iPhone - Call function from another view controller

Question

I have a function called sendDataToMotor. It is in my First View Controller classes. I have another view controller called SecondViewController. I need to call this function from the Second View Controller.m class. I tried declaring the property:

 @property(nonatomic,assign)UIViewController* firstController;

in my SecondViewController.h class. Furthermore, I wrote the code bellow in the viewDidLoad part of my SecondViewController.m class (where I want the function to be called).

secondViewController = [[SecondViewController alloc] initWithNibName:@"secondViewController" bundle:nil];
secondViewController.firstController = self;
[self.firstController performSelector:@selector(sendDataToMotor)];

But, Im getting an error with the first word in that code (secondViewController) because of an undeclared identifier issue. Furthermore, I get an error with the second line (secondViewController.firstController = self) because secondViewController has an unknown name type.

In summary, I don't care if you use the above code to answer my question: that was just something I tried to implement that I found online. However, I'm looking for the simplest way to call a function from another View Controller.

Answer 1

Notification Center could be solution to you question.

Receiver UIViewController

- (void)viewDidLoad {
    [[NSNotificationCenter defaultCenter] addObserver:self
        selector:@selector(receiveNotification:) 
        name:@"myNotification"
        object:nil];
}

- (void)receiveNotification:(NSNotification *)notification
{
    if ([[notification name] isEqualToString:@"myNotification"]) {
       //doSomething here.
    }
}

Sender UIViewController

- (void)sendNotification {
    [[NSNotificationCenter defaultCenter] postNotificationName:@"myNotification" object:self];
}

Answer 2

You want to use the delegate pattern, and you are almost there.

This line in secondVC:

 @property(nonatomic,assign)UIViewController* firstController;

should be generalised so as not refer to a specific type

 @property(nonatomic,weak)id <delegateProtocol> delegate;

And you should accompany that with a protocol declaration in the header of your secondVC (above the @interface declaration), something like

@protocol SecondVCDelegate
   - (void) sendDataToMotor;
@end

In firstVC interface you can declare your adherence to the delegate protocol in the first line of the @interface declaration in the header file

  @interface firstVC < SecondVCDelegate >

Or in the first line of a private interface declaration in the .m file

  @interface firstVC() < SecondVCDelegate >

Then you won't need to use performSelector (which anyway should be preceded by a safety check) as the compiler will alert you of errors.

In firstVC after creating secondVC, set it's delegate property to self(i.e. firstVC)

 secondVC.delegate = self;

then in secondVC you can just call the method directly on it's delegate:

[self.delegate sendDataToMotor];

I explain this in more (wordy) detail here...

https://stackoverflow.com/a/14910469/1375695

Answer 3

There are many problems in your code. I'm going to assume the second chunk of code you included is actually in -viewDidLoad in FirstViewController not the second.

1. The error you're getting is because you aren't putting the type before secondViewController. It should be SecondViewController *secondViewController = ...
2. This probably still won't work for you because when you perform your transition to the second view controller, you won't be using the same object.