Objective C Protocol Delegate test - objective-c

Question

I'm studing protocol and delegates using an Example! When I try to re create this example I notice that this condition is not respected:
if([delegate respondsToSelector:#selector(amountEntered:)]) {blabla}
where is the mistake? Scripts:
First View .h
#import <UIKit/UIKit.h>
#import "EnterAmountViewController.h"
#interface DelegateExampleViewController : UIViewController <EnterAmountDelegate>{
IBOutlet UILabel *amountLabel;
}
-(IBAction)changeAmountPressed;
#end
First View .m
#import "DelegateExampleViewController.h"
#implementation DelegateExampleViewController
-(IBAction)changeAmountPressed
{
EnterAmountViewController * enterAmountVC = [[EnterAmountViewController alloc]init];
enterAmountVC.delegate = self;
}
-(void)amountEntered:(NSInteger)amount
{
amountLabel.text = [NSString stringWithFormat:#"%i" , amount];
}
#end
Second View .h
#import <UIKit/UIKit.h>
#protocol EnterAmountDelegate <NSObject>
-(void)amountEntered:(NSInteger)amount;
#end
#interface EnterAmountViewController : UIViewController {
IBOutlet UITextField *amountTextField;
id<EnterAmountDelegate> delegate;
}
-(IBAction)savePressed;
#property(nonatomic,retain) id<EnterAmountDelegate> delegate;
#end
Second View .m
#import "EnterAmountViewController.h"
#import "DelegateExampleViewController.h"
#implementation EnterAmountViewController
#synthesize delegate;
- (void)viewDidLoad {
[super viewDidLoad];
amountTextField.text = #"";
[amountTextField becomeFirstResponder];
}
-(IBAction)savePressed
{
if([delegate respondsToSelector:#selector(amountEntered:)])
{
[delegate amountEntered:[amountTextField.text intValue]];
NSLog(#"rugg");
}
}
#end
Thanks in advance!

Answer 1

In the method:
-(IBAction)changeAmountPressed
{
EnterAmountViewController * enterAmountVC = [[EnterAmountViewController alloc]init];
enterAmountVC.delegate = self;
}
you are creating an instance of EnterAmountViewController on the stack as a local variable. This variable will be inaccessible at the end of the scope. So, when you execute savePressed you are doing it on a different object where you did not set delegate.
In other words, when you check
if([delegate respondsToSelector:#selector(amountEntered:)])
it returns NO because delegate is nil...
The correct way to set the delegate is using the prepareForSegue mechanism:
#implementation DelegateExampleViewController
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
[(EnterAmountViewController*)segue.destinationViewController setDelegate:self];
}
...
You do not need the changeAmountPressed method nor the relative binding.