集合不包含与谓词匹配的元素

Question

e: [kapt] An exception occurred: java.util.NoSuchElementException: Collection contains no element matching the predicate.

以下是更详细的错误消息：

FAILURE: Build failed with an exception
* What went wrong:
Execution failed for task ':app:kaptDebugKotlin'.
> Compilation error. See log for more details

我将代码中的问题隔离在下面的某个地方，尽管我不知道抛出这个异常的具体原因：

package com.example.pomoplay

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

@Database(entities = [(Category::class)], version = 1)
abstract class PomoPlayDatabase: RoomDatabase() {

    abstract fun categoryDao(): CategoryDao

    companion object {
        private var INSTANCE: PomoPlayDatabase? = null
        internal fun getDatabase(context: Context): PomoPlayDatabase?
        {
            if (INSTANCE == null) {
                synchronized(PomoPlayDatabase::class.java) {
                    if (INSTANCE == null) {
                        INSTANCE =
                            Room.databaseBuilder<PomoPlayDatabase>(
                                context.applicationContext,
                                PomoPlayDatabase::class.java,
                                "pomoplay_database").build()
                    }
                }
            }
            return INSTANCE
        }
    }
}

gradle.build-项目

    buildscript {
        ext.kotlin_version = '1.3.61'
        repositories {
            google()
            jcenter()

        }
        dependencies {


            classpath 'androidx.navigation:navigation-safe-args-gradle-plugin:2.1.0'
            classpath 'com.android.tools.build:gradle:3.5.3'
            classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        }
    }

    allprojects {
        repositories {
            google()
            jcenter()

        }
    }

    task clean(type: Delete) {
        delete rootProject.buildDir
    }

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

apply plugin: "androidx.navigation.safeargs.kotlin"

apply plugin: 'kotlin-kapt'

android {

    packagingOptions {
        exclude 'META-INF/atomicfu.kotlin_module'
    }

    compileSdkVersion 29
    buildToolsVersion "29.0.2"
    defaultConfig {
        applicationId "com.example.pomoplay"
        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'
        }
    }
}

dependencies {

    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.core:core-ktx:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'androidx.lifecycle:lifecycle-extensions:2.1.0'
    implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.1.0'
    implementation 'com.google.android.material:material:1.0.0'
    implementation 'androidx.navigation:navigation-fragment-ktx:2.1.0'
    implementation 'androidx.navigation:navigation-ui-ktx:2.1.0'

    //Room Components
    implementation "androidx.room:room-runtime:2.2.3"
    kapt "androidx.room:room-compiler:2.2.3"

    //Testing Components
    testImplementation 'junit:junit:4.13'
    androidTestImplementation 'androidx.test:runner:1.2.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'

}

Answer 1

不需要创建单独的数据类。只需确保其serializable

在花了一天时间处理这个错误之后，我发现问题是@Entity类中存在一个空构造函数。

constructor() {}

并不是总是不存在这个构造函数。我有另一个@Entity类，它是非常需要的，否则它会失败，出现以下错误

Entities and POJOs must have a usable public constructor. 
You can have an empty constructor or a constructor whose parameters match the fields (by name and type).
public final class Question implements java.io.Serializable