SQLite learning notes, sqlite Learning

SQLite learning notes, sqlite Learning

1: Create a DB. java inherited from SQLiteOpenHelper

package com.example.sqlite;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteDatabase.CursorFactory;import android.database.sqlite.SQLiteOpenHelper;public class DB extends SQLiteOpenHelper {private String sql = "create table person("+"id integer primary key autoincrement,"+"name text,"+"age integer)" ;public DB(Context context, String name, CursorFactory factory,int version) {super(context, name, factory, version);}@Overridepublic void onCreate(SQLiteDatabase db) {db.execSQL(sql);}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {// TODO Auto-generated method stub}}

MainActivity. java

Package com. example. sqlite; import android. content. contentValues; import android. database. cursor; import android. database. sqlite. SQLiteDatabase; import android. database. sqlite. SQLiteOpenHelper; import android. OS. bundle; import android. support. v7.app. actionBarActivity; import android. widget. textView; import android. widget. toast; public class MainActivity extends ActionBarActivity {private TextView text; priv Ate SQLiteDatabase database = null; @ Overrideprotected void onCreate (Bundle savedInstanceState) {super. onCreate (savedInstanceState); setContentView (R. layout. activity_main); this. text = (TextView) findViewById (R. id. text); SQLiteOpenHelper helper = new DB (this, "test. db ", null, 1); database = helper. getWritableDatabase (); // start to test the written function. // first, add five pieces of data for (int I = 0; I <5; I ++) {ContentValues values = new ContentV Alues (); values. put ("name", "insert data"); values. put ("age", I + 20); insert ("person", values);} delete ("delete from person where age> 23 "); // Delete Cursor cursor = query ("select * from person"); // showData (cursor ); // display data ContentValues values = new ContentValues (); values. put ("name", "test update method"); values. put ("age", 6666); update ("person", values, "age =? ", New String [] {" 21 "}); // set 6666 showData (cursor); cursor for all ages 21. close (); database. close ();}/** @ param tableName table name * @ param values dataset */private void insert (String tableName, ContentValues values) {if (database! = Null) {database. insert (tableName, null, values); // Of course, you can also use database.exe SQL (SQL statement execution)} else {Toast. makeText (this, "database object has not been instantiated !! ", Toast. LENGTH_LONG). show () ;}/ ** delete data based on SQL statements */private void delete (String SQL) {if (database! = Null) Export database.exe cSQL (SQL); // Of course, you can also use database.exe SQL (SQL statement execution)} else {Toast. makeText (this, "the database object has not been instantiated !! ", Toast. LENGTH_LONG ). show () ;}}/** query statement, returns a Cursor */private Cursor query (String SQL) {cursor Cursor = database. rawQuery (SQL, null); return cursor;}/** Change Data */private void update (String table, ContentValues values, String whereClause, String [] whereArgs) {if (database! = Null) {database. update (table, values, whereClause, whereArgs); // you can also use database.exe SQL (SQL statement execution)} else {Toast. makeText (this, "the database object has not been instantiated !! ", Toast. LENGTH_LONG ). show () ;}}/** show all data */private void showData (Cursor cursor) {while (cursor. moveToNext () {int nameColumn = cursor. getColumnIndex ("name"); int ageColumn = cursor. getColumnIndex ("age"); String name = cursor. getString (nameColumn); int age = cursor. getInt (ageColumn); this. text. append ("name:" + name + "age:" + age + "\ n");} this. text. append ("all data query is complete! ");}}