iphone - 协议(protocol)方法未被调用，显示委托(delegate) 'nil'

Question

我正在开发 iPad 应用程序，但我遇到了委托(delegate)问题...协议(protocol)方法未被调用。我不确定我错过了什么，这是我的代码。

@protocol pickerLabelProtocol <NSObject>
- (void)selectedPickerData:(UILabel *)sender;
@end

@interface showPickerVC : UIViewController
@property (nonatomic, strong) id <pickerLabelProtocol> delegate;
@end

@implementation showPickerVC
- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
//i used breakpoint, the 'delegate' is always nil for some reason?
    [self.delegate selectedPickerData:self.mainLabel];
}

----------------------
@interface someViewController : UIViewController <pickerLabelProtocol>
@property (nonatomic, strong) showPickerVC *showPicker;
@end

@implementation someViewController

- (void)selectedPickerData:(UILabel *)sender
{
//protocol method
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.showPicker = [[showPickerVC alloc]init];
    self.showPicker.delegate = self;
}

Answer 1

我不会从你的代码中得到任何错误，但我建议你在创建 showPickerVC 的对象时清楚地添加它的 delegate self

比如，

showPickerVC *obj = [[showPickerVC alloc] init];
obj.delegate = self; /// YOur protocol delegate 
.
.
[self presentModalViewController:obj animated:YES];

同时添加如下代码

@implementation showPickerVC

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];

    if([self.delegate respondsToSelector:@selector(selectedPickerData:)])
    {
       [self.delegate selectedPickerData:self.mainLabel];
    }

}

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