Android Kotlin使用SQLite案例详解

kotlin使用sqlite

首先确定我们的目标，sqlite只是一种工具，我们需要掌握就是增删改查就可以，我们真正需要动脑的还是项目中的业务逻辑。我这篇文章写得比较适合新手，没用过sqlite的同学。
前期准备工作
新建一个类mydatabasehelper继承自sqliteopenhelper，代码如下：

class mydatabasehelper(var context: context, name: string, version: int) :
    sqliteopenhelper(context, name, null, version) {
    public var createbook="create table book (" +
            "id integer primary key autoincrement," +
            "author text," +
            "price real," +
            "pages integer," +
            "name text)"

    override fun oncreate(db: sqlitedatabase?) {
//        下面这个todo 如果不注释掉的话就会报错。
//        todo("not implemented") //to change body of created functions use file | settings | file templates.
        db?.execsql(createbook)
        toast.maketext(context,"create successed",toast.length_long).show()
    }

    override fun onupgrade(db: sqlitedatabase?, oldversion: int, newversion: int) {
//        todo("not implemented") //to change body of created functions use file | settings | file templates.
        db?.execsql("drop table if exists book")
        oncreate(db)
    }
}

对数据进行操作
操作比较简单，下面直接看代码:
activity中

class mysqlite : appcompatactivity() {

    override fun oncreate(savedinstancestate: bundle?) {
        super.oncreate(savedinstancestate)
        setcontentview(r.layout.activity_my_sqlite)
        val dbhelper=mydatabasehelper(this,"bookstore.db",1)
        /**
         * 创建表
         */
        btncreatedatabase.setonclicklistener {
            dbhelper.writabledatabase
        }
        /**
         * 添加数据
         */
        btnadddata.setonclicklistener {
            val db=dbhelper.writabledatabase
            val values1=contentvalues().apply {
//                第一条数据
                put("name","the da vinci code")
                put("author","dan broen")
                put("pages",454)
                put("price",16.96)
            }
            db.insert("book",null,values1)
            val  values2=contentvalues().apply {
//                第二条数据
                put("name","the lost symbol")
                put("author","dan brown")
                put("pages",510)
                put("price",19.95)
            }
            db.insert("book",null,values2)
        }
        btnupdatedata.setonclicklistener {
            val db=dbhelper.writabledatabase
            val values=contentvalues()
            values.put("price",10.99)
            db.update("book",values,"name=?", arrayof("the da vinci code"))
        }
        btndeletedata.setonclicklistener {
            val db=dbhelper.writabledatabase
            db.delete("book","pages>?", arrayof("500"))
        }
        btnquerydata.setonclicklistener {
            val db=dbhelper.writabledatabase
//            查询book表中所有数据
//            这里获取到是cursor对象
            val cursor=db.query("book",null,null,null,null,null,null)
            if (cursor.movetofirst()){
                do {
                    val name=cursor.getstring(cursor.getcolumnindex("name"))
                    val author=cursor.getstring(cursor.getcolumnindex("author"))
                    val pages=cursor.getstring(cursor.getcolumnindex("pages"))
                    val price=cursor.getstring(cursor.getcolumnindex("price"))
                    log.d("mainactivity","book name is $name")
                    log.d("mainactivity","author is $author")
                    log.d("mainactivity","pages is $pages")
                    log.d("mainactivity","price is $price")
                }while (cursor.movetonext())
            }
            cursor.close()
        }
    }
}

布局文件

<?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"
    tools:context=".sqlite.mysqlite">

    <button
        android:id="@+id/btncreatedatabase"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="createdatabase"
        android:textallcaps="false"
        app:layout_constrainttop_totopof="parent" />

    <button
        android:id="@+id/btnadddata"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="adddata"
        android:textallcaps="false"
        app:layout_constrainttop_tobottomof="@+id/btncreatedatabase" />

    <button
        android:id="@+id/btnupdatedata"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="updatedata"
        android:textallcaps="false"
        app:layout_constrainttop_tobottomof="@+id/btnadddata" />

    <button
        android:id="@+id/btndeletedata"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="deletedata"
        app:layout_constrainttop_tobottomof="@+id/btnupdatedata" />

    <button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/btnquerydata"
        android:text="query data"
        android:textallcaps="false"
        app:layout_constrainttop_tobottomof="@+id/btndeletedata"/>
</androidx.constraintlayout.widget.constraintlayout>

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