Question

我正在使用Jetpack Navigation来处理Fragments的导航。在关注文档后，当我运行应用程序时，我收到以下错误。

Caused by: java.lang.ClassNotFoundException: Didn't find class "androidx.navigation.fragment.NavHostFragment"

的build.gradle

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
apply plugin: 'kotlin-kapt'

android {
compileSdkVersion 'android-P'

defaultConfig {
    applicationId "com.meditab.imspatient"
    minSdkVersion 21
    targetSdkVersion 28
    versionCode 1
    versionName "1.0"
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}
}

dependencies {

def nav_version = "1.0.0-alpha01"

implementation fileTree(dir: 'libs', include: ['*.jar'])

implementation 'androidx.constraintlayout:constraintlayout:1.1.0' // Constraint layout

implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version" // Kotlin

// Anko
implementation "org.jetbrains.anko:anko-commons:$anko_version" // Anko Commons
implementation "org.jetbrains.anko:anko-design:$anko_version" // For SnackBars
implementation "org.jetbrains.anko:anko-coroutines:$anko_version" // Anko Coroutines

// Support libraries
implementation 'androidx.legacy:legacy-support-v4:1.0.0-alpha1' // Support v4
implementation 'androidx.appcompat:appcompat:1.0.0-alpha1' // AppCompat
implementation 'androidx.recyclerview:recyclerview:1.0.0-alpha1' // RecyclerView
implementation 'com.google.android.material:material:1.0.0-alpha1' // Design Support library
implementation 'androidx.cardview:cardview:1.0.0-alpha1' // CardView

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

// Dagger 2
implementation 'com.google.dagger:dagger:2.14.1'
kapt 'com.google.dagger:dagger-compiler:2.14.1'
provided 'javax.annotation:jsr250-api:1.0'

// Retrofit, OkHttp, OkHttpInterceptor and GSON
implementation 'com.squareup.retrofit2:retrofit:2.3.0'
implementation 'com.squareup.retrofit2:converter-gson:2.3.0'
implementation 'com.google.code.gson:gson:2.8.2'
implementation 'com.squareup.okhttp3:logging-interceptor:3.10.0'

implementation 'com.rengwuxian.materialedittext:library:2.1.4' // Material EditText
 }

kotlin {
experimental {
    coroutines "enable"
}
}

托管NavHostFragment的活动代码

override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_home_page)

// Handle the clicks for bottom navigation view
bottom_navigation_view_homepage_activity.setOnNavigationItemSelectedListener { item ->


    when (item.itemId) {
        R.id.action_appointment -> findNavController(item.itemId).navigate(R.id.appointmentFragment)

        R.id.action_chat -> findNavController(item.itemId).navigate(R.id.chatFragment)
    }



}

Navigation.findNavController(this, R.id.appointmentFragment)

}

活动的XML文件

 <?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">

    <fragment
        android:id="@+id/nav_host_fragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:name="androidx.navigation.fragment.NavHostFragment"
        app:navGraph="@navigation/nav_graph"
        app:defaultNavHost="true"
       />
    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottom_navigation_view_homepage_activity"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorPrimary"
        app:itemIconTint="@drawable/nav_item_color_state"
        app:itemTextColor="@drawable/nav_item_color_state"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:menu="@menu/bottom_navigation_view" />
</androidx.constraintlayout.widget.ConstraintLayout>

我已正确实施导航图。此外，该项目被重构为AndroidX。

Answer 1

如果在使用发布版本时发生此问题，则很可能是Proguard缩小了类名。这样，XML文件中的引用android:name="androidx.navigation.fragment.NavHostFragment"将不匹配任何有效的类。

尝试在proguard文件中添加此行

-keepnames class androidx.navigation.fragment.NavHostFragment

这样就不会使类名变小，并且保持XML文件中提到的那样。

Answer 2

尝试致电Navigation.findNavController(bottom_navigation_view_homepage_activity, R.id.appointmentFragment)

您也不需要设置setOnNavigationItemSelectedListener，只需按照以下步骤编辑导航图“ nav_graph”：

<fragment
        android:id="@+id/action_appointment"
        ..../>
<fragment
        android:id="@+id/action_chat"
        ..../>

基本上，您在nav_graph中设置的片段ID与底部导航视图中的项目ID相同。

Answer 3

在Kotlin中，您不需要调用findviewbyid，请在您的布局中实现数据绑定。
请检查在Bootomnavigaiton中调用的“ id_menu”是否与导航图中的“ id_fragment”相同

您可以使用此方法对bottom_nav进行导航，以显示类似于他的片段

setSupportActionBar（工具栏）

navController = Navigation.findNavController(this, R.id.main_fragment)
NavigationUI.setupWithNavController(bottom_nav,navController)
NavigationUI.setupActionBarWithNavController(this, navController)

也不要忘记覆盖此方法

override fun onSupportNavigateUp(): Boolean {
    return NavigationUI.navigateUp(navController,null)
}

请告诉我这段代码是否有效。

Answer 4

您是否添加了片段依赖项？实现“androidx.fragment:fragment:1.2.0”这是针对java的我不知道kotlin是否一样

找到NavHostFragment Jetpack导航Android时出错

4 个答案: