Android SQLite database operation (top)

The Android system comes with a database called SQLite. In this article we use a demo to illustrate an example of an Android operating database.

by the

The database files created by Android are stored under the/data/data/< package name >/database, and the suffix is typically xxx.db

See the database file, we generally use a visual tool called SQLite Expert to view.

Let's take a simple example to create a data database that creates a table.

Note that while we have packaged APIs available in Android Development, SQL statements are best mastered.

Let's look at the picture first.

, the following is an open interface with SQLite expert, after running the app, click on the button will create a database named people, the database has a girl table. (If the table is not created, there is also a table below the data, which is the system automatically generated table, but we do not care.) ）

And then look at the code

Layout file Activity_main.xml

<LinearLayoutxmlns:android= "Http://schemas.android.com/apk/res/android"Xmlns:tools= "Http://schemas.android.com/tools"Android:layout_width= "Match_parent"Android:layout_height= "Match_parent"Android:paddingbottom= "@dimen/activity_vertical_margin"Android:paddingleft= "@dimen/activity_horizontal_margin"Android:paddingright= "@dimen/activity_horizontal_margin"Android:paddingtop= "@dimen/activity_vertical_margin"android:orientation= "vertical"Tools:context= "Com.example.db.MainActivity" >    <ButtonAndroid:onclick= "Create_datebase"Android:layout_width= "Match_parent"Android:layout_height= "Wrap_content"Android:text= "Create datebase" /></LinearLayout>

Java files

Mainactivity.java

 Packagecom.example.db;Importandroid.app.Activity;ImportAndroid.os.Bundle;ImportAndroid.view.View; Public classMainactivityextendsActivity {PrivateMysqlite Mydatebasehelper; @Overrideprotected voidonCreate (Bundle savedinstancestate) {Super. OnCreate (savedinstancestate);                Setcontentview (R.layout.activity_main); Mydatebasehelper=NewMysqlite ( This, "People.db",NULL, 1); }         Public voidCreate_datebase (View v) {/** If the database is not created, create and obtain a writable (and actually readable) database if the database is created, get a writable (and actually readable) database * Path data/data/database/people.db */mydatebasehelper.getwritabledatabase (); }}

Mysqlite.java

 Packagecom.example.db;ImportAndroid.content.Context;Importandroid.database.sqlite.SQLiteDatabase;Importandroid.database.sqlite.SQLiteDatabase.CursorFactory;ImportAndroid.database.sqlite.SQLiteOpenHelper;ImportAndroid.widget.Toast;//creating Sqllite requires inheriting the Sqliteopenhelper class abstract class Public classMysqliteextendssqliteopenhelper{ Public Static FinalString create_girl = "CREATE table gril (_id integer primary key Autoincrement,name char (), Age Integer,phone char (20))" ; PrivateContext Mcontext; /** Construction Method parameter Description * First: Incoming context object * Second: The name of the database to be created * Third: Oil standard factory, the introduction of oil target object, is actually a pointer function. Similar to the ResultSet function, this parameter typically passes in NULL * Fourth: Database version number, which is called when upgrading.     The version number must be greater than 1 * Construction method four parameters passed in is actually called to the parent class. * */     PublicMysqlite (Context context, String name, Cursorfactory factory,intversion) {        Super(context, name, Factory, version); //TODO auto-generated Constructor stubMcontext =context; }    //This method is called when the database is created@Override Public voidonCreate (Sqlitedatabase db) {//TODO auto-generated Method Stub        /*Db.execsql (Create_book); Toast.maketext (Mcontext, "Create successded", 0). Show ();*/Db.execsql (Create_girl); Toast.maketext (Mcontext,"Create successded", 0). Show (); }    //called when the database is upgraded@Override Public voidOnupgrade (Sqlitedatabase db,intOldversion,intnewversion) {        //TODO auto-generated Method Stub            }}

Android SQLite database operation (top)