如何使用 Kotlin、Coroutines、ViewModel、LiveData 處理查詢方法的返回類型房間

Question

如何使用 Kotlin、Coroutines、ViewModel、LiveData 處理查詢方法的返回類型房間

建築物失敗了，我收到很多指向我的 Dao 類的錯誤，錯誤是

錯誤一：

不確定如何處理查詢方法的返回類型（java.lang.Object）。 DELETE 查詢方法必須返回 void 或 int（刪除的行數）。

錯誤2：

錯誤：查詢方法參數應該是可以轉換為數據庫列的類型或包含此類類型的列表/數組。 您可以考慮為此添加一個類型適配器。 kotlin.coroutines.Continuation<? super kotlin.Unit> 延續）；

錯誤 3：

錯誤：未使用的參數：延續 public abstract java.lang.Object clear(@org.jetbrains.annotations.NotNull()

錯誤 4：

錯誤：參數的類型必須是使用@Entity 注釋的類或其集合/數組。 kotlin.coroutines.Continuation<? super kotlin.Unit> 延續）；

錯誤 5：

錯誤：不確定如何處理插入方法的返回類型。 公共抽象 java.lang.Object 插入（@org.jetbrains.annotations.NotNull()

**這是我的完整代碼： https ://drive.google.com/drive/folders/1qWoud5XogzkTmpa-GWxLJStfdUPSoV7r?usp=sharing

android kotlin - Coroutines Room ViewModel LiveData MainActivity.kt

package com.example.coroutine

import android.os.Bundle
import android.text.method.ScrollingMovementMethod
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import kotlinx.android.synthetic.main.activity_main.*
import java.util.UUID
import kotlin.random.Random


class MainActivity : AppCompatActivity() {

    private lateinit var model: StudentViewModel

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

        // make text view text scrollable
        textView.movementMethod = ScrollingMovementMethod()

        // initialize the student view model
        model = ViewModelProvider(this).get(StudentViewModel::class.java)


        // observe the students live data
        model.students.observe(this, Observer { students->
                textView.text = "Students(${students.size})..."

                students.forEach {
                    textView.append("\n${it.id} | ${it.fullName} : ${it.result}")
                }
            }
        )


        btnInsert.setOnClickListener {
            // generate a new student
            val student = Student(
                null,
                UUID.randomUUID().toString(),
                Random.nextInt(100)
            )

            // insert new student into room database
            model.insert(student)
        }


        btnClear.setOnClickListener {
            // delete all students from room student table
            model.clear()
        }
    }
}

activity_main.xml

<?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"
    android:background="#FAE6FA"
    tools:context=".MainActivity">

    <com.google.android.material.button.MaterialButton
        android:id="@+id/btnInsert"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:backgroundTint="#8DB600"
        android:text="Insert"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <com.google.android.material.button.MaterialButton
        android:id="@+id/btnClear"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:backgroundTint="#E52B50"
        android:text="Clear"
        app:layout_constraintBottom_toBottomOf="@+id/btnInsert"
        app:layout_constraintStart_toEndOf="@+id/btnInsert" />

    <com.google.android.material.textview.MaterialTextView
        android:id="@+id/textView"
        style="@style/TextAppearance.MaterialComponents.Subtitle1"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:textColor="#1B1811"
        android:textStyle="bold"
        android:padding="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btnInsert"
        app:layout_constraintVertical_bias="1.0"
        tools:text="TextView" />

</androidx.constraintlayout.widget.ConstraintLayout>

RoomSingleton.kt

package com.example.coroutine

import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
import android.content.Context

@Database(entities = [Student::class], version = 1)
abstract class RoomSingleton : RoomDatabase() {
    abstract fun studentDao():StudentDao

    companion object {
        private var INSTANCE: RoomSingleton? = null
        fun getInstance(context: Context): RoomSingleton {
            if (INSTANCE == null) {
                INSTANCE = Room.databaseBuilder(
                    context,
                    RoomSingleton::class.java,
                    "roomdb")
                    .build()
            }
            return INSTANCE as RoomSingleton
        }
    }
}

RoomDao.kt

package com.example.coroutine

import androidx.lifecycle.LiveData
import androidx.room.Dao
import androidx.room.Insert
import androidx.room.OnConflictStrategy
import androidx.room.Query

@Dao
interface StudentDao{
    @Query("SELECT * FROM studentTbl ORDER BY id DESC")
    fun getStudents():LiveData<List<Student>>

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insert(student:Student)

    @Query("DELETE FROM studentTbl")
    suspend fun clear()
}

RoomEntity.kt

package com.example.coroutine

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

@Entity(tableName = "studentTbl")
data class Student(
    @PrimaryKey
    var id:Long?,

    @ColumnInfo(name = "uuid")
    var fullName: String,

    @ColumnInfo(name = "result")
    var result:Int
)

學生視圖模型.kt

package com.example.coroutine

import androidx.lifecycle.AndroidViewModel
import android.app.Application
import androidx.lifecycle.LiveData
import androidx.lifecycle.viewModelScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch


class StudentViewModel(application:Application): AndroidViewModel(application){
    private val db:RoomSingleton = RoomSingleton.getInstance(application)

    internal val students : LiveData<List<Student>> = db.studentDao().getStudents()

    fun insert(student: Student){
        viewModelScope.launch(Dispatchers.IO) {
            db.studentDao().insert(student)
        }
    }

    fun clear(){
        viewModelScope.launch(Dispatchers.IO) {
            db.studentDao().clear()
        }
    }
}

Answer 1

您在方法插入和刪除中的關鍵字 suspend 中的問題。 刪除后你的錯誤就消失了。

@Insert(onConflict = OnConflictStrategy.REPLACE)
   fun insert(student:Student)

    @Query("DELETE FROM studentTbl")
   fun clear()

順便說一句，您的構建仍然無法成功。 要修復其他錯誤，您應該在應用 build.gradle 文件中的塊插件上添加“kotlin-android-extensions”。

plugins {
    id 'com.android.application'
    id 'kotlin-android-extensions'
    id 'kotlin-android'
    id 'kotlin-kapt'
}

但是此解決方案已棄用，您應該改用 viewBinding。 看一下這個。 https://developer.android.com/topic/libraries/view-binding/migration

Answer 2

復制您的代碼，禁止 gradle 文件，並對主要活動進行輕微調整。 編譯正常並運行插入和清除按鈕似乎工作正常。

因此，要么您構建的 gradle 不正確，要么您需要對項目進行清理或重建。

例如：-

我使用的 MainActivity 將視圖聲明為 lateinit 的，而 findViewById 的則晚了：-

class MainActivity : AppCompatActivity() {

    private lateinit var model: StudentViewModel
    lateinit var textView: TextView
    lateinit var btnClear: Button
    lateinit var btnInsert: Button

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        textView = this.findViewById(R.id.textView)
        btnClear = this.findViewById(R.id.btnClear)
        btnInsert = this.findViewById(R.id.btnInsert)

        // make text view text scrollable
        textView.movementMethod = ScrollingMovementMethod()

        // initialize the student view model
        model = ViewModelProvider(this).get(StudentViewModel::class.java)


        // observe the students live data
        model.students.observe(this, Observer { students->
            textView.text = "Students(${students.size})..."

            students.forEach {
                textView.append("\n${it.id} | ${it.fullName} : ${it.result}")
            }
        }
        )


        btnInsert.setOnClickListener {
            // generate a new student
            val student = Student(
                    null,
                    UUID.randomUUID().toString(),
                    Random.nextInt(100)
            )

            // insert new student into room database
            model.insert(student)
        }


        btnClear.setOnClickListener {
            // delete all students from room student table
            model.clear()
        }
    }
}

使用的構建 Gradle（模塊）：-

plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-kapt'
}

android {
    compileSdk 31

    defaultConfig {
        applicationId "a.a.so69998391kotlinroom_to_handle_query_return_types"
        minSdk 21
        targetSdk 31
        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'
    }
}

dependencies {

    implementation 'androidx.core:core-ktx:1.7.0'
    implementation 'androidx.appcompat:appcompat:1.3.1'
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.1'
    implementation 'androidx.room:room-ktx:2.4.0-beta01'
    implementation 'androidx.room:room-runtime:2.4.0-beta01'
    implementation 'androidx.lifecycle:lifecycle-common:2.4.0'
    implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.4.0'
    implementation 'androidx.lifecycle:lifecycle-viewmodel-savedstate:2.4.0'
    implementation 'androidx.lifecycle:lifecycle-viewmodel-compose:2.4.0'
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
    kapt 'androidx.lifecycle:lifecycle-compiler:2.4.0'
    kapt 'androidx.room:room-compiler:2.4.0-beta01'
}

Answer 3

在 Dao 函數中使用協程時我遇到了同樣的問題

對我來說只是改變

kapt "androidx.room:room-compiler:$room_version"

至

annotationProcessor "androidx.room:room-compiler:$room_version"

如果您使用List or MutableLiveData檢查此答案