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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