Question

基本上，我现在打算使用委托在视图控制器之间传递值。

视图控制器的流程是A - ＆gt; B - ＆gt; C使用push segue。

当用户在＆＃34; C＆＃34;视图控制器，如何将值BACK传递给第一个视图控制器，即＆＃34; A＆＃34;？

在我的代码中，＆＃34; self.delegate＆＃34;始终为nil，并且永远不会触发委托方法。

以下是第一个VC和第三个VC的代码：

第一个VC .m：

#import "ViewController.h"
#import "ThirdViewController.h"

@interface ViewController ()<PassValueProtocal>
@property (weak, nonatomic) IBOutlet UILabel *myLabel;

@end

@implementation ViewController
{
    ThirdViewController *thirdVC;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void) passValueBack:(NSString *)value
{
    NSLog(@"HAHAH");
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


- (IBAction)segueToSecondVC:(UIButton *)sender
{
    thirdVC = [ThirdViewController sharedManager];

    thirdVC.delegate = self;
}

@end

第三VC .h：

#import <UIKit/UIKit.h>

@protocol PassValueProtocal <NSObject>
- (void) passValueBack: (NSString *) value;
@end

@interface ThirdViewController : UIViewController

@property (weak, nonatomic) id<PassValueProtocal>delegate;
+ (id) sharedManager;

@end

第三个VC .m：

#import "ThirdViewController.h"

@interface ThirdViewController ()
@property (weak, nonatomic) IBOutlet UITextField *myTextField;

@end

@implementation ThirdViewController

+ (id) sharedManager
{
    NSLog(@"myDelegate sharedManager");
    static ThirdViewController *sharedManager = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{ sharedManager = [[self alloc] init]; });
    return sharedManager;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)passValueAction:(UIButton *)sender
{
    NSLog(@"%@", self.delegate);
    if ([self.delegate respondsToSelector:@selector(passValueBack:)])
    {
        [self.delegate passValueBack:self.myTextField.text];
    }
}


@end

Answer 1

您的代码

- (IBAction)segueToSecondVC:(UIButton *)sender
{
    thirdVC = [ThirdViewController sharedManager];

    thirdVC.delegate = self;
}

不应该在这里。您应该实现函数prepareForSegue并将此代码移动到那里。像

这样的东西

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
ThirdViewController *thirdVC = (ThirdViewController *)segue.destinationViewController;
thirdVC.delegate = self;

}

委托不响应选择器

1 个答案: