iOS use the delegate pass value not trigger the method - ios

Question

I was test the delegate pass the value in objective-c.
I know there are other methods can pass string between UIViewControllers like NSNotifyCenter..etc.
Now I want to try to use the delegate pass value .
But I encounter some problems.
I use the navigation and there have two UIViewController(FirstUIViewcontroller and SecondUIViewController).
Now I want to use manual to change to SecondUIViewController,not use the button drag to the SecondUIViewController at FirstUIViewController.
So I add the code in the FirstUIViewController.m button action.
- (IBAction)pushBtnAction:(id)sender {
SecondViewController *controller = [self.storyboard instantiateViewControllerWithIdentifier:#"SecondViewController"];
[self.navigationController pushViewController:controller animated:YES];
}
Then I want to pass the value from the SecondUIViewcontroller when I pop the view controller.
So I add the delegate implement and se the delegate in the FirstUIViewController.m.
- (void)viewDidLoad {
[super viewDidLoad];
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:#"Main" bundle: nil];
secondVC = (SecondViewController*)[mainStoryboard instantiateViewControllerWithIdentifier:#"SecondViewController"];
secondVC.delegate = self;
}
-(void) passSecondVC:(SecondViewController *)vc didAddValue:(NSString *)str
{
NSLog(#"second str:%#",str);
}
In the SecondUIViewController.h , I had declare delegate method.
#class SecondViewController;
#protocol SecondViewControllerDelegate <NSObject>
#optional
-(void)passSecondVC:(SecondViewController*)vc didAddValue:(NSString*) str;
#end
#interface SecondViewController : UIViewController
#property (nonatomic,assign) id<SecondViewControllerDelegate> delegate;
- (IBAction)passValueDelegatBtnAction:(id)sender;
In the SecondViewController.m ,
when I click the button will pop self uiviewcontroller and pass the value to FirstUIViewController.
- (IBAction)passValueDelegatBtnAction:(id)sender {
if( [self.delegate respondsToSelector:#selector(passSecondVC:didAddValue:)])
{
[self.delegate passSecondVC:self didAddValue:#"this is string from sencond vc"];
}
[self.navigationController popViewControllerAnimated:YES];
}
(My problems)
But in this status , I always can't get the value in the delegate method in the FirstUIViewController.
I had try to other method like below in the FirstViewController.m
- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
NSLog(#"segue");
id vc = segue.destinationViewController;
if( [vc isKindOfClass:[SecondViewController class]])
{
SecondViewController *secondVC = vc;
secondVC.delegate = self;
}
}
There are same problem.
I can't get the value from the delegate method.
Have anyone know where the problems?
I post my completely code in here.
Thank you very much.

Answer 1

Alright!
Remove your code from the viewDidLoad: method and set the delegate when you push the secondViewController.
- (IBAction)pushBtnAction:(id)sender {
SecondViewController *controller = [self.storyboard instantiateViewControllerWithIdentifier:#"SecondViewController"];
[controller setDelegate:self];
[self.navigationController pushViewController:controller animated:YES];
}
So what was going wrong?
Ans: You create a new object in your viewDidLoad: method and set your firstViewController as delegate to it. Now while pushing you are creating another object of SecondViewController whose delegate is not set.

Answer 2

I downloaded your code & fixed it.
You don't want this line. so comment it,
// UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:#"Main" bundle: nil];
// secondVC = (SecondViewController*)[mainStoryboard instantiateViewControllerWithIdentifier:#"SecondViewController"];
// secondVC.delegate = self;
Edit this method as below,
- (IBAction)pushBtnAction:(id)sender {
SecondViewController *controller = [self.storyboard instantiateViewControllerWithIdentifier:#"SecondViewController"];
controller.delegate = self;
[self.navigationController pushViewController:controller animated:YES];
}
Also edit this method as below,
- (IBAction)passValueDelegatBtnAction:(id)sender {
// if( [self.delegate respondsToSelector:#selector(passSecondVC:didAddValue:)])
// {
[self.delegate passSecondVC:self didAddValue:#"this is string from sencond vc"];
// }
[self.navigationController popViewControllerAnimated:YES];
}

Answer 3

you forgot some code in pushBtnAction..
- (IBAction)pushBtnAction:(id)sender {
SecondViewController *controller = [self.storyboard instantiateViewControllerWithIdentifier:#"SecondViewController"]; // It's different to VC you init in viewDidLoad
controller.delegate = self; // you forgot....
[self.navigationController pushViewController:controller animated:YES];
}
prepareForSegue be call when you use segue to navigation.