Xcode：委托对象是否必须向委托对象发送消息？
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我正在尝试将SecondViewController分配为FirstViewController的委托对象（如果我理解正确的话）。但是，FirstViewController不会向SecondViewController发送任何消息。
我是否可以假装SecondViewController确实从FirstViewController收到消息并响应FirstViewController？ （注意：我的SecondViewController负责一个具有按钮的视图。当我在SecondViewController的视图上按下按钮时，我希望它告诉FirstViewController更新其视图）
FirstViewController.h
#import <UIKit/UIKit.h>
@protocol FirstViewControllerDelegate <NSObject>
@optional
- (void) setAnotherLabel;
@end
@interface FirstViewController : UIViewController {
IBOutlet UILabel *label;
id <FirstViewControllerDelegate> delegate;
}
@property (nonatomic, retain) IBOutlet UILabel *label;
@property (nonatomic, assign) id <FirstViewControllerDelegate> delegate;
- (void) pretendLabel;
- (void) realLabel;
@end
#import \"FirstViewController.h\"
@implementation FirstViewController
@synthesize label;
@synthesize delegate;
// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void) setAnotherLabel;
{
label.text =@\"Real\";
[self.view setNeedsDisplay];
}
- (void) pretendLabel;
{
label.text =@\"Pretend\";
[self.view setNeedsDisplay];
}
- (void) realLabel;
{
[self setAnotherLabel];
}
- (void)viewDidLoad
{
[super viewDidLoad];
label.text=@\"Load\";
[self pretendLabel];
}
...
@end
#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#import \"FirstViewController.h\"
@interface SecondViewController : UIViewController <UIImagePickerControllerDelegate, UINavigationControllerDelegate, FirstViewControllerDelegate>
{
UIImage *image;
IBOutlet UIImageView *imageView;
}
- (IBAction) sendPressed:(UIButton *)sender;
- (IBAction) cancelPressed:(UIButton *)sender;
@end
#import \"SecondViewController.h\"
@implementation SecondViewController
- (IBAction) sendPressed:(UIButton *)sender
{
FirstViewController *fvc = [[FirstViewController alloc] init];
[fvc setDelegate:self];
//how do I find out if I\'m actually the delegate for FirstViewController at this point?
[fvc realLabel];
self.tabBarController.selectedIndex = 0;//switch over to the first view to see if it worked
}
没有找到相关结果
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1 个回复
导力疵谜
方法中，您正在创建FirstViewController的新实例-这与标签栏控制器中的FirstViewController不同，为什么调用and5ѭ无效。 第二点是您似乎误解了委托的工作原理-在发布的代码中没有理由要委托。 阅读有关与代表打交道的好书：http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/CocoaFundamentals/CommunicatingWithObjects/CommunicateWithObjects.html 至于您的问题的解决方案，有几种选择： 从SecondViewController发布一个FirstViewController正在观察的通知（网络上有关通知的大量信息）。 在self.tabBarController.viewControllers数组中获取FirstViewController的特定实例，然后从那里调用该方法。就像是...- (IBAction) sendPressed:(UIButton *)sender { for(UIViewController *controller in self.tabBarController.viewControllers) { if([controller isKindOfClass:[FirstViewController class]]) { FirstViewController *firstViewController = (FirstViewController *)controller; [firstViewController realLabel]; } } self.tabBarController.selectedIndex = 0;//switch over to the first view to see if it worked }