iOS Development (Part 2)

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Use of TextField, Label, Sliders and Switch buttons …

Use of TextField, Label, Sliders and Switch buttons
Handling ActionSheet and Alerts
Application Delegates
Handling ActionSheet and Alerts
Application Delegates
UIApplication Delegates
View Controllers
Life Cycle of Application & Methods
ARC
iPhone App Development Training Programme (contd.)

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  • It is an important feature of any object-oriented programming environment and the iPhone SDK is no exception to this rule. Subclassing allows us to create a new class by deriving from an existing class and then extending the functionality. In so doing we get all the functionality of the parent class combined with the ability to extend the new class with additional methods and properties.Subclassing is typically used where an existing class exists that does most, but not all, of what you need. By subclassing we get all that existing functionality without having to duplicate it and simply add on the functionality that was missing.We will see an example of subclassing in the context of iPhone development when we start to work with view controllers. The UIKit framework contains a class called the UIViewController. This is a generic view controller from which we will create a subclass so that we can add our own methods and properties.
  • The next argument is the delegate for the action sheet. The action sheet’s delegate will be notified when a button on that sheet has been tapped. More specifically, the delegate’s actionSheet:didDismissWithButtonIndex: method will be called. By passing self as the delegate parameter, we ensure that our version of actionSheet:didDismissWithButtonIndex: will be called. Why didn’t we just use view, instead of self.view? view is a private instance variable of our parent class UIViewController, which means we can’t access it directly, but instead must use an accessor method.
  • @class doesn't import the file, it just says to the compiler "This class exists even though you don't know about it, don't warn me if I use it". #import actually imports the file so you can use all the methods and instance variables. @class is used to save time compiling (importing the whole file makes the compile take more time). You can use #import if you want, it will just take longer for your project to build.

Transcript

  • 1. iOS Development (Part II) COMPILED BY: ASIM RAIS SIDDIQUI
  • 2. Goals of the Lecture  Use of TextField, Label, Sliders and Switch buttons  Handling ActionSheet and Alerts  Application Delegates  Handling ActionSheet and Alerts  Application Delegates  UIApplication Delegates  View Controllers  Life Cycle of Application & Methods  ARC
  • 3. Application Delegate  A delegate is an object that acts on behalf of, or in coordination with, another object when that object encounters an event in a program. The delegating object is often a responder object—that is, an object inheriting from NSResponder in AppKit or UIResponder in UIKit—that is responding to a user event. The delegate is an object that is delegated control of the user interface for that event, or is at least asked to interpret the event in an application-specific manner.  These objects are designed to fulfill a specific role in a generic fashion; a window object in the AppKit framework, for example, responds to mouse manipulations of its controls and handles such things as closing, resizing, and moving the physical window.
  • 4. UIApplication & Delegates
  • 5. View Controllers View controllers are a vital link between an app’s data and its visual appearance. Whenever an iOS app displays a user interface, the displayed content is managed by a view controller or a group of view controllers coordinating with each other. Therefore, view controllers provide the skeletal framework on which you build your apps. iOS provides many built-in view controller classes to support standard user interface pieces, such as navigation and tab bars. As part of developing an app, you also implement one or more custom controllers to display the content specific to your app.
  • 6. Life Cycle & Methods
  • 7. Note:  When Apple switched the default compiler from GCC to LLVM recently, it stopped being necessary to declare instance variables for properties. If LLVM finds a property without a matching instance variable, it will create one automatically.
  • 8. ARC  Automatic Reference Counting (ARC) is a new feature of the Objective-C language, introduced with iOS 5, that makes your life much easier.  It’s no longer necessary to release objects. Well, that’s not entirely true. It is necessary, but the LLVM 3.0 compiler that Apple started shipping with iOS 5 is so smart that it will release objects for us, using a new feature called Automatic Reference Counting, or ARC, to do the heavy lifting. That means no more dealloc methods, and no more worrying about calling release or autorelease.  ARC is very cool, but it’s not magic. You should still understand the basic rules of memory management in Objective-C to avoid getting in trouble with ARC. To brush up on the Objective-C memory management contract, read Apple’s Memory Management Programming Guide at this URL:  https://developer.apple.com/library/ios/#documentation/Cocoa/Con cep tual/MemoryMgmt/
  • 9. Subclassing  It is an important feature of any object-oriented programming environment and the iPhone SDK is no exception to this rule. Subclassing allows us to create a new class by deriving from an existing class and then extending the functionality. In so doing we get all the functionality of the parent class combined with the ability to extend the new class with additional methods and properties.
  • 10. Subclassing @interface Superclass : NSObject { int v; } - (void)initV; @end @implementation Superclass - (void)initV { v = 20; } @end @interface Subclass : Superclass { int w; } - (void)displayVars; @end @implementation Subclass - (void)initW { w = 50; } - (void)displayVars { NSLog(@"v is %d, w is %d", v, w); } @end
  • 11. Subclassing int main(int argc, char *argv[]) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; Subclass *sub = [[Subclass alloc] init]; [sub initV]; // Inherited method & ivar [sub initW]; // Own method & ivar [sub displayVars];// Inherited method [sub release]; [pool drain]; return 0; } Output: v is 20, w is 50
  • 12. Action Sheet and Alert  Action sheets are used to force the user to make a choice between two or more items. The action sheet comes up from the bottom of the screen and displays a series of buttons. Users are unable to continue using the application until they have tapped one of the buttons. Action sheets are often used to confirm a potentially dangerous or irreversible action such as deleting an object.  Alerts appear as a blue, rounded rectangle in the middle of the screen. Just like action sheets, alerts force users to respond before they are allowed to continue using the application. Alerts are usually used to inform the user that something important or out of the ordinary has occurred. Unlike action sheets, alerts may be presented with only a single button, although you have the option of presenting multiple buttons if more than one response is appropriate.
  • 13. Conforming to the Action Sheet Delegate Method  In order for our controller class to act as the delegate for an action sheet, it needs to conform to a protocol called UIActionSheetDelegate.  @interface BIDViewController : UIViewController <UIActionSheetDelegate>  Other parameter allow you to add more buttons  E.g otherButtonTitles:@"Foo", @"Bar", nil
  • 14. Switching Views  presentModalViewController and presentViewController  Other different techniques to switch views  - view overlapping  - navigation controller
  • 15. Navigation Controller  The main tool you’ll use to build hierarchical applications is UINavigationController. UINavigationController is similar to UITabBarController in that it manages, and swaps in and out, multiple content views. The main difference between the two is that UINavigationController is implemented as a stack, which makes it well suited to working with hierarchies.  A stack is a commonly used data structure that works on the principle of last in, first out.
  • 16. Stack  A computer stack follows the same rules:  When you add an object to a stack, it’s called a push. You push an object onto the stack.  The first object you push onto the stack is called the base of the stack.  The last object you pushed onto the stack is called the top of the stack  (at least until it is replaced by the next object you push onto the stack).  When you remove an object from the stack, it’s called a pop. When you pop an object off the stack, it’s always the last one you pushed onto the stack. Conversely, the first object you push onto the stack will always be the last one you pop off the stack.
  • 17. Setting Up the Navigation Controller  Add property in main app delegate file @property (strong, nonatomic) UINavigationController *navController; Then implement self.navController = [[UINavigationController alloc] initWithRootViewController:self.viewController]; User push or pop, when needed: [self.navigationController pushViewController:foo animated:YES];
  • 18. TableViews  First, what’s a Table View in iPhone app? Table View is one of the common UI elements in iOS apps. Most apps, in some ways, make use of Table View to display list of data.  The best example is the built-in Phone app. Your contacts are displayed in a Table View.  Another example is the Mail app. It uses Table View to display your mail boxes and emails. Not only designed for showing textual data, Table View allows you to present the data in the form of images. The built-in Video and YouTube app are great examples for the usage.
  • 19. UITableViewDelegate and UITableViewDataSource  The UITableView, the actual class behind the Table View, is designed to be flexible to handle various types of data. You may display a list of countries or contact names. Or like this example, we’ll use the table view to present a list of recipes. So how do you tell UITableView the list of data to display? UITableViewDataSource is the answer. It’s the link between your data and the table view. The UITableViewDataSource protocol declares two required methods (tableView:cellForRowAtIndexPath and tableView:numberOfRowsInSection) that you have to implement. Through implementing these methods, you tell Table View how many rows to display and the data in each row.  UITableViewDelegate, on the other hand, deals with the appearance of the UITableView. Optional methods of the protocols let you manage the height of a table row, configure section headings and footers, re-order table cells, etc. We do not change any of these methods in this example. Let’s leave them for the next tutorial.
  • 20.  numberOfSectionsInTableView  numberOfRowsInSection  cellForRowAtIndexPath  didSelectRowAtIndexPath
  • 21. Tab Bar App  No more windows.xib file  Add ThirdViewController subclassing UIViewController  Add DetailViewController subclassing UIViewController  #import "ThirdViewController.h"  Create new class object  ThirdViewController *navController = [[ThirdViewController alloc] initWithNibName:@"ThirdViewController" bundle:nil];  Create Navigation instance  UINavigationController *nav=[[UINavigationController alloc] initWithRootViewController:navController];
  • 22. @class Directive  The @class directive sets up a forward reference to another class. It tells the compiler that the named class exists, so when the compiler gets to, say an @property directive line, no additional information is needed, it assumes all is well and plows ahead.
  • 23. @Classs Vs #Import