如何使用协议Objective-C

Question

我需要将Picker选择的值继承到其他地方。我正在尝试下面的代码，但空值来了..请检查我要去哪里。 我必须继承在PickerView传递的String值。请检查代码

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.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

活动_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

您将在设置它之前打印出委托的值。...因此它将打印null。 您应该在调用didFinishPicking方法时打印出您的字符串，因为这是您设置字符串的地方。

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

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

请注意一侧：避免使用任何带有数字的名称约定，例如Activity_1，Picker1，这是非常糟糕的代码习惯。

Answer 2

在创建self.delegate1本身之前，您是NSLogging委托。请使用以下代码行。

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

并将NSLog放入“ didFinishPicking”

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