Android使用LitePal操作SQLite数据库（Kotlin）

MainActivity.kt---->

package com.example.fredric.litepaltest

import android.content.ContentValues
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.widget.Button
import com.example.fredric.litepaltest.bean.Book
import org.litepal.LitePal

class MainActivity : AppCompatActivity() {

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

var createDatabase = findViewById<Button>(R.id.create_database)
createDatabase.setOnClickListener{
LitePal.getDatabase()
}

var addData = findViewById<Button>(R.id.add_data)
addData.setOnClickListener{
var book = Book(null,"Dan Brown","The Da Vinci Code",16.96,454,"Unknown")
book.save()
}

var updateData = findViewById<Button>(R.id.update_data)
updateData.setOnClickListener{
// var book = Book(null,"Dan Brown","The Lost Symbol",19.95,510,"Unknown")
// book.save()
// book.price = 10.99
// book.save()

var values = ContentValues()
values.put("price",14.95)
values.put("press","Anchor")
LitePal.updateAll(Book::class.java,values,"name = ? and author = ?","The Lost Symbol","Dan Brown")
}

var deleteData = findViewById<Button>(R.id.delete_data)
deleteData.setOnClickListener{
LitePal.deleteAll(Book::class.java,"price < ?","15")
}

var queryData = findViewById<Button>(R.id.query_data)
queryData.setOnClickListener{
var books = LitePal.findAll(Book::class.java)
for(book in books) {
Log.d("MainActivity", "book name is :"+ book.name)
Log.d("MainActivity", "book author is :"+ book.author)
Log.d("MainActivity", "book pages is :"+book.pages)
Log.d("MainActivity", "book price is :"+book.price)
Log.d("MainActivity", "book press is :"+book.press)
}
}

}
}

Book.kt-->

package com.example.fredric.litepaltest.bean

import org.litepal.crud.LitePalSupport

data class Book(var id: Int?,var author: String?,var name: String?,var price: Double?,var pages: Int?,var press: String?) :

LitePalSupport()

Category.kt--->

package com.example.fredric.litepaltest.bean

import org.litepal.crud.LitePalSupport

data class Category(

val id: Int?,

val categoryName: String?,

val categoryCode: Int?

) : LitePalSupport()

src/main/assets/litepal.xml--->

<?xml version="1.0" encoding="UTF-8" ?>

<list>

</list>

</litepal>

activity_main.xml--->

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:orientation="vertical"