帮我优化下面代码： package com.heytea.android_syrup; import android.app.Application import androidx.room.Room import androidx.room.RoomDatabase import androidx.room.migration.Migration import androidx.sqlite.db.SupportSQLiteDatabase object DatabaseManager{ private const val DB_NAME="syrup.db" private val MIGRATIONS = arrayOf(Migration1) private lateinit var application: Application val db:AppDatabase by lazy { Room.databaseBuilder(application.applicationContext,AppDatabase::class.java, DB_NAME) .allowMainThreadQueries() .build() } fun saveApplication(application: Application){ this.application=application } private object CreatedCallBack : RoomDatabase.Callback() { override fun onCreate(db: SupportSQLiteDatabase) { MIGRATIONS.map { } } } private object Migration1:Migration(1,2){ override fun migrate(database: SupportSQLiteDatabase) { } } }

下面是对代码的优化建议：

1. 将 object DatabaseManager 中的属性和方法都改成类的形式，并且添加 constructor 构造函数，这样代码更加规范。

2. 将 MIGRATIONS 和 CreatedCallBack 改成内部类，这样可以更好地隐藏实现细节。

3. 在构造函数中将 application 作为参数传入，这样可以避免使用全局变量。

4. 在 onCreate 方法中添加循环遍历 MIGRATIONS 的逻辑，这样可以自动执行所有的 Migration。

5. 将 Migration1 中的具体迁移逻辑补充完整。

下面是优化后的代码：

package com.heytea.android_syrup

import android.app.Application
import androidx.room.Room
import androidx.room.RoomDatabase
import androidx.room.migration.Migration
import androidx.sqlite.db.SupportSQLiteDatabase

class DatabaseManager private constructor(private val application: Application) {

    companion object {
        private const val DB_NAME = "syrup.db"
        private val MIGRATIONS = arrayOf(Migration1)

        @Volatile
        private var INSTANCE: DatabaseManager? = null

        fun getInstance(application: Application): DatabaseManager {
            return INSTANCE ?: synchronized(this) {
                INSTANCE ?: DatabaseManager(application).also {
                    INSTANCE = it
                }
            }
        }
    }

    val db: AppDatabase by lazy {
        Room.databaseBuilder(
            application.applicationContext,
            AppDatabase::class.java,
            DB_NAME
        ).allowMainThreadQueries()
            .addMigrations(*MIGRATIONS)
            .build()
    }

    private object CreatedCallBack : RoomDatabase.Callback() {
        override fun onCreate(db: SupportSQLiteDatabase) {
            MIGRATIONS.forEach { migration ->
                migration.migrate(db)
            }
        }
    }

    private class Migration1 : Migration(1, 2) {
        override fun migrate(database: SupportSQLiteDatabase) {
            // TODO: 添加具体的迁移逻辑
        }
    }
}