Call Void on First View Controller from Second View Controller in Xcode

Question

I am using Xcode 4.6.2 and have created a new Tabbed Application using apples template. I have placed a UIWebView on my First View Controller and loaded http://google.co.uk into it. On my Second View Controller I have created a button that, when pressed, will load http://google.co.uk/images into the Web View on the first controller. It is this bit I am stuck on, here is my code so far:

FirstViewController.h

#import <UIKit/UIKit.h>  

@interface FirstViewController : UIViewController {  
    IBOutlet UIWebView *mainWebView;  
}  

-(void)imagesURL;  

@end

FirstViewController.m

#import "FirstViewController.h"

@interface FirstViewController ()

@end

@implementation FirstViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        self.title = NSLocalizedString(@"First", @"First");
        self.tabBarItem.image = [UIImage imageNamed:@"first"];
    }
    return self;
}

- (void)viewDidLoad
{
    [mainWebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.co.uk"]]];

    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)imagesURL {
    [mainWebView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://google.co.uk/images"]]];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

SecondViewController.h

#import <UIKit/UIKit.h>
#import "FirstViewController.h"

@interface SecondViewController : UIViewController {

}

- (IBAction)imagesButton:(id)sender;

@end

SecondViewController.m

#import "SecondViewController.h"
#import "FirstViewController.h"

@interface SecondViewController ()

@end

@implementation SecondViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        self.title = NSLocalizedString(@"Second", @"Second");
        self.tabBarItem.image = [UIImage imageNamed:@"second"];
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)imagesButton:(id)sender {
    FirstViewController *view1 = [[FirstViewController alloc] init];
    [view1 imagesURL];
}
@end

At the moment, when I press the Images button on the Second View Controller and switch back to the first, nothing happens at all. The webpage doesn't load. its like the Void isn't being called. What am I doing wrong?

Answer 1

The problem is in this line here FirstViewController *view1 = [[FirstViewController alloc] init]; - that is creating an entirely new copy of your view controller, which is not the one you started with in your first tab.

I think you would benefit from following some Objective C tutorials, or perhaps one of the iOS programming courses on iTunes U so that if something like this occurs again you have some more background.

There are many ways to do what you are trying to do, but one of the most straightforward is to have your second view controller talk to the tab view controller displaying it to get the first view controller. There should be reasonable documentation about how to do this in the iOS UITabViewController docs.