Android：匕首Kotlin

我是匕首新手。 我想用Dagger 2在我的项目上使用Dependecy Injection系统。 当我调试我的项目注入字段显示为null 。

怎么了？

 class App : Application() { lateinit var component: AppComponent @Inject lateinit var database: AppDatabase //--> null?? @Inject lateinit var app: App //--> null?? override fun onCreate() { super.onCreate() component = DaggerAppComponent.builder() .appModule(AppModule(this)) .databaseModule(DatabaseModule()) .build().apply { inject(this@App) Timber.d("App: $app") } } } @AppScope @Component(modules = arrayOf(AppModule::class, DatabaseModule::class)) interface AppComponent { fun inject(application: Application) } @Module class AppModule(private val application: Application) { @Provides @AppScope fun provideApplication() = application @Provides @AppScope @ApplicationContext fun provideContext() = application.applicationContext!! } @Module(includes = arrayOf(AppModule::class)) class DatabaseModule { @Inject lateinit var context: Context private val database by lazy { Room.databaseBuilder(context, AppDatabase::class.java, AppDatabase.CONS.NAME) .build() } @Provides @AppScope fun provideDatabase(context: Context): AppDatabase = database } 

摇篮：

 apply plugin: 'com.android.application' apply plugin: 'kotlin-android' apply plugin: 'kotlin-kapt' apply plugin: 'kotlin-android-extensions' buildscript { repositories { jcenter() mavenCentral() } dependencies { classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version" classpath "org.jetbrains.kotlin:kotlin-android-extensions:$kotlin_version" } } android { compileSdkVersion 26 buildToolsVersion '26.0.2' defaultConfig { minSdkVersion 16 targetSdkVersion 26 applicationId "com.kibar.app" versionCode 1100 versionName '1.1.0' archivesBaseName = "app-$versionName-$versionCode" multiDexEnabled true javaCompileOptions { annotationProcessorOptions { includeCompileClasspath = true } } } buildTypes { release { debuggable false minifyEnabled true shrinkResources true proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt' } debug { debuggable true proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt' } } compileOptions { sourceCompatibility JavaVersion.VERSION_1_8 targetCompatibility JavaVersion.VERSION_1_8 } packagingOptions { exclude 'META-INF/rxjava.properties' } sourceSets { main.java.srcDirs += 'src/main/kotlin' } } kapt { generateStubs = true } dependencies { implementation fileTree(include: ['*.jar'], dir: 'libs') implementation 'com.android.support:multidex:1.0.2' implementation "com.android.support:design:$android_support_version" implementation "com.android.support:appcompat-v7:$android_support_version" implementation "com.android.support:recyclerview-v7:$android_support_version" implementation "com.android.support:cardview-v7:$android_support_version" implementation "com.google.firebase:firebase-ads:$firebase_version" implementation "com.google.firebase:firebase-crash:$firebase_version" implementation "com.google.firebase:firebase-config:$firebase_version" implementation 'com.google.code.gson:gson:2.8.2' implementation 'com.jakewharton.timber:timber:4.5.1' implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version" implementation "android.arch.persistence.room:runtime:$room_version" annotationProcessor "android.arch.persistence.room:compiler:$room_version" implementation "com.google.dagger:dagger:$dagger_version" implementation "com.google.dagger:dagger-android:$dagger_version" implementation "com.google.dagger:dagger-android-support:$dagger_version" kapt "android.arch.persistence.room:compiler:$room_version" kapt "com.google.dagger:dagger-android-processor:$dagger_version" kapt "com.google.dagger:dagger-compiler:$dagger_version" provided 'org.glassfish:javax.annotation:10.0-b28' } apply plugin: 'com.google.gms.google-services' 

顶级gradle：

 buildscript { ext{ android_support_version = "26.1.0" kotlin_version = "1.1.51" firebase_version = "11.4.2" room_version = "1.0.0-alpha9-1" dagger_version = "2.11" } repositories { jcenter() maven { url "https://maven.google.com" } maven { url "https://jitpack.io" } } dependencies { classpath 'com.android.tools.build:gradle:3.0.0-rc2' classpath 'com.google.gms:google-services:3.1.1' } } allprojects { repositories { jcenter() maven { url "https://maven.google.com" } maven { url "https://jitpack.io" } } gradle.projectsEvaluated { tasks.withType(JavaCompile) { options.compilerArgs << "-Xmaxerrs" << "1000" } } } 

Answer 1

 fun inject(application: Application) 

应该

 fun inject(application: App) 

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不要忘记在AndroidManifest.xml中指定App类作为application:name

 <application android:name=".application.App" 

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你必须确保你用kapt作用域来定义编译器

 kapt 'com.google.dagger:dagger-compiler:2.x' 

而且你也应用kotlin-kapt插件

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

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如果您使用字段注入，则需要指定注释目标（在Kotlin中）：

 @field:Inject lateinit var thing: Thing; 

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您还在提供者方法参数中缺少@ApplicationContext的限定符，因此也添加了该限定符。

 fun database(@ApplicationContext context: Context) : Database { ...