Calling method from another class doesn't work properly - ios

Question

I am trying to change the text and the position of a UILabel from another class.
I have successfully managed to call my -changeLabel method, which is in my FirstViewController class, from my SecondViewController class. Here is the code I have used in my two classes:
SecondViewController:
#import "FirstViewController.h"
#interface SecondViewController ()
#property (nonatomic,strong) FirstViewController *firstViewController;
#end
#implementation SecondViewController
#synthesize firstViewController;
- (IBAction)button:(id)sender {
firstViewController = [[FirstViewController alloc] init];
[firstViewController changeLabel];
}
FirstViewController:
- (void)changeLabel {
NSLog(#"changeLabel is called!");
label.text = #"New text.";
label.frame = CGRectMake(10, 100, 150, 40);
NSLog(#"%#", label.text);
NSLog(#"%f", label.frame.size.width);
}
The weird thing is that the logger looks like this after pressing the "button" that calls the method:
"2013-12-30 19:24:50.303 MyApp[655:70b] changeLabel is called!"
"2013-12-30 19:24:50.305 MyApp[655:70b] New text."
"2013-12-30 19:24:50.308 MyApp[655:70b] 0.000000"
So it seems the label text change, but it doesn't show up on the screen. And the label width is logged as 0.0.. even though I just set it to 150.
Why is this happening? Am I not able to change frame variables from another class? Is there another way to do this?
IMPORTANT:
As the FirstViewController is the main view controller while the SecondViewController is a side menu, similar to the facebook app:
I want to be able to press a "button" on the SecondViewController(side menu) and call a method in the FirstViewController(main) that changes the position(frame) of a UILabel.
EDIT:
Here is how I created the UILabel:
label = [[UILabel alloc] init];
label.frame = CGRectMake(0, 0, 150, 40);
label.text = #"Text."
[self.view addSubview:label];

Answer 1

I think problem is this. You are calling method from new instance of FirstViewController.
Let assume
1. FirstViewController at stack[0].
2. SecondViewController at stack[1].
If you are navigating or moving from
FirstViewController->SecondViewController
In this case FirstViewController already in memory with some address 0x23ffff.
And in SecondViewController you are again creating new instance of FirstViewController which is point to another address '0x234jurhu`
- (IBAction)button:(id)sender {
firstViewController = [[FirstViewController alloc] init];
[firstViewController changeLabel];
}
Don't create new instance here.
You can use delegate or NSNotification concept for this.

Answer 2

How are you displaying FirstViewController?
Here is the issue:
firstViewController = [[FirstViewController alloc] init];
[firstViewController changeLabel];
You creating a new instance of FirstViewController and updating the label text. If your using these VC's in a navigation stack and you pop back to FirstViewController from SecondViewController, you won't see any label change because they are different instances of the class.
If your using FirstViewController as a childViewController of SecondViewController (with naming of them I don't think this what your doing), then in the - (IBAction)button:(id)sender method you don't need to instantiate a new instance of FirstViewController on each button press.

Answer 3

I have figured out a way to do this thanks to "#Gaurav Wadhwani" answer on this question: call method from other class (self issue).
I added this code in my FirstViewController.h:
+ (FirstViewController *)singletonInstance;
And then added this code in my FirstViewController.m
static FirstViewController *_singletonInstance = nil;
+(FirstViewController*)singletonInstance
{
#synchronized([FirstViewController class])
{
if (!_singletonInstance)
_singletonInstance = [[self alloc] init];
return _singletonInstance;
}
return nil;
}
+(id)alloc
{
#synchronized([FirstViewController class])
{
NSAssert(_singletonInstance == nil, #"Attempted to allocate a second instance of a singleton.");
_singletonInstance = [super alloc];
return _singletonInstance;
}
return nil;
}
Then I added this code in my SecondViewController to run the changeLabel method:
[[FirstViewController singletonInstance] changeLabel];
And that seems to work just fine so far. I hope it wont cause any other "problems" in the future, but right now it seems to be perfect.

Answer 4

Try doing this:
[label setNeedsDisplay];
After the last line in changeLabel.