iphone - 如何使用协议objective-c

Question

我需要将 Picker 选择的值继承到另一个地方。我正在尝试下面的代码，但 null 值即将到来..请检查我哪里出错了。我必须继承传入的字符串值PickerView..请检查代码

选择器1.h

#import <UIKit/UIKit.h>

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

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

选择器.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"];    

}

活动_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

您在设置委托之前打印出委托的值......所以它将打印空值。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);
}

请注意一方面：避免任何带有数字的命名约定，例如 Activity_1、Picker1，这是非常糟糕的代码实践。

Answer 2

在创建 self.delegate1 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];
}