Question

在有人说这之前已经被回答之前，我已经阅读并尝试了下面列出的帖子中的推荐解决方案：

我尝试在build.gradle文件中添加依赖项，尝试使用ViewModel类的不同实现，但没有任何改变。

我得到的主要错误是

Process: com.example.infinityquiz, PID: 12107
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.infinityquiz/com.example.infinityquiz.MainActivity}: java.lang.RuntimeException: Cannot create an instance of class com.example.infinityquiz.viewmodel.QuestionViewModel

在下面，我列出了我当前的相关代码。如果您认为缺少重要的代码，请告诉我。

Build.gradle


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


android {
    compileSdkVersion 29
    buildToolsVersion "30.0.0"

    defaultConfig {
        applicationId "com.example.infinityquiz"
        minSdkVersion 23
        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'
        }
    }

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

    kotlinOptions {
        jvmTarget = JavaVersion.VERSION_1_8.toString()
    }
}

dependencies {
    implementation fileTree(dir: "libs", include: ["*.jar"])
    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    implementation 'androidx.core:core-ktx:1.3.1'
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.1'
    testImplementation 'junit:junit:4.13'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'

    // Navigation Component
    implementation 'androidx.navigation:navigation-fragment-ktx:2.3.0'
    implementation 'androidx.navigation:navigation-ui-ktx:2.3.0'

    // Room components
    implementation "androidx.room:room-runtime:2.2.5"
    kapt "androidx.room:room-compiler:2.2.5"
    implementation "androidx.room:room-ktx:2.2.5"
    androidTestImplementation "androidx.room:room-testing:2.2.5"
    implementation "androidx.paging:paging-runtime:2.1.2"

    // Lifecycle components
    implementation "androidx.lifecycle:lifecycle-extensions:2.2.0"
    implementation "androidx.lifecycle:lifecycle-common-java8:2.2.0"
    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0"

    // Kotlin components
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.3.72"
    api "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.7"
    api "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.3.5"

    // Extensions = ViewModel + LiveData
    implementation "android.arch.lifecycle:extensions:1.1.1"
    kapt "android.arch.lifecycle:compiler:1.1.1"
    // Room
    implementation "android.arch.persistence.room:runtime:1.1.1"
    kapt "android.arch.persistence.room:compiler:1.1.1"

    implementation 'androidx.fragment:fragment:1.2.5'
}

ViewModel

package com.example.infinityquiz.viewmodel

import android.app.Application
import androidx.lifecycle.AndroidViewModel
import com.example.infinityquiz.data.QuestionDatabase
import com.example.infinityquiz.model.Question
import com.example.infinityquiz.repository.QuestionRepository

class QuestionViewModel(application: Application): AndroidViewModel(application) {
    val question: Question
    private val repository:QuestionRepository

    init {
        val questionDao = QuestionDatabase.getDatabase(
            application
        ).questionDao()
        repository = QuestionRepository(questionDao)
        question = repository.question
    }
}

存储库

package com.example.infinityquiz.repository

import com.example.infinityquiz.data.QuestionDao
import com.example.infinityquiz.model.Question

class QuestionRepository(private val questionDao: QuestionDao) {
    val question: Question = questionDao.readRandomQuestion()
}

Dao

package com.example.infinityquiz.data

import androidx.room.Dao
import androidx.room.Query
import com.example.infinityquiz.model.Question

/*
private const val TABLE_NAME = "multiple_choice_questions"
private const val QUERY = "SELECT * FROM $TABLE_NAME ORDER BY RANDOM() LIMIT 1"
*/

@Dao
interface QuestionDao {
    @Query("SELECT * FROM multiple_choice_questions ORDER BY RANDOM() LIMIT 1")
    fun readRandomQuestion(): Question
}

问题

package com.example.infinityquiz.model

import android.os.Parcelable
import androidx.room.Entity
import androidx.room.PrimaryKey
import kotlinx.android.parcel.Parcelize

@Parcelize
@Entity(tableName = "multiple_choice_questions")//, foreignKeys=[], indices=[])
data class Question (
    @PrimaryKey(autoGenerate = true)
    val id: Int,
    val Question: String,
    val Category: String,
    val Subcategory: String,
    val AnswerOne: String,
    val AnswerTwo: String,
    val AnswerThree: String,
    val AnswerFour: String,
    val CorrectAnswer: Int,
    val wasQuestionSeen: Int,
    val Wikipedia: String
): Parcelable

主要活动（部分）

package com.example.infinityquiz

import android.graphics.Color
import android.graphics.Typeface
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import androidx.core.content.ContextCompat
import androidx.lifecycle.ViewModelProvider
import com.example.infinityquiz.model.Question
import com.example.infinityquiz.viewmodel.QuestionViewModel
import kotlinx.android.synthetic.main.activity_quiz_questions.*

class MainActivity : AppCompatActivity(), View.OnClickListener{
    private lateinit var mQuestionViewModel: QuestionViewModel
    private var question: Question? = null
    private var mSelectedOptionPosition: Int = 0

    /**
     * This function is auto created by Android when the Activity Class is created.
     */
    override fun onCreate(savedInstanceState: Bundle?) {
        //This call the parent constructor
        super.onCreate(savedInstanceState)
        // This is used to align the xml view to this class
        setContentView(R.layout.activity_main)


        mQuestionViewModel = ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory.getInstance(this.application)).get(QuestionViewModel::class.java)
        // mQuestionViewModel = ViewModelProvider(this).get(QuestionViewModel::class.java)

        setQuestion()

        tv_option_one.setOnClickListener(this)
        tv_option_two.setOnClickListener(this)
        tv_option_three.setOnClickListener(this)
        tv_option_four.setOnClickListener(this)
        btn_submit.setOnClickListener(this)
    }
.
.
.
}

数据库

package com.example.infinityquiz.data

import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
import com.example.infinityquiz.model.Question

@Database(entities = [Question::class], version = 1)
abstract class QuestionDatabase: RoomDatabase() {
    abstract fun questionDao(): QuestionDao

    companion object {
        @Volatile
        private var INSTANCE: QuestionDatabase? = null
        private const val PATH = "database/data_eng.db"
        private const val NAME = "multiple_choice_questions"

        private fun buildDatabase(context: Context) =
            Room.databaseBuilder(context.applicationContext, QuestionDatabase::class.java, NAME).createFromAsset(PATH).build()


        fun getDatabase(context: Context): QuestionDatabase{
            val tempInstance = INSTANCE
            if(tempInstance != null){
                return tempInstance
            }
            synchronized(this){
                val instance = buildDatabase(context)
                INSTANCE = instance
                return instance
            }
        }
    }
}

错误消息

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.infinityquiz, PID: 12107
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.infinityquiz/com.example.infinityquiz.MainActivity}: java.lang.RuntimeException: Cannot create an instance of class com.example.infinityquiz.viewmodel.QuestionViewModel
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.RuntimeException: Cannot create an instance of class com.example.infinityquiz.viewmodel.QuestionViewModel
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:275)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
        at com.example.infinityquiz.MainActivity.onCreate(MainActivity.kt:32)
        at android.app.Activity.performCreate(Activity.java:7802)
        at android.app.Activity.performCreate(Activity.java:7791)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Constructor.newInstance0(Native Method)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
        at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:267)
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187) 
        at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150) 
        at com.example.infinityquiz.MainActivity.onCreate(MainActivity.kt:32) 
        at android.app.Activity.performCreate(Activity.java:7802) 
        at android.app.Activity.performCreate(Activity.java:7791) 
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299) 
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245) 
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
     Caused by: java.lang.IllegalStateException: Pre-packaged database has an invalid schema: multiple_choice_questions(com.example.infinityquiz.model.Question).
     Expected:
    TableInfo{name='multiple_choice_questions', columns={Category=Column{name='Category', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, Subcategory=Column{name='Subcategory', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, wasQuestionSeen=Column{name='wasQuestionSeen', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}, AnswerThree=Column{name='AnswerThree', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, Wikipedia=Column{name='Wikipedia', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, Question=Column{name='Question', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, id=Column{name='id', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=1, defaultValue='null'}, AnswerOne=Column{name='AnswerOne', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, CorrectAnswer=Column{name='CorrectAnswer', type='INTEGER', affinity='3', notNull=true, primaryKeyPosition=0, defaultValue='null'}, AnswerTwo=Column{name='AnswerTwo', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}, AnswerFour=Column{name='AnswerFour', type='TEXT', affinity='2', notNull=true, primaryKeyPosition=0, defaultValue='null'}}, foreignKeys=[], indices=[]}
     Found:
    TableInfo{name='multiple_choice_questions', columns={}, foreignKeys=[], indices=[]}
        at androidx.room.RoomOpenHelper.checkIdentity(RoomOpenHelper.java:163)
E/AndroidRuntime:     at androidx.room.RoomOpenHelper.onOpen(RoomOpenHelper.java:135)
        at androidx.sqlite.db.framework.FrameworkSQLiteOpenHelper$OpenHelper.onOpen(FrameworkSQLiteOpenHelper.java:142)
        at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:428)
        at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:317)
        at androidx.sqlite.db.framework.FrameworkSQLiteOpenHelper$OpenHelper.getWritableSupportDatabase(FrameworkSQLiteOpenHelper.java:92)
        at androidx.sqlite.db.framework.FrameworkSQLiteOpenHelper.getWritableDatabase(FrameworkSQLiteOpenHelper.java:53)
        at androidx.room.SQLiteCopyOpenHelper.getWritableDatabase(SQLiteCopyOpenHelper.java:90)
        at androidx.room.RoomDatabase.inTransaction(RoomDatabase.java:476)
        at androidx.room.RoomDatabase.assertNotSuspendingTransaction(RoomDatabase.java:281)
        at com.example.infinityquiz.data.QuestionDao_Impl.readRandomQuestion(QuestionDao_Impl.java:25)
        at com.example.infinityquiz.repository.QuestionRepository.<init>(QuestionRepository.kt:7)
        at com.example.infinityquiz.viewmodel.QuestionViewModel.<init>(QuestionViewModel.kt:17)
            ... 21 more
Disconnected from the target VM, address: 'localhost:8608', transport: 'socket'

我无法立即解决此问题。谢谢您的提前帮助。

无法在Kotlin中创建com.example ... ViewModel类的实例

0 个答案: