如何使用協議Objective-C

Question

我需要將Picker選擇的值繼承到其他地方。我正在嘗試下面的代碼，但空值來了..請檢查我要去哪里。 我必須繼承在PickerView傳遞的String值。請檢查代碼

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

活動_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

您將在設置它之前打印出委托的值。...因此它將打印null。 您應該在調用didFinishPicking方法時打印出您的字符串，因為這是您設置字符串的地方。

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

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

請注意一側：避免使用任何帶有數字的名稱約定，例如Activity_1，Picker1，這是非常糟糕的代碼習慣。

Answer 2

在創建self.delegate1本身之前，您是NSLogging委托。請使用以下代碼行。

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

並將NSLog放入“ didFinishPicking”

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