xcode 在对象“AddEventViewController”上找不到属性“delegate”
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Property 'delegate' not found on object 'AddEventViewController'
提问by Solid I
With the help of the Developer Library, I am trying to work with the EventKit and EventKitUI Frameworks. I've hit a very early roadblock. I have copied and pasted code from the library found here. I have added a view controller called 'AddEventViewController' a button to the Navigation Bar in my ViewController and I am using this code to invoke it.
在开发人员库的帮助下，我正在尝试使用 EventKit 和 EventKitUI 框架。我很早就遇到了障碍。我已经从这里找到的库中复制并粘贴了代码。我在 ViewController 的导航栏中添加了一个名为“AddEventViewController”的视图控制器，我正在使用此代码来调用它。
- (IBAction)add:(id)sender {
AddEventViewController *addController = [[AddEventViewController alloc]
init];
addController.delegate = self;
UINavigationController *navigationController = [[UINavigationController alloc]
initWithRootViewController:addController];
[self presentViewController:navigationController animated:YES completion: nil];
}
}
The error shows on line: addController.delegate = self;
在线显示错误： addController.delegate = self;
This code is copied straight from the Library. I am using Xcode 4.2 and a Storyboard if that might help.
此代码直接从库中复制。如果可能有帮助，我正在使用 Xcode 4.2 和 Storyboard。
UPDATE: This is AddEventViewController.h:
更新：这是 AddEventViewController.h：
#import <UIKit/UIKit.h>
@interface AddEventViewController : UIViewController
@end
You're going to tell me I created this ViewController incorrectly? Please explain why just not "how" if you'd be so nice?
你会告诉我我错误地创建了这个 ViewController 吗？请解释一下，如果你这么好，为什么不“如何”？
回答by Rob Napier
I see how Apple's example here has likely confused you here. First, download the full source for iPhoneCoreDataRecipes(or at least reference it while trying to understand this code).
我看到这里 Apple 的例子很可能让你感到困惑。首先，下载iPhoneCoreDataRecipes的完整源代码（或至少在尝试理解此代码时参考它）。
To really understand what's going on here, you need to read on down to the section called "Dismissing a Presented View Controller" and then follow the link to "Use a Delegation to Communicate With Other Controllers." ("a Delegation?" Very strange....)
要真正理解这里发生的事情，您需要继续阅读名为“解除呈现的视图控制器”的部分，然后点击“使用委派与其他控制器进行通信”的链接。（“一个代表团？”很奇怪……）
So here's what's going on. The presented view has a "delegate" which is the object it's supposed to tell "interesting" things to. In this case, "interesting" things are "hey, I added a recipe!" To achieve this, the delegate implements a protocol, which just means it promises to implement some methods. In this case, the required method is recipeAddViewController:didAddRecipe:.
这就是正在发生的事情。呈现的视图有一个“委托”，它是它应该告诉“有趣”事物的对象。在这种情况下，“有趣”的事情是“嘿，我添加了一个食谱！” 为了实现这一点，委托实现了一个协议，这意味着它承诺实现一些方法。在这种情况下，所需的方法是recipeAddViewController:didAddRecipe:。
AddViewControllerhas a delegateproperty like this:
AddViewController有这样的delegate属性：
@property(nonatomic, assign) id <RecipeAddDelegate> delegate;
That just means that the delegate must conform to the named protocol. The delegate itself indicates that it does so in its interface:
那只是意味着委托必须符合命名协议。委托本身表明它在其界面中这样做：
@interface RecipeListTableViewController : UITableViewController <RecipeAddDelegate, NSFetchedResultsControllerDelegate> {
Note that this is marked assignfor reasons @Yuras explains. But if you're writing new code targeted at iOS 5, you should use weakinstead of assign. weakproperties are automatically set to nilif their referenced object is deallocated. It's just safer that way. No dangling pointers.
请注意，这是assign出于@Yuras 解释的原因标记的。但是，如果你在iOS 5的编写有针对性的新的代码，你应该使用weak代替assign。如果它们的引用对象被释放weak，nil则属性会自动设置为。那样只会更安全。没有悬空的指针。
回答by Yuras
In Objective-C any property you are using should be declared somewhere. Any properties, that are declared in parent class (UIViewControllerin your case) are inherited by all the derived classes (AddEventViewControllerin your case).
在 Objective-C 中，您使用的任何属性都应该在某处声明。在父类（UIViewController在您的情况下）中声明的任何属性都由所有派生类（AddEventViewController在您的情况下）继承。
AddEventViewControllerinherits UIViewController, but the delegateproperty is not declared neither in the first, nor in the second. That is why compiler is not happy.
AddEventViewControllerinherits UIViewController，但该delegate属性既未在第一个中声明，也未在第二个中声明。这就是编译器不高兴的原因。
You should declare it. Something like the next:
你应该申报。类似下一个：
@interface AddEventViewController : UIViewController
@property (nonatomic, assign) id delegate;
@end
@implementation AddEventViewController
@synthesize delegate;
@end
Delegates are usually declared with assignattribute to prevent circle retains (e.g. Aretains Band Bretains A)
委托通常用assign属性声明以防止循环保留（例如A保留B和B保留A）
