Kotlin: java .lang.RuntimeException: невозможно создать экземпляр класса ViewModel - PullRequest
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Kotlin: java .lang.RuntimeException: невозможно создать экземпляр класса ViewModel

0 голосов
/ 26 марта 2020

Это мой первый проект, использующий Kotlin, поэтому я практикую создание приложения и использование компонентов архитектуры Room Database, Android View Model и LiveData, но я получил это сообщение об ошибке. И мобильный кр sh неожиданно,

Я не знаю, как это решить.

Спасибо.

build.gradle 

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

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.2"

    defaultConfig {
        applicationId "com.leaf76.architectureexample"
        minSdkVersion 21
        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'
        }
    }

}

dependencies {
    def lifecycle_version = "2.2.0"
    def room_version = "2.2.5"


    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'androidx.appcompat:appcompat:1.1.0'
    // com.android.support.cardview => androidx
    implementation "androidx.cardview:cardview:1.0.0"
    // com.android.support.design => androidx
    implementation "com.google.android.material:material:1.0.0"

    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'

    // ViewModel
    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
    // LiveData
    implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"
    // Annotation processor
    kapt "androidx.lifecycle:lifecycle-compiler:$lifecycle_version"

    // Room
    implementation "androidx.room:room-runtime:$room_version"
    kapt "androidx.room:room-compiler:$room_version"
    implementation "androidx.room:room-ktx:$room_version"

}

Сообщение об ошибке 

2020-03-27 02:50:27.987 12708-12708/com.leaf76.architectureexample E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.leaf76.architectureexample, PID: 12708
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.leaf76.architectureexample/com.leaf76.architectureexample.MainActivity}: java.lang.RuntimeException: Cannot create an instance of class com.leaf76.architectureexample.NoteViewModel
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3448)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3595)
    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$H.handleMessage(ActivityThread.java:2147)
    at android.os.Handler.dispatchMessage(Handler.java:107)
    at android.os.Looper.loop(Looper.java:237)
    at android.app.ActivityThread.main(ActivityThread.java:7811)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1076)
 Caused by: java.lang.RuntimeException: Cannot create an instance of class com.leaf76.architectureexample.NoteViewModel
    at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:221)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
    at com.leaf76.architectureexample.MainActivity.onCreate(MainActivity.kt:21)
    at android.app.Activity.performCreate(Activity.java:7955)
    at android.app.Activity.performCreate(Activity.java:7944)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1307)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3423)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3595) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2147) 
    at android.os.Handler.dispatchMessage(Handler.java:107) 
    at android.os.Looper.loop(Looper.java:237) 
    at android.app.ActivityThread.main(ActivityThread.java:7811) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1076) 
 Caused by: java.lang.InstantiationException: java.lang.Class<com.leaf76.architectureexample.NoteViewModel> has no zero argument constructor
    at java.lang.Class.newInstance(Native Method)
    at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:219)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187) 
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150) 
    at com.leaf76.architectureexample.MainActivity.onCreate(MainActivity.kt:21) 
    at android.app.Activity.performCreate(Activity.java:7955) 
    at android.app.Activity.performCreate(Activity.java:7944) 
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1307) 
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3423) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3595) 
    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$H.handleMessage(ActivityThread.java:2147) 
    at android.os.Handler.dispatchMessage(Handler.java:107) 
    at android.os.Looper.loop(Looper.java:237) 
    at android.app.ActivityThread.main(ActivityThread.java:7811) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1076)

Note.kt 

package com.leaf76.architectureexample

import androidx.room.Entity
import androidx.room.PrimaryKey

@Entity(tableName = "note_table")
data class Note(var title: String, var description: String, var priorty: Int) {

    @PrimaryKey(autoGenerate = true)
    var Id: Int = 0
}

NoteDatabase 

package com.leaf76.architectureexample

import android.content.Context
import android.os.AsyncTask
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
import androidx.sqlite.db.SupportSQLiteDatabase

@Database(entities = [Note::class], version = 1, exportSchema = false)
abstract class NoteDatabase : RoomDatabase() {

    abstract fun noteDao(): NoteDao

    // static parameters
    companion object {

        private lateinit var instance: NoteDatabase

        fun getInstance(context: Context): NoteDatabase {
            if (instance == null) {
                synchronized(NoteDatabase::class.java) {
                    instance = Room.databaseBuilder(
                        context.applicationContext,
                        NoteDatabase::class.java, "note_database"
                    )
                        .fallbackToDestructiveMigration()
                        .addCallback(roomCallbackL)
                        .build()
                }
            }
            return instance
        }

        private val roomCallbackL: Callback = object : Callback() {
            override fun onCreate(db: SupportSQLiteDatabase) {
                super.onCreate(db)
                PopulateDbAsyncTask(instance).execute()
            }
        }

        private class PopulateDbAsyncTask(db: NoteDatabase) : AsyncTask<Void, Void, Void>() {

            private val noteDao: NoteDao = db.noteDao()

            override fun doInBackground(vararg voids: Void): Void? {
                noteDao.insert(Note("Title1", "Description1", 1))
                noteDao.insert(Note("Title2", "Description2", 2))
                noteDao.insert(Note("Title3", "Description3", 3))
                return null
            }
        }

    }

}

NoteRepository package com.leaf76.architectureexample 

import android.app.Application
import android.os.AsyncTask
import androidx.lifecycle.LiveData

class NoteRepository(application: Application) {
    // The lateinit avoid Nullable
    private var noteDao: NoteDao

    private var allNotes: LiveData<List<Note>>

    init {
        val database = NoteDatabase.getInstance(application.applicationContext)
        noteDao = database.noteDao()
        allNotes = noteDao.getAllNotes()
    }

    fun insert(note: Note) {
        InsertNoteAsyncTask(noteDao).execute(note)
    }

    fun update(note: Note) {
        UpdateNoteAsyncTask(noteDao).execute(note)
    }

    fun delete(note: Note) {
        DeleteNoteAsyncTask(noteDao).execute(note)
    }

    fun deleteAllnotes() {
        DeleteAllNotesAsyncTask(noteDao).execute()
    }

    fun getAllNotes(): LiveData<List<Note>> {
        return allNotes
    }

    companion object {
        // Insert note
        private class InsertNoteAsyncTask(var noteDao: NoteDao) :
            AsyncTask<Note, Void, Void>() {

            override fun doInBackground(vararg notes: Note): Void? {
                noteDao.insert(notes[0])
                return null
            }
        }

        // Update note
        private class UpdateNoteAsyncTask(var noteDao: NoteDao) :
            AsyncTask<Note, Void, Void>() {

            override fun doInBackground(vararg notes: Note): Void? {
                noteDao.update(notes[0])
                return null
            }
        }

        // Delete note
        private class DeleteNoteAsyncTask(var noteDao: NoteDao) :
            AsyncTask<Note, Void, Void>() {

            override fun doInBackground(vararg notes: Note): Void? {
                noteDao.delete(notes[0])
                return null
            }
        }

        // Delete all note
        private class DeleteAllNotesAsyncTask(var noteDao: NoteDao) :
            AsyncTask<Void, Void, Void>() {

            override fun doInBackground(vararg voids: Void): Void? {
                noteDao.deleteAllNotes()
                return null
            }
        }
    }

}

NoteViewModel 

package com.leaf76.architectureexample

import android.app.Application
import androidx.lifecycle.AndroidViewModel
import androidx.lifecycle.LiveData

class NoteViewModel(application: Application) : AndroidViewModel(application) {

    private var repository: NoteRepository = NoteRepository(application)
    private var allNotes: LiveData<List<Note>> = repository.getAllNotes()

    fun insert(note: Note){
        repository.insert(note)
    }

    fun update(note:Note){
        repository.update(note)
    }

    fun delete(note: Note){
        repository.delete(note)
    }

    fun deleteAllNotes(){
        repository.deleteAllnotes()
    }

    fun getAllNotes(): LiveData<List<Note>>{
        return allNotes
    }

}

MainActivity 

package com.leaf76.architectureexample

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.widget.Toast
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider

class MainActivity : AppCompatActivity() {
    private val TAG: String = "MainActivity"

    private lateinit var noteViewModel: NoteViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        Log.i(TAG,"MainActivity entry on create")

        noteViewModel = ViewModelProvider(this).get(NoteViewModel::class.java)
        Log.i(TAG,"Get note view model")

        noteViewModel.getAllNotes().observe(this, Observer<List<Note>> {
            Toast.makeText(this,"onChanged",Toast.LENGTH_LONG).show()
        })
        Log.i(TAG, "Get Toast")
    }
}

1 Ответ

0 голосов
/ 27 марта 2020

Работает !!!

Когда я удаляю этот экземпляр == нулевое условие, но я все еще не знаю kotlin, как запустить его на шаблоне Singleton. 

    // static parameters
    companion object {

        private lateinit var instance: NoteDatabase

        fun getInstance(context: Context): NoteDatabase {
            if (instance == null) {
                synchronized(NoteDatabase::class.java) {
                    instance = Room.databaseBuilder(
                        context.applicationContext,
                        NoteDatabase::class.java, "note_database"
                    )
                        .fallbackToDestructiveMigration()
                        .addCallback(roomCallbackL)
                        .build()
                }
            }
            return instance
        }

до 

    // static parameters
    companion object {

        private lateinit var instance: NoteDatabase

        fun getInstance(context: Context): NoteDatabase {
                synchronized(NoteDatabase::class.java) {
                    instance = Room.databaseBuilder(
                        context.applicationContext,
                        NoteDatabase::class.java, "note_database"
                    )
                        .fallbackToDestructiveMigration()
                        .addCallback(roomCallbackL)
                        .build()
            }
            return instance
        }
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