Question

我正在尝试将SecondViewController指定为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获取消息并响应FirstViewController？（注意：我的SecondViewController负责一个带按钮的视图。当我按下SecondViewController视图上的按钮时，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

FirstViewController.m

#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

SecondViewController.h

#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

SecondViewController.m

#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
}

Answer 1

这有一些问题，看起来有些混乱。

我假设FirstViewController和SecondViewController位于标签栏控制器的单独选项卡中。

在sendPressed: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，以及为什么调用realLabel无效。

第二点是您似乎误解了委托的工作方式 - 您发布的代码中没有委托代理。

很好地阅读了与代表交流的内容：http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/CocoaFundamentals/CommunicatingWithObjects/CommunicateWithObjects.html

至于问题的解决方案，有几个选择：

从SecondViewController发布FirstViewController正在观察的通知（网上有很多关于通知的信息）。
在self.tabBarController.viewControllers数组中获取FirstViewController的特定实例，并从那里调用该方法。像......这样的东西。

- (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
}

有比这更多的选项，但上面的内容将为您提供一个良好的开端，为您的需求研究最佳方法。

希望这有帮助。

Xcode：委托对象是否必须向委托对象发送消息？

1 个答案: