Messaging - Revision history

Mm: /* Delegation & Notification */

2010-05-07T17:47:36Z

Delegation & Notification

← Older revision		Revision as of 17:47, 7 May 2010
Line 41:		Line 41:

	Whereas notifications are usually broadcasted into the wide open space (not necessarily restricted to the app itself!) for interested listeners. It's pretty unsure if anyone is receiving this. Also, the message is handled by the notification center. Think about it like a news mailing by post or an electronic mailing list, where you don't know who's reading it and when it's received. In fact, chances are high, most objects will be notified the next run loop.		Whereas notifications are usually broadcasted into the wide open space (not necessarily restricted to the app itself!) for interested listeners. It's pretty unsure if anyone is receiving this. Also, the message is handled by the notification center. Think about it like a news mailing by post or an electronic mailing list, where you don't know who's reading it and when it's received. In fact, chances are high, most objects will be notified the next run loop.
	[[Image:Messaging.png\|420px]]		[[Image:Messaging.png\|420px\|left]]
			<br clear="all"/>

	You will find delegates all over the place. Important Delegate protocols are (just to name a few):		You will find delegates all over the place. Important Delegate protocols are (just to name a few):

Mm: /* Subclassing */

2010-03-07T12:07:19Z

Subclassing

← Older revision		Revision as of 12:07, 7 March 2010
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	== Subclassing ==		== Subclassing ==
	Sometimes there are simpler ways to get notified of certain events. For example, there are some methods in ~~UIView~~		Sometimes there are simpler ways to get notified of or to react to certain events. For example, there are some methods in UIViewController that can be overridden by subclasses:

	~~...~~


			<source lang="objc">
			- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation;
			- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration;
			- (void)willAnimateRotationToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation duration:(NSTimeInterval)duration;
			- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation;
			</source>

	== Delegation & Notification ==		== Delegation & Notification ==

Mm at 11:45, 7 March 2010

2010-03-07T11:45:36Z

← Older revision		Revision as of 11:45, 7 March 2010
Line 1:		Line 1:
			== Calling a Method ==
			There are quite different ways to call a method:

			Call selector for known class:
			* [object doSomething:TRUE];
			* NSString *s = [object name];
			Call selector for unknown class (type <id>*)
			* [object performSelector:@selector(doSomething:) withObject:[NSNuber numberWithBool:YES]];
			* [object performSelectorOnMainThread:@selector(doSomethingElse) withObject:nil waitUntilDone:NO];

			Use [[KVC]] (Key-Value-Coding) for Properties
			* NSString *s = [object valueForKey:@"name"];
			* [object setValue:@"Hello" forKey:@"name"];
			Use dot syntax (though this also works with action methods, it's recommended to use only for properties
			* NSString *s = object.name;
			* object.name = @"Hello";

			Note that in case of KVC- or performSelector:-messaging style, you have to use objects as parameters. They won't work with primitives (such as int, BOOL...). Note, that it's not possible to overload methods in ObjC, so you have to implement both methods. Usually this is done like this, eg:
			<source lang="objc">
			-(void)doSomething:(BOOL)value {
			//...
			}
			-(void)doSomething:(id)value {
			[self doSomething:[value boolValue]];
			}
			</source>


			== Subclassing ==
			Sometimes there are simpler ways to get notified of certain events. For example, there are some methods in UIView

			...



			== Delegation & Notification ==
			The main difference between Delegation and Notification is, that an object usually has only one delegate. The delegate can be informed to react on changes; or it can be asked for opinion or help. Think about it like a red telephone where you can rely on getting your manager on the phone immediately to discuss important matters.

			Whereas notifications are usually broadcasted into the wide open space (not necessarily restricted to the app itself!) for interested listeners. It's pretty unsure if anyone is receiving this. Also, the message is handled by the notification center. Think about it like a news mailing by post or an electronic mailing list, where you don't know who's reading it and when it's received. In fact, chances are high, most objects will be notified the next run loop.
	[[Image:Messaging.png\|420px]]		[[Image:Messaging.png\|420px]]

			You will find delegates all over the place. Important Delegate protocols are (just to name a few):
			* UIApplicationDelegate
			* UITableViewDelegate
			* UITextViewDelegate
			* UIAccelerometerDelegate
			* MKMapViewDelegate
			* CGLocationManagerDelegate
			* ...

			== Delegates ==

			Delegation is a very important design pattern with cocoa. Usually it's much simpler or cleaner to use a delegate instead of subclassing. The one delegate we are using all the time is UIApplication delegate. Classes providing delegate functions have a protocol with defines required and optional methods to be implemented by the object's delegate:

			<source lang="objc">
			// if a class follows a delegate protocol, we add this to the header
			// the only reason for this is to ensure we implement all the required methods, eg:
			@interface MyAppDelegate : NSObject <UIApplicationDelegate> { }
			// Next, you have to either set the delegate in Interface Builder or do so programmatically
			[[UIApplication sharedApplication] setDelegate:self];
			// Then you can implement following <UIApplicationDelegate> method to get informed once the app has finished launching
			–(void)applicationDidFinishLaunching:(UIApplication*)application;
			</source>


			== Notifications ==

			Notifications get broadcasted to all and everything that registered as observer to a certain notification:

			<source lang="objc">
			// +++ The Observer +++
			// usually on -init or -awakeFromNib:
			[[NSNotificationCenter defaultCenter] addObserver:self
			selector:@selector(receiveNotification:)
			name:@"SomethingHappenedNotification"
			object:nil];
			// then implement your custom method ( -(void)receiveNotification:(NSNotification*)notification; )
			// and finally remove notification observers before deallocation
			[[NSNotificationCenter defaultCenter] removeObserver:self];

			// +++ The Broadcaster +++
			// broadcast a notification to all registered objects
			[[NSNotificationCenter defaultCenter] postNotificationName:@"SomethingHappenedNotification"
			object:self];
			</source>

			== Ressources ==
			* [http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/CocoaFundamentals/CommunicatingWithObjects/CommunicateWithObjects.html#//apple_ref/doc/uid/TP40002974-CH7-SW15 Cocoa Fundamentals Guide: Communicating With Objects] - recommended reading!


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Mm: Created page with '420px {{Template:iPhoneDev}}'

2010-03-07T02:39:37Z

Created page with '420px {{Template:iPhoneDev}}'

New page

[[Image:Messaging.png|420px]]

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