Load all Viewcontrollers when application opens - ios

Question

I'm working on a tabbed application for iOS. Because the tabbar icons are loaded in each viewcontroller separately, I was wondering if it is possible to load all the viewcontrollers at once in the background so all the tabbar icons are loaded when the application is launched.
The tabbar makes use of two icons for each tabbar item (selected and unselected), thats why I choose to load the icons in each viewcontroller separately
And otherwise, is there a possibility to load the tabbar icons in the App delegate?

Answer 1

Yes it is possible. You can initialize all controllers and all images in App delegate's didFinishLaunchingWithOptions methods. Here is the example:
UIViewController *locateTabController = [[LocationTabController alloc] initWithNibName:#"LocationTabController" bundle:nil];
UINavigationController *locationTabNavigationController = [[UINavigationController alloc] initWithRootViewController:locateTabController];
// Product Tab
UIViewController *productsTabController = [[ProductsTabController alloc] initWithNibName:#"ProductsTabController" bundle:nil];
UINavigationController *productsTabNavigationController = [[UINavigationController alloc] initWithRootViewController:productsTabController];
// Delivery Tab
UIViewController *nextDeliveryTabController = [[DeliveryTabController alloc] initWithNibName:#"DeliveryTabController" bundle:nil];
UINavigationController *nextDeliveryTabNavigationController = [[UINavigationController alloc] initWithRootViewController:nextDeliveryTabController];
// Order Tab
UIViewController *standingOrderTabController = [[OrderTabController alloc] initWithNibName:#"OrderTabController" bundle:nil];
UINavigationController *standingOrderTabNavigationController = [[UINavigationController alloc] initWithRootViewController:standingOrderTabController];
self.tabBarController = [[UITabBarController alloc] init];
self.tabBarController.viewControllers = [NSArray arrayWithObjects:locationTabNavigationController, productsTabNavigationController,nextDeliveryTabNavigationController, standingOrderTabNavigationController, nil];
Here navigation controller is provided as every tab controller class had its own navigation.
You can add titles and images at the same time.
/// Adding titles on each of the tab bar controllers
[[self.tabBarController.viewControllers objectAtIndex:0] setTitle:#"Locate"];
[[[self.tabBarController.viewControllers objectAtIndex:0] tabBarItem]setFinishedSelectedImage:[UIImage imageNamed:#"LocateIconActive.png"] withFinishedUnselectedImage:[UIImage imageNamed:#"LocateIconInactive.png"]];
[[self.tabBarController.viewControllers objectAtIndex:1] setTitle:#"Products"];
[[[self.tabBarController.viewControllers objectAtIndex:1] tabBarItem]setFinishedSelectedImage:[UIImage imageNamed:#"ProductsIconActive.png"] withFinishedUnselectedImage:[UIImage imageNamed:#"ProductsIconInactive.png"]];
[[self.tabBarController.viewControllers objectAtIndex:2] setTitle:#"Delivery"];
[[[self.tabBarController.viewControllers objectAtIndex:2] tabBarItem]setFinishedSelectedImage:[UIImage imageNamed:#"NextDeliveryIconActive.png"] withFinishedUnselectedImage:[UIImage imageNamed:#"NextDeliveryIconInactive.png"]];
[[self.tabBarController.viewControllers objectAtIndex:3] setTitle:#"Order"];
[[[self.tabBarController.viewControllers objectAtIndex:3] tabBarItem]setFinishedSelectedImage:[UIImage imageNamed:#"StandingOrderIconActive.png"] withFinishedUnselectedImage:[UIImage imageNamed:#"StandingOrderIconInactive.png"]];

Answer 2

Sub class your UITabBarController and set the images on the viewWillAppear. I found that this is the cleanest way of doing it.

Answer 3

You dont need to load any viewcontroller when application opens for this purpose. All you have to do is set tabbar icon inside each viewcontroller's initialization method like below:
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization
self.tabBarItem.image = [UIImage imageNamed:IMAGE_NAME];
[self.tabBarItem setFinishedSelectedImage:[UIImage imageNamed:IMAGE_NAME] withFinishedUnselectedImage:[UIImage imageNamed:IMAGE_NAME]];
self.tabBarItem.title = TITLE;
}
return self;
}
After that when you initialize the viewcontroller object from the AppDelegate, tabbar icon will be set.
viewController = [[ViewController alloc] initWithNibName:#"ViewController" bundle:nil];