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昨天我们制作的项目只要一重新启动,新添加的数据就会丢失,这就需要数据持久化。有两种方法,第一种是通过UrlHttpConnection的POST方法把数据上传给网站的服务器,由网站后端工作人员添加进数据库,这种方法不关前端的事就不学了。我们要学习的是第二种方法,利用手机自己的数据库把数据存放进手机。
因为昨天的项目有点大,帖子太长不利于我们学习,今天新建个项目来学习数据库,项目建好后修改activity_main.xml文件:- <?xml version="1.0" encoding="utf-8"?>
- <LinearLayout 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:orientation="vertical"
- tools:context="com.example.xinwei.databasekotlin.MainActivity">
- <Button
- android:id="@+id/idbutton"
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
- android:text="创建数据库并插入数据"/>
- </LinearLayout>
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然后在MainActivity.kt旁新建createDatabase.kt文件:
- package com.example.xinwei.databasekotlin
- import android.content.Context
- import android.database.sqlite.SQLiteDatabase
- import android.database.sqlite.SQLiteOpenHelper
- import android.widget.Toast
- data class MyData(val name:String,val age:String,val gent:String)
- var dummyDataArray=ArrayList<MyData>()
- val CREATE_MYDATABASE:String="create table if not exists MyTable("+
- "id integer primary key autoincrement,"+
- "name text,"+
- "age text,"+
- "gent text)"
- class CreateDatabase(context:Context, name: String?, factory: SQLiteDatabase.CursorFactory?, version: Int): SQLiteOpenHelper(context, name, factory, version) {
- val context=context
- override fun onCreate(p0: SQLiteDatabase?) {
- p0!!.execSQL(CREATE_MYDATABASE)
- Toast.makeText(context,"数据库创建成功",Toast.LENGTH_SHORT).show()
- }
- override fun onUpgrade(p0: SQLiteDatabase?, p1: Int, p2: Int) {
- TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
- }
- }
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再修改MainActivity.kt文件:
- package com.example.xinwei.databasekotlin
- import android.content.ContentValues
- import android.database.sqlite.SQLiteDatabase
- import android.support.v7.app.AppCompatActivity
- import android.os.Bundle
- import android.widget.Toast
- import kotlinx.android.synthetic.main.activity_main.*
- class MainActivity : AppCompatActivity() {
- var myDatabase:SQLiteDatabase?=null
- var contentValues=ContentValues()
- override fun onCreate(savedInstanceState: Bundle?) {
- super.onCreate(savedInstanceState)
- setContentView(R.layout.activity_main)
- val myDatabaseHelper=CreateDatabase(this,"myDatabase",null,1)
- idbutton.setOnClickListener {
- dummyDataArray.add(MyData("小甲鱼","30","男"))
- dummyDataArray.add(MyData("不二如是","18","男"))
- dummyDataArray.add(MyData("alltolove","37","男"))
- myDatabase=myDatabaseHelper.writableDatabase
- insertValues(0)
- insertValues(1)
- insertValues(2)
- }
- }
- fun insertValues(id:Int){
- contentValues.put("name",dummyDataArray[id].name)
- contentValues.put("age",dummyDataArray[id].age)
- contentValues.put("gent",dummyDataArray[id].gent)
- myDatabase!!.insert("MyTable","",contentValues)
- contentValues.clear()
- Toast.makeText(this,"数据已添加",Toast.LENGTH_SHORT).show()
- }
- }
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这就是我们建数据库的程序,我为了省事就做了模拟从网上抓取的数据,一点击按钮就添加进了数据库。 |
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