iOS7 在导航 Controller 推送 View 设置中按协议(protocol)向后传递数据

Question

我在我的代码中尝试了许多自定义委托(delegate)示例，将数据从 View B 发送回父 View A。为什么我得到 NULL？应该有一些我想念的东西。请帮忙。我如何调用 setupDate 以在父 View 中接收 (NSDate *)setAlarmDate？

父 View

#import "SetupViewController.h"

@interface ViewController : UIViewController <SetupViewControllerDelegate> {
NSTimer *timer;
}
@end

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController
-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender{
if ([[segue identifier] isEqualToString:@"setupview"]) {
    NSLog(@"prepare for segue");
    SetupViewController *svc = [[SetupViewController alloc] init];
    svc.delegate = self;

-(void)setupDate:(NSDate *)setAlarmDate{
NSLog(@"Hey Hey");
NSLog(@"%@", setAlarmDate);
}
@end

View B

@protocol SetupViewControllerDelegate <NSObject>
@required
-(void)setupDate:(NSDate *)setAlarmDate;
@end

@interface SetupViewController : UIViewController
@property (nonatomic, strong) id <SetupViewControllerDelegate> delegate;
//IB
@property (weak, nonatomic) IBOutlet UIDatePicker *pDatePicker;
@end

.m

#import "SetupViewController.h"
#import "ViewController.h"
@implementation SetupViewController
-(void)viewWillDisappear:(BOOL)animated{
NSDate *date = [self.pDatePicker date];
[[self delegate] setupDate:date];
}
@end

Answer 1

您应该使用 segue 的 destinationViewController 属性访问 UIViewController 而不是分配您自己的实例，这就是为什么您的 alarmDate = NULL .

例如

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([[segue identifier] isEqualToString:@"setupview"])
    {
        NSLog(@"prepare for segue");
        SetupViewController *svc = [segue destinationViewController];
        svc.delegate = self;
    }
}

此外，正如@Neru 提到的，您的代理人应该是弱者而不是强者。这样做的原因是如果你没有在 dealloc 方法中显式设置 delegate = nil ，你将导致一个 retain cycle。