Quitting Persistence, Multiview Applications

CS185c

Chris Pollett

Sep. 30, 2009

Outline

Android Database Persistence
iPhone Multiview Applications

Introduction

On Monday, we introduced SQLite which is a library which is available for both iPhone and Android.
We showed how to use this library when coding on the iPhone.
Today, we show how to use this library from within Android.

Android Database Persistence

To test out our database code we need to import the following packages:

import android.database.sqlite.*;
import android.database.*;
import android.content.*;
import android.util.*;

We will make use of two important classes:
- SQLiteOpenHelper - an abstract class whose onCreate and onUpgrade methods need to be implemented. Objects of this class are used to open/create the database
- SQLiteDatabase - objects of this class encapsulate a particular database and allow us to manipulate it.

On Testing Code

The following code just writes to the log file based on our SQL test.
We put it in the onCreate method of a dummy testing activity.

dbOpenHelper and db were private instance variables of our class.

dbOpenHelper = new DBOpenHelper(this, "My_Database", 3);
        
db = dbOpenHelper.getWritableDatabase();
        
//insert into database

db.execSQL("INSERT OR REPLACE INTO PEOPLE VALUES (5, 'test')");
db.close();
        
dbOpenHelper = new DBOpenHelper(this, "My_Database", 3);
        
db = dbOpenHelper.getReadableDatabase();
Cursor c = db.rawQuery("SELECT * FROM PEOPLE", null);

    	
for(int i=0; i< c.getCount(); i++)
{
   c.moveToNext();
   Log.i("SqliteAndroid", "Id="+c.getInt(0));
   Log.i("SqliteAndroid", "Hobby="+c.getString(1));        	
}
        
        
db.close();

Subclassing SQLiteOpenHelper

We subclasses SQLiteOpenHelper as an inner class of our test activity

Here is the code:

    private static class DBOpenHelper extends SQLiteOpenHelper
    {
       public DBOpenHelper(Context context, String dbName, int version )
       {
    	  // third argument id to a cursor factory -- we don't care about
    	  super(context, dbName, null, version);
       }
       
       @Override
       public void onCreate(SQLiteDatabase db)
       {
    	   try
    	   {
    		  db.execSQL("CREATE TABLE IF NOT EXISTS PEOPLE (ID INTEGER PRIMARY KEY, HOBBY TEXT)"); 
    	   }
    	   catch(SQLException e)
    	   {
    		  Log.e("SqliteAndroid", "DBOpenHelper", e);
    	   }
       }
       
       @Override
       public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
       {
    	  db.execSQL("DROP TABLE IF EXISTS PEOPLE");
    	  this.onCreate(db);
       }
    }

Multiview Applications

We are now going to consider iPhone Applications that have more than one view.
An example of using multiviews is a utility application such as the Stock application that ships with the iPhone.
This application has a primary view that displays current stock prices.
If one clicks the 'i' in the lower right corner of this view it displays a second view which allows one to picks which stocks to follow and what format quotes should be in.
Another kind of multiview application is one involving a tab bar at the bottom of the screen.
For example, the phone application has a tab bar with Favorites, Recents, Contacts, Keypad, and Voicemail on it. Select one of these switched between views.
The Mail app uses a third kind of multiview where one has a navigation bar at the top of the screen to switch between views.

More on Multiview Applications

Each multiview application uses a specific controller class from UIKit.
Tab bar interfaces are implemented using the class UITabBarController and navigation interfaces using UINavigationController.
We are going to create a view with a bar on the bottom with the button "Switch Views".
The initial view will have a blue background with a button "Press me" centered on it.
Clicking "Switch Views" will switch to a second view with the same kind of bar on the bottom, but with a button with "Press Me, Too" on it.
One things that is different between these kind of app and those we've considered before is that each view will have its own controller.
To build our switcher, we will first create a new Window-Based Application.

Creating Our View Controller and Nib Files

A Window-based Application just has a MainWindow.xib file (no other NIB files).
It also only has its class folder the application delegate class.
The first thing we are going to do is to add the UIViewController subclasses for our two views.
To do this we go to Groups & Files and select New File... from the File menu.
We use the UIViewController template under the Cocoa Touch Class to set up these controllers and give them the names: SwitchViewController, YellowViewController, and BlueViewController.
Next we use the View XIB template under User Interface to create two views: BlueView.xib and YellowView.xib
Finally, we start hooking these files together.

Modifying the App Delegate Header

We next modify the header class of multiview app delegate class as follows:

@class SwitchViewController;

@interface multiviewdemoAppDelegate : NSObject  {
    IBOutlet UIWindow *window;
    IBOutlet SwitchViewController *switchViewController;
}

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet SwitchViewController *switchViewController;

@end

Basically, what we done is added an outlet for our SwitchViewController. This will serve as a hook into the new views we've created.

Modifying the App Delegate Implementation

We next modify the implementation file as follows:

#import "multiviewdemoAppDelegate.h"
#import "SwitchViewController.h"

@implementation multiviewdemoAppDelegate

@synthesize window;
@synthesize switchViewController;

- (void)applicationDidFinishLaunching:(UIApplication *)application {    

    // Override point for customization after application launch
    [window addSubview:switchViewController.view];
    [window makeKeyAndVisible];
}


- (void)dealloc {
    [window release];
    [switchViewController release];
    [super dealloc];
}


@end

Besides adding the appropriate @synthesize, the main thing we change is to add a sub view to the window.

SwitchViewController.h

Now we start writing our controllers today (will finish next day):

#import <UIKit/UIKit.h>

@class BlueViewController;
@class YellowViewController;

@interface SwitchViewController : UIViewController {
	YellowViewController *yellowViewController;
	BlueViewController *blueViewController;
	
}

@property (retain, nonatomic) YellowViewController *yellowViewController;
@property (retain, nonatomic) BlueViewController *blueViewController;

-(IBAction) switchViews:(id) sender;

@end