vb.net print barcode labels Object model and object context getter methods in Objective-C

Encoder QR Code JIS X 0510 in Objective-C Object model and object context getter methods

Listing 9.10 Object model and object context getter methods
Encoding QR In Objective-C
Using Barcode generation for iPhone Control to generate, create QR Code image in iPhone applications.
www.OnBarcode.com
EAN / UCC - 13 Creation In Objective-C
Using Barcode creation for iPhone Control to generate, create EAN13 image in iPhone applications.
www.OnBarcode.com
- (NSManagedObjectContext *) managedObjectContext { if (managedObjectContext != nil) { return managedObjectContext; }
Printing UCC - 12 In Objective-C
Using Barcode creation for iPhone Control to generate, create EAN 128 image in iPhone applications.
www.OnBarcode.com
Painting Code-39 In Objective-C
Using Barcode maker for iPhone Control to generate, create Code 3 of 9 image in iPhone applications.
www.OnBarcode.com
Download from Wow! eBook <www.wowebook.com>
UPC-A Supplement 5 Creator In Objective-C
Using Barcode creator for iPhone Control to generate, create GTIN - 12 image in iPhone applications.
www.OnBarcode.com
Denso QR Bar Code Maker In Objective-C
Using Barcode drawer for iPhone Control to generate, create Denso QR Bar Code image in iPhone applications.
www.OnBarcode.com
Data: advanced techniques
Barcode Encoder In Objective-C
Using Barcode creator for iPhone Control to generate, create Barcode image in iPhone applications.
www.OnBarcode.com
Making GS1 - 8 In Objective-C
Using Barcode encoder for iPhone Control to generate, create EAN / UCC - 8 image in iPhone applications.
www.OnBarcode.com
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator]; if (coordinator != nil) { managedObjectContext = [[NSManagedObjectContext alloc] init]; [managedObjectContext setPersistentStoreCoordinator: coordinator]; } return managedObjectContext; } - (NSManagedObjectModel *)managedObjectModel { if (managedObjectModel != nil) { return managedObjectModel; } managedObjectModel = [[NSManagedObjectModel mergedModelFromBundles:nil] retain]; return managedObjectModel; }
QR Code 2d Barcode Maker In Visual C#
Using Barcode maker for .NET Control to generate, create QR Code image in .NET applications.
www.OnBarcode.com
QR Maker In Java
Using Barcode generation for BIRT Control to generate, create QR Code JIS X 0510 image in BIRT applications.
www.OnBarcode.com
Both of these methods check to see if their property has been initialized. If not, they re initialized and returned. The final method you need to implement is applicationWillTerminate. This is where you ll save your managed object context to the data store. You save your context every time the user makes a change to the data. This code is needed in case some unsaved data is lying around when the application exits. Listing 9.11 shows the code for this method.
Drawing Barcode In .NET
Using Barcode generator for Reporting Service Control to generate, create Barcode image in Reporting Service applications.
www.OnBarcode.com
Code 39 Full ASCII Printer In None
Using Barcode drawer for Microsoft Word Control to generate, create USS Code 39 image in Word applications.
www.OnBarcode.com
Listing 9.11 Saving the managed object context
PDF 417 Maker In None
Using Barcode generator for Software Control to generate, create PDF 417 image in Software applications.
www.OnBarcode.com
2D Barcode Encoder In .NET
Using Barcode creator for ASP.NET Control to generate, create Matrix 2D Barcode image in ASP.NET applications.
www.OnBarcode.com
- (void)applicationWillTerminate:(UIApplication *)application { NSError *error = nil; if (managedObjectContext != nil) { if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } } }
Code 39 Generation In None
Using Barcode generation for Font Control to generate, create Code39 image in Font applications.
www.OnBarcode.com
Generate USS-128 In None
Using Barcode generator for Office Excel Control to generate, create UCC - 12 image in Microsoft Excel applications.
www.OnBarcode.com
The first thing this method does is check to see if your managedObjectContext is nil. This will most likely never be the case, but it s still good practice to check. Next, you check to see if there are any unsaved changes to the context by calling the hasChanges method. The context will have changes anytime something is added, modified, or deleted. If changes are present, the context is saved by calling the save method. Similarly to the code in listing 9.9, you call the abort method in the event of an error in order to generate a crash log. You re now ready to make changes to your data.
Draw Code 128 Code Set B In Java
Using Barcode creation for BIRT reports Control to generate, create ANSI/AIM Code 128 image in BIRT applications.
www.OnBarcode.com
UPC Symbol Creation In VS .NET
Using Barcode encoder for Reporting Service Control to generate, create UPC-A Supplement 5 image in Reporting Service applications.
www.OnBarcode.com
Download from Wow! eBook <www.wowebook.com>
1D Printer In Visual Basic .NET
Using Barcode creation for .NET Control to generate, create Linear image in .NET applications.
www.OnBarcode.com
Recognize UPC-A Supplement 5 In .NET Framework
Using Barcode recognizer for .NET Control to read, scan read, scan image in VS .NET applications.
www.OnBarcode.com
An introduction to Core Data
Adding objects to the database
As you ve seen, to work with database objects in SQLite, you must write the raw SQL code. Also, every time you want to add a record, you must write many lines of code that can t be reused in other areas. This is where the true power of Core Data comes in. In Core Data, you re working with only the class files that were generated from your data model. This allows you to manipulate them as you would any other object in Objective-C. Let s start by looking at the code to add an object to the database. Listing 9.12 shows the code for adding a new entity to the database.
Listing 9.12 Adding an entity to the database
Entry * e = (Entry *)[NSEntityDescription insertNewObjectForEntityForName:@"Entry" inManagedObjectContext:managedObjectContext]; [e setTitle:textField.text]; [e setBody:textView.text]; [e setCreationDate:[NSDate date]]; NSError *error; if (![managedObjectContext save:&error]) { NSLog(@"Error Saving: %@",[error description]); }
As you can see, the only difference here is how you initialize the Entry object. Instead of doing a [[Entry alloc] init], you allow Core Data to create a new object inside the context. After this object has been created, you can begin using its accessor and mutator methods. You can even create your own methods inside these objects and call them. When you re ready to save your managed object, you call the save method of the managed object context. This causes your changes to be made permanent by writing them to the database.
Fetching, updating, and deleting objects in Core Data
To update or delete objects from the database, you must first have them in memory. To do this, you need to fetch them into an array. Fetching in Core Data is much more elegant than it is in SQL. You tell Core Data what objects you want and how to sort the objects, and it returns them in an array with little code. Listing 9.13 shows the code to do a simple fetch on your journal entries and sort them by their creation date.
Listing 9.13 Fetching data
NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription Creates sort entityForName:@"Entry" descriptor inManagedObjectContext:managedObjectContext]; to sort results [request setEntity:entity]; NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc]
Copyright © OnBarcode.com . All rights reserved.