試圖學習Objective-C的代表。爲什麼我的示例項目不工作？

Question

我想在兩個視圖控制器之間傳遞數據。 viewcontroller2是viewcontroller的一個委託.. note ..我叫委託屬性「homie」是的，我知道這是不好的做法，但我只是在試圖理解這個概念。

這裏是視圖 - 控制：

#import <UIKit/UIKit.h> 
@protocol ViewControllerDelegate <NSObject> 
@required 
- (void)sendData:(NSString *)theString; 
@end 

@interface ViewController : UIViewController 
@property (nonatomic, assign) id <ViewControllerDelegate> homie; 
- (void)doSomething; 
- (IBAction)doneText:(id)sender; 

@end 

實現：

#import "ViewController.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)doSomething{ 
} 

- (IBAction)doneText:(id)sender { 
    UITextField *thisField = sender; 

    if([_homie respondsToSelector:@selector(sendData:)]){ 
     [_homie sendData:[thisField text]]; 
    } 
} 

現在這裏是實施第一

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

@interface ViewController2 : UIViewController <ViewControllerDelegate> 

- (IBAction)hittingbtn:(id)sender; 

@property (weak, nonatomic) IBOutlet UITextField *textfield; 
@property (strong, nonatomic) ViewController *vc; 

@end 

執行其他視圖控制器：

#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; 
} 

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    ViewController *theview = [[ViewController alloc]init]; 
    theview.homie = self; 

    // Do any additional setup after loading the view. 
} 

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


// DELEGATE METHOD 
- (void)sendData:(NSString *)theString{ 
    [_textfield setText:theString]; 
} 

- (IBAction)hittingbtn:(id)sender { 
} 
@end 

in viewdidload我實例化第一個viewcontroller，並將自己設置爲它的委託。即時假設然後當viewcontroller2在其方法中運行代碼，然後它會看到它的委託是否實現了委託方法並使用該代碼..我在這裏失蹤了什麼？

Answer 1

你的問題是你使用ViewControllers錯誤。您已初始化ViewController

ViewController *theview = [[ViewController alloc]init]; 
theview.homie = self; 

下一步是什麼？你還沒有把它分配給你的財產或什麼。你做了什麼？這很簡單。您必須執行- (void)prepareForSegue:sender:。首先在你的故事板中設置segue的標識符。然後做下面的事。

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender 
{ 
    if ([[segue identifier] isEqualToString:@"MySegue"]) { 
     ViewController *destinationViewController = (ViewController *)[segue destinationViewController]; 
     ViewController.homie = self; 
    } 
} 

Answer 2

您需要設置委託在prepareForSegue

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender 
{ 
    if ([segue.destinationViewController respondsToSelector:@selector(setHomie)]) { 
     [segue.destinationViewController setHomie:self]; 
    //or 
    if ([[segue.destinationViewController isKindOfClass:[ViewController class]]) { 
     ViewController *destinationViewController = (ViewController *)[segue destinationViewController]; 
     ViewController.homie = self; 
    } 
    //or the segue identifier which has already been mentioned 
}