个性化阅读
专注于IT技术分析
        找回密码
当前位置：srcmini > Kotlin > 正文

Kotlin Android SQLite教程

2020-03-09 03:23:35 分类：Kotlin 阅读(1047) 评论(0)

本文概述

SQLite是一个开放源代码关系数据库, 用于在Android设备上执行数据库操作, 例如从数据库中存储, 操作或检索持久性数据。

默认情况下, SQLite数据库嵌入在android中。因此, 无需执行任何数据库设置或管理任务。

SQLiteOpenHelper类提供使用SQLite数据库的功能。

SQLiteOpenHelper类

android.database.sqlite.SQLiteOpenHelper类用于数据库创建和版本管理。为了执行任何数据库操作, 你必须提供SQLiteOpenHelper类的onCreate()和onUpgrade()方法的实现。

SQLiteOpenHelper类的构造方法

SQLiteOpenHelper类有两个构造函数。

建设者 描述
SQLiteOpenHelper（上下文：上下文, 名称：字符串, 工厂：SQLiteDatabase.CursorFactory, 版本：Int） 创建一个SQLiteOpenHelper对象, 用于创建, 打开和管理数据库。
SQLiteOpenHelper（上下文：上下文, 名称：字符串, 工厂：SQLiteDatabase.CursorFactory, 版本：Int, errorHandler：DatabaseErrorHandler） 创建一个SQLiteOpenHelper对象, 用于创建, 打开和管理数据库。它指定错误处理程序。

SQLiteOpenHelper类的方法

SQLiteOpenHelper类中提供了几种方法。下面提到其中一些：

方法 描述
public abstract void onCreate(SQLiteDatabase db) 首次创建数据库时仅调用一次。
public abstract void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 当数据库需要升级时调用。
public synchronized void close () 关闭数据库对象。
public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) 当数据库需要降级时调用。

SQLiteDatabase类

它包含要在SQLite数据库上执行的方法, 例如创建, 更新, 删除, 选择等。

SQLiteDatabase类的方法

SQLiteDatabase类中有许多方法。其中一些如下：

方法 描述
execSQL（String sql）：单位 执行SQL查询, 而不是选择查询。
insert（String table, String nullColumnHack, ContentValues values）：长 在数据库上插入一条记录。该表指定表名, nullColumnHack不允许完全为空值。如果第二个参数为null, 则如果值为空, 则android将存储null值。第三个参数指定要存储的值。
update（String table, ContentValues values, String whereClause, String [] whereArgs）：Int 更新一行。
查询（字符串表, 字符串[]列, 字符串选择, 字符串[] selectionArgs, 字符串groupBy, 具有字符串, 字符串orderBy）：游标 返回结果集上的光标。

Kotlin Android SQLite数据库CRUD示例

在此示例中, 我们将在Android SQLite数据库上执行创建, 读取, 更新和删除操作。

activity_main.xml

在activity_main.xml文件中, 添加以下代码。在此文件中, 我们添加了三个EditText, 一个ListView, 四个用于保存, 查看, 更新和删除操作的Button。

<?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:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:orientation="vertical"
    tools:context="example.srcmini02.com.kotlinsqlitecrud.MainActivity">

<TableLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <TableRow>
        <TextView
            android:text="User Id"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_column="1" />

        <EditText

            android:id="@+id/u_id"
            android:layout_width="200dp"
            android:layout_height="wrap_content"
            android:layout_marginLeft="20sp"
            android:layout_marginStart="20sp"
            android:width="150px" />
    </TableRow>
    <TableRow>
         <TextView
            android:text="User Name"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_column="1" />

        <EditText
            android:id="@+id/u_name"
            android:width="200dp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_column="2"
            android:layout_marginStart="20sp"
            android:layout_marginLeft="20sp"/>
    </TableRow>

    <TableRow>

        <TextView
            android:text="User Email"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_column="1" />

       <EditText
           android:id="@+id/u_email"
            android:width="200dp"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_column="2"
            android:layout_marginStart="20sp"
            android:layout_marginLeft="20sp" />
    </TableRow>

</TableLayout>
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="350sp"
        android:layout_marginTop="20sp">
        <ListView
            android:id="@+id/listView"
            android:layout_width="wrap_content"
            android:layout_height="350sp"/>
    </LinearLayout>
<LinearLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="40sp"
    android:orientation="horizontal"
    android:layout_gravity="center">
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Save"
        android:onClick="saveRecord"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="View"
        android:onClick="viewRecord"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Update"
        android:onClick="updateRecord"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Delete"
        android:onClick="deleteRecord"/>
</LinearLayout>
</LinearLayout>

MainActivity.kt

在MainActivity.kt类中添加以下代码。在此类中, saveRecord()函数保存记录。 viewRecord()函数读取记录并将其显示到ListView中, updateRecord()函数根据id更新记录, 而deleteRecord()函数删除记录。 val databaseHandler：DatabaseHandler = DatabaseHandler（this）创建调用SQLite数据库逻辑的DatabaseHandler类的实例。

package example.srcmini02.com.kotlinsqlitecrud

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.EditText
import android.widget.Toast
import kotlinx.android.synthetic.main.activity_main.*
import android.content.DialogInterface
import android.support.v7.app.AlertDialog


class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
    //method for saving records in database
    fun saveRecord(view: View){
        val id = u_id.text.toString()
        val name = u_name.text.toString()
        val email = u_email.text.toString()
        val databaseHandler: DatabaseHandler= DatabaseHandler(this)
        if(id.trim()!="" && name.trim()!="" && email.trim()!=""){
            val status = databaseHandler.addEmployee(EmpModelClass(Integer.parseInt(id), name, email))
            if(status > -1){
                Toast.makeText(applicationContext, "record save", Toast.LENGTH_LONG).show()
                u_id.text.clear()
                u_name.text.clear()
                u_email.text.clear()
            }
        }else{
            Toast.makeText(applicationContext, "id or name or email cannot be blank", Toast.LENGTH_LONG).show()
        }

    }
    //method for read records from database in ListView
    fun viewRecord(view: View){
        //creating the instance of DatabaseHandler class
        val databaseHandler: DatabaseHandler= DatabaseHandler(this)
        //calling the viewEmployee method of DatabaseHandler class to read the records
        val emp: List<EmpModelClass> = databaseHandler.viewEmployee()
        val empArrayId = Array<String>(emp.size){"0"}
        val empArrayName = Array<String>(emp.size){"null"}
        val empArrayEmail = Array<String>(emp.size){"null"}
        var index = 0
        for(e in emp){
            empArrayId[index] = e.userId.toString()
            empArrayName[index] = e.userName
            empArrayEmail[index] = e.userEmail
            index++
        }
        //creating custom ArrayAdapter
        val myListAdapter = MyListAdapter(this, empArrayId, empArrayName, empArrayEmail)
        listView.adapter = myListAdapter
    }
    //method for updating records based on user id
    fun updateRecord(view: View){
        val dialogBuilder = AlertDialog.Builder(this)
        val inflater = this.layoutInflater
        val dialogView = inflater.inflate(R.layout.update_dialog, null)
        dialogBuilder.setView(dialogView)

        val edtId = dialogView.findViewById(R.id.updateId) as EditText
        val edtName = dialogView.findViewById(R.id.updateName) as EditText
        val edtEmail = dialogView.findViewById(R.id.updateEmail) as EditText

        dialogBuilder.setTitle("Update Record")
        dialogBuilder.setMessage("Enter data below")
        dialogBuilder.setPositiveButton("Update", DialogInterface.OnClickListener { _, _ ->

            val updateId = edtId.text.toString()
            val updateName = edtName.text.toString()
            val updateEmail = edtEmail.text.toString()
            //creating the instance of DatabaseHandler class
            val databaseHandler: DatabaseHandler= DatabaseHandler(this)
            if(updateId.trim()!="" && updateName.trim()!="" && updateEmail.trim()!=""){
                //calling the updateEmployee method of DatabaseHandler class to update record
                val status = databaseHandler.updateEmployee(EmpModelClass(Integer.parseInt(updateId), updateName, updateEmail))
                if(status > -1){
                    Toast.makeText(applicationContext, "record update", Toast.LENGTH_LONG).show()
                }
            }else{
                Toast.makeText(applicationContext, "id or name or email cannot be blank", Toast.LENGTH_LONG).show()
            }

        })
        dialogBuilder.setNegativeButton("Cancel", DialogInterface.OnClickListener { dialog, which ->
            //pass
        })
        val b = dialogBuilder.create()
        b.show()
    }
    //method for deleting records based on id
    fun deleteRecord(view: View){
        //creating AlertDialog for taking user id
        val dialogBuilder = AlertDialog.Builder(this)
        val inflater = this.layoutInflater
        val dialogView = inflater.inflate(R.layout.delete_dialog, null)
        dialogBuilder.setView(dialogView)

        val dltId = dialogView.findViewById(R.id.deleteId) as EditText
        dialogBuilder.setTitle("Delete Record")
        dialogBuilder.setMessage("Enter id below")
        dialogBuilder.setPositiveButton("Delete", DialogInterface.OnClickListener { _, _ ->

            val deleteId = dltId.text.toString()
            //creating the instance of DatabaseHandler class
            val databaseHandler: DatabaseHandler= DatabaseHandler(this)
            if(deleteId.trim()!=""){
                //calling the deleteEmployee method of DatabaseHandler class to delete record
                val status = databaseHandler.deleteEmployee(EmpModelClass(Integer.parseInt(deleteId), "", ""))
                if(status > -1){
                    Toast.makeText(applicationContext, "record deleted", Toast.LENGTH_LONG).show()
                }
            }else{
                Toast.makeText(applicationContext, "id or name or email cannot be blank", Toast.LENGTH_LONG).show()
            }

        })
        dialogBuilder.setNegativeButton("Cancel", DialogInterface.OnClickListener { _, _ ->
            //pass
        })
        val b = dialogBuilder.create()
        b.show()
    }
}

EmpModelClass.kt

创建一个名为EmpModelClass.kt的数据模型类

package example.srcmini02.com.kotlinsqlitecrud
//creating a Data Model Class
class EmpModelClass (var userId: Int, val userName:String , val userEmail: String)

custom_list.xml

创建一个自定义行布局以在ListView中显示列表项。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/linearLayout">

    <TextView
        android:id="@+id/textViewId"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Id"
        android:textAppearance="@style/Base.TextAppearance.AppCompat.Medium"/>

    <TextView
        android:id="@+id/textViewName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Name"
        android:textAppearance="@style/Base.TextAppearance.AppCompat.Medium"/>

    <TextView
        android:id="@+id/textViewEmail"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Email"
        android:textAppearance="@style/Base.TextAppearance.AppCompat.Medium"/>
</LinearLayout>

MyListAdapter.kt

现在, 创建一个名为MyListAdapter.kt的自定义适配器类, 并扩展ArrayAdapter类, 该类将数据模型填充到ListView中。

package example.srcmini02.com.kotlinsqlitecrud

import android.app.Activity
import android.view.View
import android.view.ViewGroup
import android.widget.ArrayAdapter
import android.widget.TextView

class MyListAdapter(private val context: Activity, private val id: Array<String>, private val name: Array<String>, private val email: Array<String>)
    : ArrayAdapter<String>(context, R.layout.custom_list, name) {

    override fun getView(position: Int, view: View?, parent: ViewGroup): View {
        val inflater = context.layoutInflater
        val rowView = inflater.inflate(R.layout.custom_list, null, true)

        val idText = rowView.findViewById(R.id.textViewId) as TextView
        val nameText = rowView.findViewById(R.id.textViewName) as TextView
        val emailText = rowView.findViewById(R.id.textViewEmail) as TextView

        idText.text = "Id: ${id[position]}"
        nameText.text = "Name: ${name[position]}"
        emailText.text = "Email: ${email[position]}"
        return rowView
    }
}

update_dialog.xml

创建用于显示AlertDialog的布局以更新记录。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:padding="10dp"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <EditText
        android:id="@+id/updateId"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="enter id" />

    <EditText
        android:id="@+id/updateName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="enter name"/>

    <EditText
        android:id="@+id/updateEmail"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="enter email"/>
</LinearLayout>

delete_dialog.xml

创建用于显示AlertDialog的布局以删除记录。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:padding="10dp"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <EditText
        android:id="@+id/deleteId"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="enter id" />
</LinearLayout>

DatabaseHandler.kt

创建扩展SQLiteOpenHelper类的DatabaseHandler.kt类, 并覆盖其onCreate(), onUpgrage()函数。通过将ContentValues对象传递给insert()方法, 将数据插入数据库。

package example.srcmini02.com.kotlinsqlitecrud

import android.content.Context
import android.database.sqlite.SQLiteDatabase
import android.database.sqlite.SQLiteOpenHelper
import android.content.ContentValues
import android.database.Cursor
import android.database.sqlite.SQLiteException

//creating the database logic, extending the SQLiteOpenHelper base class
class DatabaseHandler(context: Context): SQLiteOpenHelper(context, DATABASE_NAME, null, DATABASE_VERSION) {
    companion object {
        private val DATABASE_VERSION = 1
        private val DATABASE_NAME = "EmployeeDatabase"
        private val TABLE_CONTACTS = "EmployeeTable"
        private val KEY_ID = "id"
        private val KEY_NAME = "name"
        private val KEY_EMAIL = "email"
    }
    override fun onCreate(db: SQLiteDatabase?) {
       // TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
       //creating table with fields
        val CREATE_CONTACTS_TABLE = ("CREATE TABLE " + TABLE_CONTACTS + "("
                + KEY_ID + " INTEGER PRIMARY KEY, " + KEY_NAME + " TEXT, "
                + KEY_EMAIL + " TEXT" + ")")
        db?.execSQL(CREATE_CONTACTS_TABLE)
    }

    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 " + TABLE_CONTACTS)
        onCreate(db)
    }


    //method to insert data
    fun addEmployee(emp: EmpModelClass):Long{
        val db = this.writableDatabase
        val contentValues = ContentValues()
        contentValues.put(KEY_ID, emp.userId)
        contentValues.put(KEY_NAME, emp.userName) // EmpModelClass Name
        contentValues.put(KEY_EMAIL, emp.userEmail ) // EmpModelClass Phone
        // Inserting Row
        val success = db.insert(TABLE_CONTACTS, null, contentValues)
        //2nd argument is String containing nullColumnHack
        db.close() // Closing database connection
        return success
    }
    //method to read data
    fun viewEmployee():List<EmpModelClass>{
        val empList:ArrayList<EmpModelClass> = ArrayList<EmpModelClass>()
        val selectQuery = "SELECT  * FROM $TABLE_CONTACTS"
        val db = this.readableDatabase
        var cursor: Cursor? = null
        try{
            cursor = db.rawQuery(selectQuery, null)
        }catch (e: SQLiteException) {
            db.execSQL(selectQuery)
            return ArrayList()
        }
        var userId: Int
        var userName: String
        var userEmail: String
        if (cursor.moveToFirst()) {
            do {
                userId = cursor.getInt(cursor.getColumnIndex("id"))
                userName = cursor.getString(cursor.getColumnIndex("name"))
                userEmail = cursor.getString(cursor.getColumnIndex("email"))
                val emp= EmpModelClass(userId = userId, userName = userName, userEmail = userEmail)
                empList.add(emp)
            } while (cursor.moveToNext())
        }
        return empList
    }
    //method to update data
    fun updateEmployee(emp: EmpModelClass):Int{
        val db = this.writableDatabase
        val contentValues = ContentValues()
        contentValues.put(KEY_ID, emp.userId)
        contentValues.put(KEY_NAME, emp.userName) // EmpModelClass Name
        contentValues.put(KEY_EMAIL, emp.userEmail ) // EmpModelClass Email

        // Updating Row
        val success = db.update(TABLE_CONTACTS, contentValues, "id="+emp.userId, null)
        //2nd argument is String containing nullColumnHack
        db.close() // Closing database connection
        return success
    }
    //method to delete data
    fun deleteEmployee(emp: EmpModelClass):Int{
        val db = this.writableDatabase
        val contentValues = ContentValues()
        contentValues.put(KEY_ID, emp.userId) // EmpModelClass UserId
        // Deleting Row
       val success = db.delete(TABLE_CONTACTS, "id="+emp.userId, null)
        //2nd argument is String containing nullColumnHack
        db.close() // Closing database connection
        return success
    }
}

输出：

Kotlin Android SQLite教程
Kotlin Android SQLite教程
Kotlin Android SQLite教程
Kotlin Android SQLite教程
Kotlin Android SQLite教程
Kotlin Android SQLite教程
Kotlin Android SQLite教程
Kotlin Android SQLite教程
Kotlin Android SQLite教程
赞(0)
未经允许不得转载：srcmini » Kotlin Android SQLite教程
标签：

相关推荐

评论 抢沙发

评论前必须登录！

 

猜你喜欢

热门标签

网站开发 (2587)WordPress开发 (2055)WordPress主题 (1517)Web开发 (692)主题 (527)数据科学 (444)教程合集 (317)资源合集 (316)函数 (287)页面 (267)python开发 (261)项目示例 (243)WordPress自定义页面 (233)图像 (219)错误 (213)网站 (189)UX设计 (187)Web安全 (179)模板 (178)Web运维 (177)应用程序 (177)WordPress插件 (176)插件 (171)前端开发 (166)算法 (150)woocommerce (149)数据结构 (149)常见问题 (142)设计 (138)网红 (138)