Como usar os protocolos objective-c

Eu preciso herdar Picker valores selecionados para o outro lugar. Eu estou tentando o código abaixo, mas o valor nulo está chegando .. por favor, verifique onde estou indo errado. Eu tenho que Herdar valores String que tem sido passa noPickerView..por favor verifique o código

Picker1.h

#import <UIKit/UIKit.h>

@protocol pickerDelegate <NSObject>
-(void)didFinishPicking:(NSString *)pickedStr;

@end
@interface
@property(nonatomic,retain)id<pickerDelegate>delegate;

picker.m

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


 string=[NSString stringWithFormat:@"%@",[list objectAtIndex:row]];

 label.text=string;

 [self.delegate didFinishPicking:string];


}


- (void)viewDidLoad
 {
[super viewDidLoad];


list =[[NSMutableArray alloc]init];
[list addObject:@"a"];
[list addObject:@"b"];    

}

Acitivity_1.h

 #import <UIKit/UIKit.h>
#import "Picker1.h"
@interface Activity_1 : UIViewController<UIApplicationDelegate, pickerDelegate>{

@property(nonatomic,retain)Picker1 *delegate1;
@property (nonatomic,retain)NSString *str;

@end

Activity_1.m

- (void)viewDidLoad
{
[super viewDidLoad];
 **this is how i print the value but value is null**
 NSLog(@"delegate1%@",self.delegate1.string);


delegate1 = [[Picker1 alloc] init];

[delegate1 setDelegate : self];


}

-(void)didFinishPicking:(NSString *)pickedStr
{
[self setStr:pickedStr];
}

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