Jeg har skaffet meg et fantastisk verktøy for å gjøre databaseprogrammering på iPhone som heter Sensible Table View (STV) og er fra Sensible Cocoa.

Men da jeg skulle igang med litt mer avanserte filter og tilhørende summeringer, ble jeg sittende fast, ikke et par timer, men en hel uke. Dokumentasjonen av Apples Core Data synes jeg er svært akademisk, og de fem bøkene jeg har om dette er dårlige.

Hintene som hjalp meg fant jeg på Stack Overflow etter å ha søkt etter @sum in core data på Google.

Sammen med Apples dokumentasjon klarte jeg tilslutt å løse problemet innenfor rammene av det nye verktøyet. Etter en ukes slit, ser løsningen latterlig enkel ut. Her er den:

• Predicate: bare bruk løsningen i STV! Pass bare på å lage predikatet slik:

  filterPredicate:[NSPredicate predicateWithFormat:@“account like ‘kreditt’”]];

• summering er så uskyldig som dette:

  NSNumber *balance = [transactionSection.items valueForKeyPath: @“@sum.amount”];

  self.title = balance.stringValue;

Dette er vidunderlig! Jeg kan bruke predikater i STV til å lage små og pene datasets, og beregne summen på datasettet i ettertid. Plutselig er det igjen morsomt å være database-programmerer!

The new unfinished user guide, provided as a PDF, is a good place to start. I followed Section 3 to set up the project.

I did made some errors; for instance I didn’t choose the Universal option when creating the project. And worse, I copied some invisible strange characters from the PDF into the source, and it ruined all.

But after a couple of days, and an hour a day, an empty project according to Section 3. was running.

Doing the first tests in Section 4. was also easy. So I decided to jump to Exploring Core Data Binding, which is what really interested me.

I did what the user guide told me, and again got an empty app. The guide didn’t mention to change the AppDelegate files, and after studying these I had a path to follow.

Since the PDF is not half completed, I looked at the samples provided. I got some ideas in the upgraded 2.0 samples, but these samples was written for earlier XCode versions.

What helped me, was the new ParseCom App. It was written in a new XCode version. So I used it’s AppDelegate files to rewrite my own project. And after some bug-fixing, it finally ran. And ran very nice indeed!

I make a receipt for you want to try it out here:

1. Setup your project as explained in Section 3. in the PDF provided
2. Do as told in the Section 4. “Exploring Core Data Binding”. Remember to check for Core Data.
3. Change the AppDelegate.h to the following:

#import <UIKit/UIKit.h>

//Added line
@class ViewController;

@interface AppDelegate : UIResponder`

@property (strong, nonatomic) UIWindow *window;

//Added line
@property (strong, nonatomic) ViewController *viewController;

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;

- (void)saveContext;
- (NSURL *)applicationDocumentsDirectory;

@end>

1. And the top of the AppDelegate.m as follows:

#import "AppDelegate.h"
#import "ViewController.h"
#import "iPadDetailViewController.h"

@implementation AppDelegate

@synthesize window = _window;

@synthesize viewController = _viewController;

@synthesize managedObjectContext = __managedObjectContext;
@synthesize managedObjectModel = __managedObjectModel;
@synthesize persistentStoreCoordinator = __persistentStoreCoordinator;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
self.viewController = [[ViewController alloc] initWithStyle:UITableViewStyleGrouped];
UIViewController *rootViewController;
rootViewController = [[UINavigationController alloc]initWithRootViewController:self.viewController];`

self.window.rootViewController = rootViewController;

[self.window makeKeyAndVisible];
return YES;
}

Run it on the iPhone simulator and you should have a great template to do ERP database programming on our lovely Apple mobile devices!

iPhone iOS 5 programming essentials ch. 39 are using a code first approach. That means defining outlets and actions in code, create the screen objects, and connect them manually.

I however, strongly prefer the UI first way explained by Paul Hegarty in his last Stanford course on iOS programming in the lectures 13 and 14.

Here it is his recommendations:

• Start with drawing the interface
• Create a new view controller, clean it, and connect it to the scene
• Generate code by dragging from the design to the .h file
• Import Paul’s core data controller from the course

Add the following to the view controller:

• setupFetchedResultController – setup table and field
• fetchDataIntoDocument – create initial data
• useData – if empty call fetchDataIntoDocument, if it does not exists call setupFRC
• setDatabase – call useData
• viewWillAppear – setup database from Document

Modify this method:

• cellForRowAtIndexPath – create each individual cell