Android platform application development example: Notepad (1)

In this tutorial, a simple list interface will be created, allowing users to add and delete, but not editing. Includes the following content:

◆ Basic knowledge of ListActivities and how to create menu items.

◆ How to use the SQLite database to access data.

◆ How to use ArrayAdapter to bind data to ListView (the simplest way ).

◆ Basic Layout, including how to display a ListView, how to insert a menu item to a menu, and how to respond to the menu

Step 1 create a project

Use Eclipse to create a project Notepad

Step 2: How to Use the Sqlite Database

The Context class is required for system-related interface calls.

1. Open the database

Code snippet:

Public DBHelper (Context ctx ){ Try { // Open an existing database Db = ctx. openDatabase (DATABASE_NAME, null ); } Catch (FileNotFoundException e ){ Try { // Create a new database Db = Ctx. createDatabase (DATABASE_NAME, DATABASE_VERSION, 0, null ); // Create a data table Db.exe cSQL (DATABASE_CREATE ); } Catch (FileNotFoundException e1 ){ Db = null; } } }

OpenDatabase of the Context class can open an existing database. If the database does not exist, a FileNotFoundException exception will be thrown. You can use the createDatabase function of the Context class to create a new database. Call the execSQL method of SQLiteDatabase to execute an SQL statement to create a new data table.

2. Get the data in the table

The Code is as follows:

Public List <Row> fetchAllRows (){ ArrayList <Row> ret = new ArrayList <Row> (); Try { Cursor c = Db. query (DATABASE_TABLE, new String [] { "Rowid", "title", "body"}, null ); Int numRows = c. count (); C. first (); For (int I = 0; I <numRows; ++ I ){ Row row = new Row (); Row. rowId = c. getLong (0 ); Row. title = c. getString (1 ); Row. body = c. getString (2 ); Ret. add (row ); C. next (); } } Catch (SQLException e ){ Log. e ("booga", e. toString ()); } Return ret; }

Create a Cursor class Cursor to query a table through the query method of SQLiteDatabase. With Cursor, You can traverse all records.

3. Add a new record

Public void createRow (String title, String body ){ ContentValues initialValues = new ContentValues (); InitialValues. put ("title", title ); InitialValues. put ("body", body ); Db. insert (DATABASE_TABLE, null, initialValues ); }

Construct a ContentValues class. You can call the put method to set the attributes of a record. Add a new record by calling the insert method of SQLiteDatabase.

4. delete records

Public void deleteRow (String str) { Db. delete (DATABASE_TABLE, "title = \ '" + str + "\'", null ); }

Directly call the delete method of SQLiteDatabase. The second parameter is an SQL conditional expression.

Step 3: Display Mode and Interface

Most interfaces have a Layout. Our interface is the List displayed in the whole screen. There are other display methods, such as floating window Dialog, Alert ).
Open the main. xml file.
This is a resource file that defines the display style of the interface.

A. All interface resource files start with a line like this: <? Xml version = "1.0" encoding = "UTF-8 "? >.

B. The general type definition is LinearLayout and not always)

C. The definition of XML Namespaces is always the following line:

Xmlns: android = "http://schemas.android.com/apk/res/android"