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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