Android Application Development-sqliteopenhelper manages SQLite databases and listview

1. sqliteopenhelper introduction:

A helper class to manage database creation and version management.

That is to say, sqliteopenhelper is used to manage the versions used to create and manage a database.

In the class that inherits sqliteopenhelper (extends SQLiteOpenHelper), ThroughRewriteonCreate(SQLiteDatabase),onUpgrade(SQLiteDatabase,
int, int)AndonOpen(SQLiteDatabase)(Optional.

Create a datebase helper class:

Public class databasehelper extends sqliteopenhelper {Private Static final int database_version = 1; string database_create = "create table user (_ id integer primary key autoincrement, mtext varchar (8000 ), mtime varchar (200) "; // constructor public databasehelper (context, string database_name) {super (context, database_name, null, database_version );} @ overridepublic void oncreate (sqlitedatabase dB) {// todo auto-generated method stubsystem. out. println ("create my idea. SQL "); // you can create two tables, db.exe csql (database_create); // important. This is called only when the database is created for the first time, you can also delete the created database before calling // db.exe csql (database_create1);} @ overridepublic void onupgrade (sqlitedatabase dB, int oldversion, int newversion) again) {// todo auto-generated method stubsystem. out. println ("update a database ");}

2. perform database operations in activity:

// Add public void adddata () {contentvalues values = new contentvalues (); // values. put ("ID", 1); // The default _ id used to construct a table is used here, So values can be omitted in this sentence. put ("mtext", "name"); values. put ("mtime", "idea.com"); sqlitedatabase DB = dbhelper. getwritabledatabase (); long rowid = dB. insert ("user", null, values); // insert data in the table and return the _ idsystem. out. println ("-->" + rowid); // mlayout. postinvalidate (); dB. close () ;}// query data public void quer Y () {sqlitedatabase DB = dbhelper. getreadabledatabase (); cursor = dB. query ("user", null, null); While (cursor. movetonext () {string mtext = cursor. getstring (cursor. getcolumnindex ("mtext"); string mtime = cursor. getstring (cursor. getcolumnindex ("mtime"); system. out. println ("" + cursor. getint (cursor. getcolumnindex ("_ id"); system. out. println ("query --->" + mtext + "" + Mt IME);} dB. close () ;}// update public void updatadata () {sqlitedatabase DB = dbhelper. getwritabledatabase (); contentvalues values = new contentvalues (); values. put ("mtext", "name1"); values. put ("mtime", "258963"); dB. update ("user", values, "_ id =? ", New string [] {" 4 "}); // update the data whose _ id is 4 // dB. update ("users", values, null, null); // update all the databases in the table. close () ;}// Delete the specified record public void deletedata () {sqlitedatabase DB = dbhelper. getreadabledatabase (); // delete all table data // dB. delete ("users", null, null); // delete a specified piece of data from the table db.exe csql ("delete from" + "user" + "where _ id =" + integer. tostring (2); dB. close () ;}// Delete the table or the whole database Public void deletetable () {sqlitedatabase DB = dbhelper. getreadabledatabase (); try {// Execute SQL sentence db.exe csql ("Drop table user"); // Delete table} catch (sqlexception e) {} This. deletedatabase ("idea. SQL "); // delete a database. If the database exists, enter the database name to delete the database. close ();}

3. listview operations

Main. xml

<ListView        android:paddingTop="30dp"        android:id="@+id/mlistview"        android:layout_width="fill_parent"        android:layout_height="fill_parent" />

Listviewitem. xml

<?xml version="1.0" encoding="utf-8"?><TableLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:stretchColumns="1"    android:shrinkColumns="1,2" >    <TableRow>        <TextView            android:id="@+id/ItemText"            android:text="TItemTitle"            android:layout_width="320dp"            android:layout_height="36dp"            android:textSize="25dp"            android:layout_gravity="left"            android:gravity="left"            android:paddingLeft="10dp" />        <TextView            android:id="@+id/ItemTime"            android:text="ItemTime"            android:textSize="25dp"             android:layout_width="260dp"            android:layout_height="36dp"            android:layout_gravity="right"            android:gravity="left"            android:paddingRight="10dp"/>    </TableRow></TableLayout>

Add to listview when querying data

Variable declaration:

private ListView mlistview;private SimpleAdapter mlistItemAdapter;private ArrayList<HashMap<String, Object>> mlistItem = null;private DatabaseHelper dbHelper;

Add:

Mlistview = (listview) findviewbyid (R. id. mlistview); mlistitem = new arraylist