Android：没有通过app：startDestination为x.x.x：id / nav_graph定义的启动目标

Question

即使在使用nav_graph时，也会收到警告

项目级别gradle：

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    ext.kotlin_version = '1.3.72'
    repositories {
        google()
        jcenter()

    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.6.3'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        def nav_version = "2.3.0-beta01"
        classpath "androidx.navigation:navigation-safe-args-gradle-plugin:$nav_version"
    }
}

allprojects {
    repositories {
        google()
        jcenter()

    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

应用程序级别gradle：

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
apply plugin: "androidx.navigation.safeargs.kotlin"

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.3"

    defaultConfig {
        applicationId "com.demo.sample"
        minSdkVersion 16
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

    viewBinding {
        enabled = true
    }

}

dependencies {
    def nav_version = "2.3.0-beta01"
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.core:core-ktx:1.2.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
    // JetPack Navigation
    implementation "androidx.navigation:navigation-fragment-ktx:$nav_version"
    implementation "androidx.navigation:navigation-ui-ktx:$nav_version"
    implementation "androidx.navigation:navigation-dynamic-features-fragment:$nav_version"

}

MainActivity.kt

class MainActivity : AppCompatActivity() {

    //Binding reference
    private lateinit var binding : ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        initOnCreate()
    }

    /** Init OnCreate **/
    private fun initOnCreate() {
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

    }
}

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">
    <fragment
        android:id="@+id/frgChooseRecipient2"
        android:name="com.demo.sample.fragments.FrgChooseRecipient"
        android:label="fragment_choose_recipient"
        tools:layout="@layout/fragment_choose_recipient" >
        <action
            android:id="@+id/action_frgChooseRecipient2_to_frgConfirmation"
            app:destination="@id/frgConfirmation" />
    </fragment>
    <fragment
        android:id="@+id/frgViewTransaction2"
        android:name="com.demo.sample.fragments.FrgViewTransaction"
        android:label="fragment_view_transaction"
        tools:layout="@layout/fragment_view_transaction" />
    <fragment
        android:id="@+id/frgConfirmation"
        android:name="com.demo.sample.fragments.FrgConfirmation"
        android:label="fragment_confirmation"
        tools:layout="@layout/fragment_confirmation" />
    <fragment
        android:id="@+id/frgMain2"
        android:name="com.demo.sample.fragments.FrgMain"
        android:label="fragment_main"
        tools:layout="@layout/fragment_main" >
        <action
            android:id="@+id/action_frgMain2_to_frgSpecifyAmount"
            app:destination="@id/frgSpecifyAmount" />
        <action
            android:id="@+id/action_frgMain2_to_frgViewTransaction2"
            app:destination="@id/frgViewTransaction2" />
        <action
            android:id="@+id/action_frgMain2_to_frgBalance2"
            app:destination="@id/frgBalance2" />
    </fragment>
    <fragment
        android:id="@+id/frgSpecifyAmount"
        android:name="com.demo.sample.fragments.FrgSpecifyAmount"
        android:label="fragment_specify_amount"
        tools:layout="@layout/fragment_specify_amount" >
        <action
            android:id="@+id/action_frgSpecifyAmount_to_frgChooseRecipient2"
            app:destination="@id/frgChooseRecipient2" />
    </fragment>
    <fragment
        android:id="@+id/frgBalance2"
        android:name="com.demo.sample.fragments.FrgBalance"
        android:label="fragment_balance"
        tools:layout="@layout/fragment_balance" />
</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: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"
    tools:context=".activities.MainActivity">
    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/nav_graph" />
</androidx.constraintlayout.widget.ConstraintLayo

我面临的错误：

2020-05-30 23:19:57.486 17192-17192/com.demo.sample E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.demo.sample, PID: 17192
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.demo.sample/com.demo.sample.activities.MainActivity}: android.view.InflateException: Binary XML file line #8: Binary XML file line #8: Error inflating class androidx.fragment.app.FragmentContainerView
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: android.view.InflateException: Binary XML file line #8: Binary XML file line #8: Error inflating class androidx.fragment.app.FragmentContainerView
     Caused by: android.view.InflateException: Binary XML file line #8: Error inflating class androidx.fragment.app.FragmentContainerView
     Caused by: java.lang.IllegalStateException: no start destination defined via app:startDestination for com.demo.sample:id/nav_graph
        at androidx.navigation.NavGraphNavigator.navigate(NavGraphNavigator.java:61)
        at androidx.navigation.NavGraphNavigator.navigate(NavGraphNavigator.java:28)
        at androidx.navigation.NavController.navigate(NavController.java:1036)
        at androidx.navigation.NavController.onGraphCreated(NavController.java:629)
        at androidx.navigation.NavController.setGraph(NavController.java:586)
        at androidx.navigation.NavController.setGraph(NavController.java:551)
        at androidx.navigation.NavController.setGraph(NavController.java:533)
        at androidx.navigation.fragment.NavHostFragment.onCreate(NavHostFragment.java:238)
        at androidx.fragment.app.Fragment.performCreate(Fragment.java:2684)
        at androidx.fragment.app.FragmentStateManager.create(FragmentStateManager.java:280)
        at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1175)
        at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2224)
        at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1997)
        at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1953)
        at androidx.fragment.app.FragmentManager.execSingleAction(FragmentManager.java:1818)
        at androidx.fragment.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:303)
        at androidx.fragment.app.FragmentContainerView.<init>(FragmentContainerView.java:166)
        at androidx.fragment.app.FragmentLayoutInflaterFactory.onCreateView(FragmentLayoutInflaterFactory.java:51)
        at androidx.fragment.app.FragmentController.onCreateView(FragmentController.java:135)
        at androidx.fragment.app.FragmentActivity.dispatchFragmentsOnCreateView(FragmentActivity.java:356)
        at androidx.fragment.app.FragmentActivity.onCreateView(FragmentActivity.java:335)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:780)
        at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:730)
        at android.view.LayoutInflater.rInflate(LayoutInflater.java:863)
        at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:824)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
        at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
        at com.demo.sample.databinding.ActivityMainBinding.inflate(ActivityMainBinding.java:44)
        at com.demo.sample.databinding.ActivityMainBinding.inflate(ActivityMainBinding.java:38)
2020-05-30 23:19:57.488 17192-17192/com.demo.sample E/AndroidRuntime:     at com.demo.sample.activities.MainActivity.initOnCreate(MainActivity.kt:21)
        at com.demo.sample.activities.MainActivity.onCreate(MainActivity.kt:16)
        at android.app.Activity.performCreate(Activity.java:7136)
        at android.app.Activity.performCreate(Activity.java:7127)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

Answer 1

实际问题是

Caused by: java.lang.IllegalStateException: no start destination defined via app:startDestination for com.demo.sample:id/nav_graph

表示app:startDestination和navigation中提到的nav_graph.xml中的Designate a screen as the start destination标签没有设置Connect destinations属性。