在 iphone 的两个视图控制器之间使用委托

Question

我有两个视图控制器：视图控制器和 viewcontroller2nd。我在其中一个中有 UILabel，并且希望在单击 viewcontroller2nd 中的按钮（名为 Go）时更改它。我正在使用委托和协议来做到这一点。

代码如下所示：

ViewController.h

#import <UIKit/UIKit.h>
#import "ViewController2nd.h"

@interface ViewController : UIViewController <SecondViewControllerDelegate>
{
    IBOutlet UILabel *lbl;
    ViewController2nd *secondview;

}
-(IBAction)passdata:(id)sender;

@end

ViewController.m

#import "ViewController.h"
#import "ViewController2nd.h"

@interface ViewController ()

@end

@implementation ViewController

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

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
-(void) changeLabel:(NSString*)str{
    lbl.text = str;
}

-(IBAction)passdata:(id)sender{
    ViewController2nd *second = [[ViewController2nd alloc] initWithNibName:nil bundle:nil];
    [self presentViewController:second animated:YES completion:NULL];
}

@end

Viewcontroller2nd.h

#import <UIKit/UIKit.h>


@protocol SecondViewControllerDelegate <NSObject>
@optional
-(void) changeLabel:(NSString*)str;
@end

@interface ViewController2nd : UIViewController{

    IBOutlet UIButton *bttn;
    id <SecondViewControllerDelegate> delegate;

}

@property (retain) id delegate;

-(IBAction)bttnclicked;
-(IBAction)back:(id)sender;
@end

ViewController2nd.m

#import "ViewController2nd.h"
#import "ViewController.h"

@interface ViewController2nd ()

@end

@implementation ViewController2nd

@synthesize delegate;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

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

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

-(IBAction)bttnclicked{
   [[self delegate] changeLabel:@"Hello"];
}

-(IBAction)back:(id)sender{
    [self dismissViewControllerAnimated:YES completion:NULL];
}

@end

两个视图之间的控件传递工作正常。但是，当我单击 viewcontroller2nd 中的 go 按钮时，它不会将标签的值更改为 Hello。代码有什么问题？需要一些指导。

Answer 1

您似乎从未设置过委托。 您可以在您的 passData 方法中执行此操作：

-(IBAction)passdata:(id)sender{
    ViewController2nd *second = [[ViewController2nd alloc] initWithNibName:nil bundle:nil];
    second.delegate = self;
    [self presentViewController:second animated:YES completion:NULL];
}

Answer 2

嗯，在您的 changeLabel 委托方法中尝试以下操作：

-(void) changeLabel:(NSString*)str{
    lbl.text = str;
    [lbl setNeedsDisplay];
}

编辑：

除此之外： 你的标签是 IBOutlet，对吧？您是否在文件所有者的界面构建器中正确地将 xib 中的标签与 IBOutlet 属性（即 lbl）连接起来

Answer 3

如果您想通过使用委托来执行此操作，请更改 passdata 之类的：

 -(IBAction)passdata:(id)sender
  {
        ViewController2nd *second = [[ViewController2nd alloc] initWithNibName:nil bundle:nil];
        [second setDelegate:self];
        [self presentViewController:second animated:YES completion:NULL];
  }

您可以在没有委托的情况下执行此操作。 只需在 secondView 中创建一个 ViewController 的对象并像这样合成它：

#import "ViewController.h"
@interface ViewController2nd : UIViewController
{

    IBOutlet UIButton *bttn;
    ViewController  *parent;

}

@property (nonatomic, assign) ViewController  *parent;

-(IBAction)bttnclicked;
-(IBAction)back:(id)sender;
@end

并在passdata 中进行更改

-(IBAction)passdata:(id)sender
{
    ViewController2nd *second = [[ViewController2nd alloc] initWithNibName:nil bundle:nil];
    [second setParent:self];
    [self presentViewController:second animated:YES completion:NULL];
}

并将bttnclicked 更改为：

-(IBAction)bttnclicked
{
   [parent changeLabel:@"Hello"];
}

Answer 4

我为你写了以下内容！

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController

@property (strong, nonatomic) IBOutlet UILabel *label;

@end

#import "ViewController.h"
#import "ViewController2.h"

@interface ViewController () <ViewController2Delegate>

@end

@implementation ViewController

-(void)passdata:(NSString *)data
{
    self.label.text = data;
}

- (IBAction)buttonClicked:(id)sender {
    ViewController2 *v = [[ViewController2 alloc] initWithNibName:@"ViewController2" bundle:nil];
    v.delegate = self;
    [self presentViewController:v animated:YES completion:nil];
}

@end

#import <UIKit/UIKit.h>

@protocol ViewController2Delegate <NSObject>

- (void)passdata:(NSString*)data;

@end

@interface ViewController2 : UIViewController

@property(assign, nonatomic) id<ViewController2Delegate> delegate;

@end

#import "ViewController2.h"

@interface ViewController2 ()

@end

@implementation ViewController2

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (IBAction)buttonClicked:(id)sender {
    [self.delegate passdata:@"hello"];
}

- (IBAction)backButtonClicked:(id)sender {
    [self dismissViewControllerAnimated:YES completion:nil];
}

@end

Answer 5

• 您不需要在 ViewController.h 和 ViewController.m 中都导入头文件“ViewController2nd.h”
• 您声明的 UILabel 没有属性，例如 @property（强，非原子）。
• 可能是，您没有正确地将 UILabel 映射到您的 .storyboard 或 .xib 文件。

• 您在调用控制器时忘记分配第二个视图控制器委托

  ViewController2nd *second = [[ViewController2nd alloc] initWithNibName:nil bundle:nil];
  second.delegate = self;
  [self presentViewController:second animated:YES completion:NULL];
  

如果有人使用故事板进行视图控制器导航。

    - (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
    {
        if ([segue.identifier hasPrefix:@"view_to_capture"]) {
            ViewController2nd *destination = segue.destinationViewController;
            destination.delegate = self;
        }
    }