEvent(Activity.java:3366)
        at androidx.core.app.ComponentActivity.superDispatchKeyEvent(ComponentActivity.java:80)
        at androidx.core.view.KeyEventDispatcher.dispatchKeyEvent(KeyEventDispatcher.java:84)
        at androidx.core.app.ComponentActivity.dispatchKeyEvent(ComponentActivity.java:98)
        at androidx.appcompat.app.AppCompatActivity.dispatchKeyEvent(AppCompatActivity.java:558)
        at androidx.appcompat.view.WindowCallbackWrapper.dispatchKeyEvent(WindowCallbackWrapper.java:59)
        at androidx.appcompat.app.AppCompatDelegateImpl$AppCompatWindowCallback.dispatchKeyEvent(AppCompatDelegateImpl.java:2736)
        at com.android.internal.policy.DecorView.dispatchKeyEvent(DecorView.java:342)
        at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:5037)
        at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4905)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4426)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4479)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4445)
2019-04-25 16:52:43.851 28598-28598/com.selfcare.safaricom E/AndroidRuntime:     at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4585)
        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4453)
        at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4642)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4426)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4479)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4445)
        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4453)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4426)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4479)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4445)
        at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4618)
        at android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent(ViewRootImpl.java:4779)
        at android.view.inputmethod.InputMethodManager$PendingEvent.run(InputMethodManager.java:2571)
        at android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback(InputMethodManager.java:2081)
        at android.view.inputmethod.InputMethodManager.finishedInputEvent(InputMethodManager.java:2072)
        at android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished(InputMethodManager.java:2548)
        at android.view.InputEventSender.dispatchInputEventFinished(InputEventSender.java:141)
        at android.os.MessageQueue.nativePollOnce(Native Method)
        at android.os.MessageQueue.next(MessageQueue.java:326)
        at android.os.Looper.loop(Looper.java:160)
        at android.app.ActivityThread.main(ActivityThread.java:6718)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

SplashFragment第51行是：

findNavController().navigate(R.id.action_splashFragment_to_fragment1)

如果我将popTo从Fragment1移至Fragment2操作，则此异常消失了，但是后退按钮也无法使用。我在这里做什么错了？

编辑1：

根据Stavro Xhardha的评论，我对导航XML进行了一些修改：

<fragment android:id="@+id/splashFragment" android:name="com.myapp.android.SplashFragment"
          android:label="fragment_splash" tools:layout="@layout/fragment_splash">
    <action android:id="@+id/action_splashFragment_to_fragment1"
            app:destination="@id/fragment1"
    app:popUpToInclusive="true" app:popUpTo="@+id/splashFragment"/> <!--Added this line -->
</fragment>
<fragment android:id="@+id/fragment1"
          android:name="com.myapp.android.Fragment1"
          android:label="fragment1" tools:layout="@layout/fragment_register_msisdn">
    <action android:id="@+id/action_fragment1_to_fragment2"
            app:destination="@id/fragment2" app:popUpTo="@+id/fragment1"/>
</fragment>
<fragment android:id="@+id/fragment2"
          android:name="com.myapp.android.Fragment2"
          android:label="fragment_fragment2" tools:layout="@layout/fragment_fragment2"/>

并在MainActivity中重写onBackPressed，如下所示：

override fun onBackPressed() {
    super.onBackPressed()
    if (!findNavController(R.id.launchNavigationHostFragment).navigateUp()) {
        finish()
    }
}

现在Fragment2会弹出到Fragment1，但是随后在Fragment1上按回键会继续使Fragment1处于循环状态。我无法退出该应用。

Answer 1

您的错误日志说您正在使用操作标识为action_splashFragment_to_registerMSISDNFragment的navcontroller调用操作。尝试找到该操作ID，并检查其是否有效。另外，请在{ name: "resolution", in: "query", required: true, type: "integer", format: "int32", enum: [ 1, 2, 3, 4 ] } 中使用app:popUpTo="@id/splashFragment" app:popUpToInclusive="true"而不是action_splashFragment_to_fragment1。这将从后堆栈中删除飞溅片段。这是代码段：

action_fragment1_to_fragment2

Answer 2

我终于设法解决了这个问题。

问题是，我正在观察MutableLiveData中的ViewModel，并根据其值进行导航。但是我不知道片段的生命周期所有者倾向于破坏Observer并根据视图生命周期对其进行实例化以避免泄漏。因此，一旦导航发生，观察者就不再在那里，并且要导航的代码在观察者之内。导航时需要相同的代码，因此当尝试访问它时，代码将崩溃。

我通过使用接口在需要完成导航时为片段提供回调来解决了这个问题。

Answer 3

导航到一个新片段后，我刚刚删除了观察者。就像这样：

myLiveData.removeObservers(this)