Question

In my application i have some view controllers and one objective c class ,how can i access the UI elemets of one view controller to change their values in objective class .

To explain further , i have a UILable *lab in the firstviewcontroller and just imported

#import "firstViewController.h"

in my customclass.m file and i am trying to do like this in one method of objective c class

 firstViewController.lab.text=@"example"; 

( i know its not correct method but i am trying to explain what i am doing )

can any one please tell me how can i do that ?

Answer 1

First thing you need to do is grab a reference to the view controller you wish to operate on. One way to do this and have it available to other classes is to store a reference to it in a singleton object that you instantiate in your customclass.m. Specifically this is how this method works:

Define Singleton Object:

#import <Foundation/Foundation.h>

@interface MySingleton : NSObject {
     MyViewController *myViewController;

}
@propery (nonatomic. retain) MyViewController *myViewController;
+(MySingleton*)sharedMySingleton;

@implementation MySingleton
@synthesize myViewController;
static MySingleton* _sharedMySingleton = nil;

+(MySingleton*)sharedMySingleton
{
    @synchronized([MySingleton class])
    {
        if (!_sharedMySingleton)
            [[self alloc] init];

        return _sharedMySingleton;
    }

    return nil;
}

+(id)alloc
{
    @synchronized([MySingleton class])
    {
        NSAssert(_sharedMySingleton == nil, @"Attempted to allocate a second instance of a singleton.");
        _sharedMySingleton = [super alloc];
        return _sharedMySingleton;
    }

    return nil;
}

-(id)init {
    self = [super init];
    if (self != nil) {
        // initialize stuff here
    }

    return self;
}

@end

Whereever you instantiate your myViewController you do this:

#import "MySingleton.h"

MySingleton *sinlgeton = [MySingleton sharedMySingleton];
singleton.myViewController = myViewController;

Now in your CustomClass.m you do this:

#import "MySingleton.h"

    MySingleton *sinlgeton = [MySingleton sharedMySingleton];
    singleton.myViewController.lab.text = @"example"

As I said this is ONE WAY to do this. However, you most probably DO NOT want to access and change view controller properties in a custom class so you should really rethink why you are doing this at all.