barcode maker vb.net 6: Core Data and Hard-Core Design in Objective-C

Making Quick Response Code in Objective-C 6: Core Data and Hard-Core Design

CHAPTER 6: Core Data and Hard-Core Design
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you and fill in some details. But you can see, from Figure 6-1, that the tutorial has given you a start.
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Figure 6-1. The Locations project, before customization, with default table view and navigation controller behaviors
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But this does not do very much. You can add a data record and delete records, but you cannot edit anything. You cannot drill down into any object. But it does store data. (Yawn....) Let s go get some coffee, shall we (Queue intermission music.) All right, we re back! One obvious way to extend the app is to let the user drill down into a particular object instance. You could have a new type of view for this, or you could just use another UITableViewController subclass. Of course, this will need an array, not just one object. But I am going to treat the object as an array of attributes. I am going to use KVC to examine the object. This will work with any NSManagedObject subclass and not just this particular object.
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A View to an Object, Any Object
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You can make this controller more useful by making it more general. Right now, it is displaying the event object in a very specific way. You may also notice that the smarts about the way the event is being displayed is in the RootViewController class. However, turning the numbers and dates in the object into displayable strings is not really a job for the view. It would be more in keeping with the principles of the MVC design if the Event class itself knew how to display an event. You can thus simplify the tableView:(UITableView *)tableView cellForRowAtIndexPath: method by pushing that logic to the Event class. Now the RootViewController method will look like this:
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CHAPTER 6: Core Data and Hard-Core Design
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- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; // Dequeue or create a new cell UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease]; cell.textLabel.text = [[eventsArray objectAtIndex:indexPath.row] description]; cell.detailTextLabel.text = [[eventsArray objectAtIndex:indexPath.row] subdescription]; return cell; }
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The Event class now contains the following:
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#import "Event.h" @implementation Event @dynamic longitude; @dynamic latitude; @dynamic creationDate; - (NSString *)description { static NSDateFormatter *dateFormatter = nil; if (dateFormatter == nil) { dateFormatter = [[NSDateFormatter alloc] init]; [dateFormatter setTimeStyle:NSDateFormatterMediumStyle]; [dateFormatter setDateStyle:NSDateFormatterMediumStyle]; } return [dateFormatter stringFromDate:[self creationDate]]; } - (NSString *)subdescription { static NSNumberFormatter *numberFormatter = nil; if (numberFormatter == nil) { numberFormatter = [[NSNumberFormatter alloc] init]; [numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle]; [numberFormatter setMaximumFractionDigits:3]; } return [NSString stringWithFormat:@"%@, %@", numberFormatter stringFromNumber:self.latitude], numberFormatter stringFromNumber:self.longitude]]; } @end
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CHAPTER 6: Core Data and Hard-Core Design
The table given in the Locations tutorial does not respond when you click a row, but you want something to happen. The UINavigationController gives you an easy way to manage different kinds of views that are related to a hierarchy of objects. It allows you to maintain a stack of view controllers. When your UI is constrained, as it is on an iPhone, you need to make views that are simple, are obvious, and do just what you need them to do. Since a view can do only so much, you need a lot of views, and it turns out that managing the views on a stack is amazingly useful. If you respond to a click in a table row by creating another UIViewController subclass, you can push the new view controller onto the stack. The UINavigationController will take care of setting up a back button in the navigation bar. When the user clicks this button, the new view controller will be automatically popped, and you will be back to the top level of your object tree.
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { [tableView deselectRowAtIndexPath:indexPath animated:NO]; EventViewController * eventController = [[EventViewController alloc] init]; [eventController setEvent:[eventsArray objectAtIndex:indexPath.row]]; [[LocationsAppDelegate delegate].navigationController pushViewController:eventController animated:YES]; [eventController release]; }
You can create the EventViewController class now. It needs to be a subclass of UIViewController. It is useful to test the behavior at this point, before you add anything to your new class. If you test your application at this point, you will see the list of objects on the left when you launch (or a similar list), and then you will see the blank view on the right when you click a row. But you can verify that you can pop into this view and then hit the Locations button in the navigation bar, and you will pop back to the list of objects. As you can see in Figure 6-2, you can click any of the rows and come back out of the view and then click another object and do it again.
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