如何使用协议objective-c

Question

我需要将Picker选定的值继承到其他地方。我正在尝试下面的代码，但是null值即将到来。请检查我要出错的位置。 我必须继承被一直通过在PickerView ..please检查代码

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字符串值.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]; 
} 

Answer 1

创建self.delegate1本身 请使用的代码下面的行之前你NSLogging代表。

delegate1 = [[Picker1 alloc] init]; 
[delegate1 setDelegate : self]; 

并把NSLog的“didFinishPicking”

-(void)didFinishPicking:(NSString *)pickedStr 
{ 
NSLog(@"pickedStr%@", pickedStr); 
[self setStr:pickedStr]; 
} 

Answer 2

您打印出一个代表你设置它之前的值内....所以它会打印空。当你调用didFinishPicking方法时，你应该打印出你的字符串，因为这是你设置字符串的地方。

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

    // print the string you have just picked here if you want 
    NSLog(@"Picked string: %@",pickedStr); 
} 

注意一个侧面：避免任何名称约定与诸如Activity_1数，Picker1这是非常糟糕的代码实践。