View Controllers CPRE 388

Transcription

1 View Controllers CPRE 388

2 View Controllers Manage views in model view controller design template. Many types: custom view controller; container view controller; modal view controller.

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4 Custom View controllers At least one per app. Subclass of UIViewController UIViewController instances have data (member vars), view through member vars pointing to IBOutlets, action methods, and any other view control related activities.

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6 Table View Controllers Table of data Selection management Row editing Table configuration Table view object managed by UITableViewController

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8 Navigation View Controller Container view controller to manage data/views organized hierarchically. Instance of class UINavigationController Manages multiple view controllers but also some views a navigation bar current location in data hierarchy; back button; custom controls for the current view

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10 Tab Bar Controller Container controller UITabBarController class Present same data differently or present different types of data If there are more views than the space for tabs on the tab bar, Tab bar controller also manages tab bar

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12 Modal View Controllers Just a mode of presenting a VC from another VC Generalization of container VCs. Typical present a view to gather some user information picking a picture for a calendar contact

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14 Anatomy: Custom View Controller

15 Custom VC essential tasks You must configure the view to be loaded by your view controller You must decide which orientations your view controller supports You must clean up the memory that is managed by your view controller

16 Typical VC Members Member variables pointing to the objects containing the data to be displayed by the corresponding views Member variables (or outlets) pointing to key view objects with which your view controller must interact Action methods that perform tasks associated with buttons and other controls in the view hierarchy Custom tasks

17 View Management Cycles Load cycle Unload cycle

18 Load Cycle Some part of your application asks for the view in the view controller s view property If the view is not currently in memory, the view controller calls its loadview method The loadview method responsible for loading a non nil view

19 loadview If over ridden, you are responsible for creating all views, and assigning a non nil view property. Default implementation uses nibname and nibbundle. If no nib file found, creates empty UIView object and assigns it to view property.

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22 Creating a VC (void)displaymodalview { MyViewController* vc = [[[MyViewController alloc] initwithnibname:@"myviewcontroller" bundle:nil] autorelease]; [self presentmodalviewcontroller:vc animated:yes]; }

23 Class MyViewController : UIViewController { id mybutton; id mytextfield; (nonatomic) IBOutlet id (nonatomic) IBOutlet id mytextfield; (IBAction)myAction:(id)sender;

24 Contents of MyViewConroller.nib

25 (void)loadview { self.wantsfullscreenlayout = YES; MetronomeView *view = [[MetronomeView alloc] initwithframe:[uiscreen mainscreen].applicationframe]; view.metronomeviewcontroller = self; self.view = view; self. [view release]; }

26 When overriding the loadview method to create your views programmatically, you should not call super. Doing so initiates the default view loading behavior and is usually just a waste of CPU cycles. Your own implementation of the loadview method should do all the work that is needed to create a root view and subviews for your view controller.

27 Cleaning up after Unloading Clean up references to view objects in: The dealloc method The viewdidunload method

28 View Orientations At minimum, portrait orientation needs to be supported by default. Additional orientations can be supported by a view controller (optionally). Both views and view controllers have to do additional work.

29 Orientations Override your view controller s shouldautorotatetointerfaceorientation: method Configure the autoresizing mask for each view in your view controller s view hierarchy

30 Orientation When the device orientation changes, systems sends out UIDeviceOrientationDidChangeNotification notification UIKit framework intercepts this notification and uses it to update your interface orientation automatically The window object does much of the work associated with changing the current orientation

31 Orientation Polls view controllers at the front to see if they support the alternate orientation. These view controllers should ask their subviews (controllers) about their support for the new (proposed) orientation.

32 Declaring the Supported Interface Orientations (BOOL)shouldAutorotateToInterfaceOrientation:( UIInterfaceOrientation)orientation { if ((orientation == UIInterfaceOrientationPortrait) (orientation == UIInterfaceOrientationLandscapeLeft)) return YES; return NO; }

33 View Resizing on Re Orientation the bounds of the affected views are modified automatically according to their autoresizing mask. you might use these notifications to make the following types of changes: Show or hide views that are specific to a particular orientation Show or hide views that are specific to a particular orientation Show or hide views that are specific to a particular orientation

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35 Memory Management critical data structures required by your view controller; Initialization methods; Creating view objects; loadview Allocating or loading data to be displayed in your view; viewdidload

36 Releasing refs to view objects; viewdidunload; Releasing the data not needed when view is not displayed; viewdidunload; Responding to low memory notifications; didreceivememorywarning Releasing critical data structures required by your view controller; dealloc