Android Programming Lecture 15 11/2/2011

Transcription

1 Android Programming Lecture 15 11/2/2011

2 City Web Service Documentation: Need a web services client library: KSOAP2 Acts as our function calling proxy Allows us to generate SOAP envelope, SOAP request, and mail the envelope & request Generates the XML for us

3 KSOAP2 KSOAP2 Documentation: Comes in a JAR file you can add to your project I will upload the JAR file to our tumblr website Import using: Your Project > right click > Import > File System > yourjar.jar Your Project > right click > Properties > Java Build Path > Libraries > Add Jar > yourjar.jar

4 City WebService Client I have built a Java class which abstracts away the details of dealing with KSOAP2 Employ as is, or tweak as necessary See code in Eclipse Usage: CityWebServiceClient webserviceclient = new CityWebServiceClient(); String queryresponse = webserviceclient.getworkordersxml(latitude,longitude,radiusin Feet); // parse the query response by hand or using DOM parser

5 Databases Databases provide support for structured data A collection of tables, which are each a collection of sets of typed values Use a special language that enable searches SQL (among others) File representation and search algorithms to allow efficient retrieval Mechanisms to support transactions Persistent storage

6 Database A database is composed of one or more tables A table is a collection of rows of data (values) structured according to typed columns (attributes) StudentID (int) LastName (String) FirstName (String) Turkett William Doe John Smith Jane StudentID (int) Major (String) Computer Science Math English Undecided

7 Database Tables Information in tables can be linked by shared attributes In the example below, tables share StudentID StudentID (int) LastName (String) FirstName (String) Turkett William Doe John Smith Jane StudentID (int) Major (String) Computer Science Math English Undecided Smith Jane English

8 Database Tables In many ways, database tables map to: class definitions/typed variables XML structure Meals table ID (int) Main (String) Side (String) Drink (String) Price (double) 1 Hamburger French fries Coke Chicken French fries Sprite 4.99 sandwich 3 Cheeseburger Onion rings Diet Coke 4.09

9 Android Database Android uses the SQLite database Small (< 300 Kb) C library Embedded directly as part of application instead of client server Also employed On iphone/ipod Touch/several MP3 players Within Chrome, Mozilla, and Opera As part of Skype

10 Database Tables Three key issues we will need to be concerned with: Creation of database and database structure Inserting and removing data from tables Selecting data from tables

11 Creating A Database Two steps: Creation of the database file Provide a name Creation of tables in that database Give a name Also requires specifying attribute (column) names and types Need to define a primary key unique, not null on each row

12 Creating A Database: Meals Example To continue with the Meals example: Need a Meals table Need five columns: ID: int, Main: String, Side: String, Drink: String, Price: double The ID field will be our primary key (Thought question: Appropriate primary key for student database? For US Citizens?)

13 Creating A Database: Meals Example Creating the database: SQLite databasevariable = openorcreatedatabase(string name, int flagonhowtoopen, CursorFactory cursorfactory);

14 Creating A Database: Meals Example Creating the database: Limit database access to just the creating app No CursorFactory Meaning we are Using the standard SQLite cursor (you can extend Cursor to develop your own that handles result set differently)

15 Creating a Database: Table Creation Need to generate the appropriate SQL statement to create database: create table if not exists TABLENAME (column1name column1type, column2name column2type, ) Types: int for integers, real for doubles, text for String Modifiers: primary key can be added after one entry not null can be added after any entry Then, ask the database to directly execute this SQL statement using it s execsql method, which takes a single String SQL statement

16 Creating a Database: Table Creation Meals Example String createstring = "create table if not exists MEALS (id integer primary key, main text not null, side text, drink text, price real);"; mealsdatabase.execsql(createstring);

17 Creating a Database: Inserting Information Inserting information employs the insert method of the database class Data is stored in a ContentValues object, and it is that object which is used with insert ContentValues is attribute value pairs (again!) Very much like a Bundle or Extras

18 Creating a Database: Inserting Information, Meals Example Create a new ContentValues object, using ContentValue constructor Call put on the object, storing a string as the key, and then the appropriately typed data as the value Call the insert function on the database as follows: databasename.insert(tablename, null, contentvaluesvariable); The null says we don t need to use the NullColumn hack (don t worry about it!)

19 Creating a Database: Selecting Information Selecting information employs the query function of the database object Returns a Cursor, which is essentially an iterator over the returned values out of the table Actually, it holds references to the values in the table Use getxxx methods to extract data from Cursor

20 Creating a Database: Selecting Information: Query query function takes a lot of parameters: (book page 215) A boolean indicating whether want only unique answers String name of table to query A projection (array of strings) that lists columns of interest A where clause string that limits what data is returned (constrains based on value), supports wildcards (looks like: attribute comparison value) An array of strings that can be used to list wildcard substitutions A group by string clause that says whether certain rows should be returned together (usually used with an aggregate function (such as SUM)) A having string filter that constrains which groups to return (used with group by) A string on which column and which ordering to use to order the data A string optional number of rows limit Besides the first two, the others can be left as null and you will effectively retrieve the whole table queried. The where clause is how you strategically define what you want to get out

21 Creating a Database: Selecting Information: Cursors A Cursor has the ability to: (page 211 of textbook) scroll back and forth over the returned values ask about state of cursor in results access data in the results Movement: movetofirst() movetonext() movetoprevious() movetoposition() getposition() Results meta information: getcount() getcolumnname(int index) getcolumnnames() getcolumnindexorthrow(string name) Data access: getfloat(int index) getint(int index) getstring(int index)

22 Creating a Database: Selecting Information: Meals Example Retrieve all and print all but index data from Meals database:

23 Creating a Database: Selecting Information: Meals Example Only print main components of meals over $4.00, sorted by descending price Use a where clause to indicate only want rows where price > 4.00 Use an order clause indicating by price descending Project onto just the main column

24 Other Database Commands Update row(s) in a table Create ContentValue Stuff with columns wantto update Use a where clause to indicate what row(s) to update Call update function databasevariable.update(string tablename, ContentValue newvalues, String whereclause, String[] whereclausewildcardsubstitutions)

25 Other Database Commands Delete rows in a table: Provide a where clause indicating what to delete databasevariable.delete (String tablename, String whereclause, String[] whereclausewildcardsubstitutions)

26 Big Picture Most of the database functions are just abstracting out parts of the SQL language!