Question

The setup:

PickerView (spinSelector) and label (chosenItem) added to ViewController.
Created separate delegate class files (SpinDelegate m&h) for the PickerView delegate.
Created instance of the delegate (SpinDelegate *mySpinDelegate)
Assigned delegate property to delegate instance

ViewController.h

@interface ViewController : UIViewController
{
    SpinDelegate *mySpinDelegate;
}

@property (nonatomic, weak) IBOutlet UILabel *chosenItem;
@property (nonatomic, strong) IBOutlet UIPickerView *spinSelector;

ViewController.m

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    mySpinDelegate=[[SpinDelegate alloc]init];

    self.spinSelector.delegate=mySpinDelegate;
    self.spinSelector.dataSource=mySpinDelegate;
}

SpinDelegate.h

@interface SpinDelegate : UIViewController <UIPickerViewDataSource, UIPickerViewDelegate>
{
    ChoiceData *choiceItems;
}

@end

SpinDelegate.m

    #pragma mark - PickerView Delegate
    - (NSString *)pickerView:(UIPickerView *)pickerView 
titleForRow:(NSInteger)row 
forComponent:(NSInteger)component{

        return [choiceItems.choiceList objectAtIndex:row];
    }

Next is to use the method:

- (void)pickerView:(UIPickerView *)pickerView didSelectRow:(NSInteger)row inComponent:(NSInteger)component;

This is part of the UIPickerViewDelegate protocol. Using this, to simply change the UILabel (chosenItem) in the ViewController to value of row. Something like “The picked item is %i”,row

I’ve read and searched through a ton of posts and questions on UIViewController to UIViewController messaging and looked at protocol/delegate, singleton, NSNotificationCenter… it just seems to me that there is a syntax I am missing to address the parent/super? The ViewController created the instance of the delegate, doesn’t the delegate have scope?

Please educate me on this. : )

Answer 1

You can do something like this:

ViewController.h

#import "SpinViewController.h"
@interface ViewController : UIViewController<SpinViewControllerDelegate>
{
}

@property (nonatomic, weak) IBOutlet UILabel *chosenItem;
@property (nonatomic, strong) IBOutlet UIPickerView *spinSelector;

ViewController.m

- (void)someFunction
{
    mySpinViewController=[[SpinViewController alloc]init];
    mySpinViewController.delegate=self;
    // show or present mySpinViewController
}

//implement the followed protocol's method
-(void) optionSelected:(NSString*)cellValue{

}

SpinViewController.h

@protocol SpinViewControllerDelegate <NSObject>

@optional
-(void) optionSelected:(NSString*)cellValue;
@end

@interface SpinViewController : UIViewController <UIPickerViewDataSource, UIPickerViewDelegate>
{
    ChoiceData *choiceItems;
}

@property (nonatomic,retain)id <SpinViewControllerDelegate> delegate;

@end

SpinViewController.m

-(void) pickerValueSelectedOrSimilarFn:(NSString*)cellValue{
  // this is how you give a callback to classes following the protocol
  [self.delegate optionSelected:cellValue];
}