Android Hilt问题：ViewModel依赖注入报错，提示无无参构造方法

问题描述 #

严格按照Hilt ViewModel文档实现Android基础依赖注入，但应用启动直接崩溃，报错提示找不到ViewModel的无参构造方法，尽管已经通过构造方法注入了HealthConnectClient依赖。

错误栈追踪 #

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myHealthConnect.myweightaverage/com.myHealthConnect.myweightaverage.activity.MainActivity}: java.lang.RuntimeException: Cannot create an instance of class com.myHealthConnect.myweightaverage.viewmodel.MainActivityViewModel
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4169)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4325)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:101)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2574)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loopOnce(Looper.java:226)
    at android.os.Looper.loop(Looper.java:313)
    at android.app.ActivityThread.main(ActivityThread.java:8757)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:571)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1067)
Caused by: java.lang.RuntimeException: Cannot create an instance of class com.myHealthConnect.myweightaverage.viewmodel.MainActivityViewModel
    at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.kt:204)
    at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:324)
    at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:306)
    at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.kt:280)
    at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.kt:128)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:187)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.kt:153)
    at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:53)
    at androidx.lifecycle.ViewModelLazy.getValue(ViewModelLazy.kt:35)
    at com.myHealthConnect.myweightaverage.activity.MainActivity.getViewModel(MainActivity.kt:21)
    at com.myHealthConnect.myweightaverage.activity.MainActivity.onCreate(MainActivity.kt:29)
    at android.app.Activity.performCreate(Activity.java:8591)
    at android.app.Activity.performCreate(Activity.java:8570)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1384)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:4150)
    ... 12 more
Caused by: java.lang.NoSuchMethodException: com.myHealthConnect.myweightaverage.viewmodel.MainActivityViewModel.<init> []
    at java.lang.Class.getConstructor0(Class.java:2363)
    at java.lang.Class.getDeclaredConstructor(Class.java:2201)
    at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.kt:202)
    ... 26 more

相关代码文件 #

项目级build.gradle #

// Top-level build file where you can add configuration options common to all sub-projects/modules.
plugins {
    id 'com.android.application' version '7.3.0' apply false
    id 'com.android.library' version '7.3.0' apply false
    id 'org.jetbrains.kotlin.android' version '1.8.0' apply false
    id 'com.google.dagger.hilt.android' version '2.45' apply false
}

应用级build.gradle #

plugins {
    id 'com.android.application'
    id 'org.jetbrains.kotlin.android'
    id 'kotlin-kapt'
    id("com.google.dagger.hilt.android") version "2.45" apply false
}

android {
    namespace 'com.myHealthConnect.myweightaverage'
    compileSdk 33

    defaultConfig {
        applicationId "com.myHealthConnect.myweightaverage"
        minSdk 26
        targetSdk 33
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
    dataBinding {
        enabled = true
    }
}

dependencies {

    implementation 'androidx.core:core-ktx:1.10.0'
    implementation 'androidx.appcompat:appcompat:1.6.1'
    implementation 'com.google.android.material:material:1.8.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
    implementation 'androidx.health.connect:connect-client:1.0.0-alpha11'
    implementation "androidx.activity:activity-ktx:1.7.0"
    testImplementation 'junit:junit:4.13.2'
    implementation("com.google.dagger:hilt-android:2.45")
    kapt("com.google.dagger:hilt-android-compiler:2.45")
    androidTestImplementation 'androidx.test.ext:junit:1.1.5'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
}

// Allow references to generated code
kapt {
    correctErrorTypes = true

    javacOptions {
        option("-Adagger.hilt.android.internal.disableAndroidSuperclassValidation=true")
    }
}

AndroidManifest.xml #

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
          xmlns:tools="http://schemas.android.com/tools">

    <!-- Check whether Health Connect is installed or not -->
    <queries>
        <package android:name="com.google.android.apps.healthdata" />
    </queries>

    <uses-permission android:name="android.permission.health.READ_WEIGHT"/>

    <application
            android:name=".application.MyApplication"
            android:allowBackup="true"
            android:dataExtractionRules="@xml/data_extraction_rules"
            android:fullBackupContent="@xml/backup_rules"
            android:icon="@mipmap/ic_launcher"
            android:label="@string/app_name"
            android:roundIcon="@mipmap/ic_launcher_round"
            android:supportsRtl="true"
            android:theme="@style/Theme.MyWeightAverage"
            android:appComponentFactory="androidx.core.app.CoreComponentFactory"
            tools:replace="android:appComponentFactory"
            tools:targetApi="31">

        <activity
                android:name=".activity.MainActivity"
                android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>

                <category android:name="android.intent.category.LAUNCHER"/>

                <action android:name="androidx.health.ACTION_SHOW_PERMISSIONS_RATIONALE" />
            </intent-filter>

            <meta-data
                    android:name="android.app.lib_name"
                    android:value=""/>
        </activity>
    </application>

</manifest>

MyApplication.kt #

import android.app.Application
import dagger.hilt.android.HiltAndroidApp

@HiltAndroidApp
class MyApplication : Application()

AppModule.kt #

import android.content.Context
import androidx.health.connect.client.HealthConnectClient
import dagger.Module
import dagger.Provides
import dagger.hilt.InstallIn
import dagger.hilt.android.components.ViewModelComponent
import dagger.hilt.android.qualifiers.ApplicationContext
import dagger.hilt.android.scopes.ViewModelScoped
import dagger.hilt.components.SingletonComponent
import javax.inject.Singleton

@Module
@InstallIn(ViewModelComponent::class)
object AppModule {

    @Provides
    @ViewModelScoped
    fun provideHealthConnectClient(@ApplicationContext appContext: Context) =
        if (HealthConnectClient.isProviderAvailable(appContext)) {
            HealthConnectClient.getOrCreate(appContext)
        } else {
            throw NullPointerException()
        }
}

MainActivity.kt #

import android.os.Bundle
import androidx.activity.viewModels
import androidx.appcompat.app.AppCompatActivity
import androidx.databinding.DataBindingUtil
import com.myHealthConnect.myweightaverage.R
import com.myHealthConnect.myweightaverage.databinding.ActivityMainBinding
import com.myHealthConnect.myweightaverage.viewmodel.MainActivityViewModel
import dagger.hilt.android.AndroidEntryPoint

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {

    private val viewModel: MainActivityViewModel by viewModels()

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

        val binding: ActivityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main)
        binding.viewModel = viewModel
        binding.lifecycleOwner = this
    }
}

MainActivityViewModel.kt #

import androidx.health.connect.client.HealthConnectClient
import androidx.lifecycle.ViewModel
import dagger.hilt.android.lifecycle.HiltViewModel
import javax.inject.Inject

@HiltViewModel
class MainActivityViewModel @Inject constructor(
    val healthConnectClient: HealthConnectClient
) : ViewModel() {
    init {
    }
}

解决方案 #

1. 修复Hilt插件配置（核心问题） #

错误根源是应用级build.gradle中Hilt插件被设置为apply false，导致Hilt无法生成ViewModel注入所需的代码，系统只能尝试用默认的NewInstanceFactory创建ViewModel，而你的ViewModel没有无参构造方法，因此崩溃。

修改应用级build.gradle的plugins块：

plugins {
    id 'com.android.application'
    id 'org.jetbrains.kotlin.android'
    id 'kotlin-kapt'
    // 移除apply false，让插件在当前模块生效
    id("com.google.dagger.hilt.android") version "2.45"
}

2. 修复MainActivity的布局重复设置问题 #

MainActivity中调用了两次setContentView，会导致布局重复初始化，保留DataBinding的初始化代码即可：

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    // 移除重复的setContentView调用
    // setContentView(R.layout.activity_main)

    val binding: ActivityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main)
    binding.viewModel = viewModel
    binding.lifecycleOwner = this
}

3. 可选：优化AppModule的异常处理 #

当前provideHealthConnectClient在Health Connect不可用时抛出NullPointerException，建议换成更明确的自定义异常或者返回null（配合@Nullable注解），方便上层处理：

@Provides
@ViewModelScoped
fun provideHealthConnectClient(@ApplicationContext appContext: Context): HealthConnectClient? =
    if (HealthConnectClient.isProviderAvailable(appContext)) {
        HealthConnectClient.getOrCreate(appContext)
    } else {
        null
    }

修改完成后，执行Clean Project -> Rebuild Project，再运行应用即可解决崩溃问题。

内容的提问来源于stack exchange，提问作者Harry Angus