尝试学习objective-c委托.为什么我的示例项目不起作用

Question

我正在尝试在两个视图控制器之间传递数据。viewcontroller2是viewcontroller的委托。。笔记我称委托属性为"homie"是的，我知道这是一种糟糕的做法，但我只是在努力理解这个概念。

这是视图控制器：

#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

实现：

#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]];
    }
}

现在是实现第一个的另一个视图控制器

#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

实现：

#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

在viewdidload中，我实例化了第一个viewcontroller，并将自己设置为它的委托。我假设，当viewcontroller2在其方法中运行代码时，它将查看其委托是否实现了委托方法并使用该代码。。我在这里错过了什么？

Answer 1

您的问题是错误地使用了ViewControllers。您已初始化ViewController

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

接下来呢？你还没有把它分配给你的财产或其他什么。你做了什么？这很简单。您必须实现- (void)prepareForSegue:sender:。首先在你的故事板中设置segue的标识符。然后执行以下操作。

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

Answer 2

您需要在prepareForSegue 中设置委托

- (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
}