16  Incorporating a Tab Bar into Your Application

@property (nonatomic, retain) IBOutlet UIWindow *window;

@property (nonatomic, retain) UITabBarController *tabBarController;

@end



Here is the implementation (.m) file of the application delegate with a tab bar:

#import "ViewsAndVCAppDelegate.h"

#import "FirstViewController.h"

#import "SecondViewController.h"

@implementation ViewsAndVCAppDelegate

@synthesize window;

@synthesize tabBarController;

- (BOOL)

application:(UIApplication *)application

didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

/* Create the first View Controller */

FirstViewController *firstController =

[[FirstViewController alloc]

initWithNibName:@"FirstViewController"

bundle:nil];

/* Now create the second View Controller */

SecondViewController *secondController =

[[SecondViewController alloc]

initWithNibName:@"SecondViewController"

bundle:nil];

/* Stack up all the View Controllers into an array */

NSArray *arrayofViewControllers = [NSArray arrayWithObjects:

firstController,

secondController,

nil];

[firstController release];

[secondController release];

/* Instantiate your Tab Bar Controller */

UITabBarController *theTabBarController =

[[UITabBarController alloc] init];

self.tabBarController = theTabBarController;

[theTabBarController release];

/* Set the array of View Controllers of the Tab Bar Controller */

[self.tabBarController setViewControllers:arrayofViewControllers

animated:YES];

/* Show the View of the Tab Bar Controller */

[window addSubview:self.tabBarController.view];

[window makeKeyAndVisible];



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return YES;

}

- (void)dealloc {

[tabBarController release];

[window release];

[super dealloc];

}

@end



Discussion

A tab bar is a special control that appears at the bottom of the screen of an iOS application (see Figure 2-18 for an example). Using a tab bar, you can present different types

of data to the users of your application in separate sections. These sections are called

tab bar items. The Clock and Phone applications included in iOS provide examples of

tab bars (the Phone application is exclusive to the iPhone).

We can create tab bars by instantiating an object of type UITabBarController and adding

it to the main window of our application, as shown in the code in this recipe’s Solution.



Figure 2-18. A simple tab bar at the bottom of the screen displaying two tab bar items (labeled “First”

and “Second,” from left to right)



Instances of the UITabBarController retain a property called viewControllers of type

NSArray. This property is the list of all the instances of UIViewController that the tab

bar must display on the screen. Please bear in mind that UINavigationController is also

a subclass of UIViewController, and therefore can be added to this array. By setting this

property to an array, the new set of view controllers will get displayed in the tab bar (if

the tab bar itself has already been added to the current window), without an animation.

However, to enable the animation, you must call the setViewControllers:animated:

instance method of UITabBarController.

UIViewController instances are able to change their tab bar item’s behavior by accessing

a property named tabBarItem. View controllers can then change the image (for instance)



that gets displayed on their corresponding tab bar item by assigning an instance of

UIImage to the image property of tabBarItem:

- (void)viewDidLoad {

[super viewDidLoad];



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}



UIImage *tabImage = [UIImage imageNamed:@"FirstTabImage.png"];

self.tabBarItem.image = tabImage;



- (void) viewDidUnload{

[super viewDidUnload];

}



self.tabBarItem.image = nil;



2.17 Pop Up Additional Information over iPad UI Elements

Problem

You want to display data to iPad users, without blocking the main screen’s contents.



Solution

Use popovers on the iPad:

#import "ViewsAndVCAppDelegate.h"

#import "LeftViewController.h"

#import "RightViewController.h"

@implementation ViewsAndVCAppDelegate

@synthesize

@synthesize

@synthesize

@synthesize



window;

splitViewController;

rightViewController;

leftViewController;



- (void)splitViewController:(UISplitViewController*)svc

willHideViewController:(UIViewController *)aViewController

withBarButtonItem:(UIBarButtonItem*)barButtonItem

forPopoverController:(UIPopoverController*)pc{

barButtonItem.title = NSLocalizedString(@"Left Item", nil);

[self.rightViewController.navigationItem

setLeftBarButtonItem:barButtonItem

animated:YES];

}

Rest of application delegate's implementation...



Discussion

iOS applications running on the iPad can take advantage of popovers. An example is

the New Element popover shown in Figure 2-19.

Popovers are an efficient way to display data temporarily to the user. They are commonly used in iPad applications that use split view controllers that support both

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Figure 2-19. The New Element popover, which is displayed when the user selects the + button



landscape and portrait orientations. For more information about split view controllers,

please refer to Recipe 2.6.

In portrait mode, a split view controller hides its left (master) view controller to give

all the space on the screen to the right (detail) view controller. However, because users

still need access to the hidden master controller, all it takes is a press of a button on the

right view controller to display the contents of the left view controller in a popover.

Popovers are different from modal view controllers because popovers use limited space

on the main window and still allow interactivity with the screens beneath them; a modal

view controller prevents interaction with other screens while the modal view controller

is still displaying.

Popovers are created using the UIPopoverViewController. Popovers can be managed

and displayed in two ways:

• Use a split view controller and listen to its delegate messages that can automatically

create popovers for you.

• Manually create instances of UIPopoverViewController and present them to the user

using various instance methods available in the aforementioned class.

Let’s look at the first method. In this example, we will build on the same example code

in Recipe 2.6. Here is what we want to accomplish:

• If the user opens the application in landscape mode:

— The user will see one view controller on the left (master) side and another view

controller on the right (detail) side.

— When the user picks an item on the left (master) side, the same item gets displayed as the title of the right (detail) side.

• Now if the user rotates the device to portrait mode:

— We want to display a button on the top left of the navigation bar of the right

(detail) side.

— Once the user taps on that button, we want the contents of the left (master) side

to get displayed in a popover on the right (detail) side.

So, how do we go about doing this? Simple! We do this one step at a time:



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