声明委托属性时出错

Question

This should be an easy question - but I'm having a hard time figuring it out. I'm trying to create a property on an object so that during prepareForSegue I can tell the object what it's delegate is. I know I could do this with protocols but I figured for this case a direct approach would be simplest. Unfortunately, the following code results in a compiler error:

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

@interface DepartmentViewController : UITableViewController

@property (nonatomic, weak) PlanningViewController *planningDelegate;

@end

When I type the property declaration, Xcode recognizes PlanningViewController and even displays the text for me to just tab through. The compiler, though, complains with:

Unknown type name 'PlanningViewController': did you mean 'UISplitViewController'?

What am I doing wrong?

PlanningViewController.h looks like this:

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

@interface PlanningViewController : UITableViewController


// Table cell connections
- (IBAction)addItemPressed:(id)sender;


@end

Answer 1

Remove this line from your PlanningViewController.h header file:

#import "DepartmentViewController.h"

You have something of a loop in your header files.

Better still, make DepartmentViewController.h look like this (there is no need to include PlanningViewController.h in your header file):

#import <UIKit/UIKit.h>

@class PlanningViewController;

@interface DepartmentViewController : UITableViewController

@property (nonatomic, weak) PlanningViewController *planningDelegate;

@end

Answer 2

I think you've kind of missed one of the main points of the delegate patter which is to decouple you objects. The best way of declaring this delegate would be:

#import <UIKit/UIKit.h>

@protocol DepartmentViewControllerDelegate; // forward declaration of protocol

@interface DepartmentViewController : UITableViewController

@property (nonatomic, weak) id <DepartmentViewControllerDelegate> delegate;

@end

@protocol DepartmentViewControllerDelegate
- (void)departmentViewController:(DepartmentViewController *)controller
              isProcessingPeople:(NSArray *)people
@end

In your department view controller, you would then write something like this:

if ([self.delegate respondsToSelector:@selector(departmentViewController:isProcessingPeople:)]) {
    [self.delegate departmentViewController:self isProcessingPeople:people];
}

And in your planning view controller, you would implement this method:

- (void)departmentViewController:(DepartmentViewController *)controller
              isProcessingPeople:(NSArray *)people {
    // do necessary work here
}

The example here is just an example of one message you can send to the delegate. You can add whatever you need, but this makes it so there is no coupling between your controllers. The planning view controller knows everything it needs to about the department controller, but the department controller doesn't need to know anything about the planning controller.

If you want to stick with what you have currently, just recognize that it's not really the delegate pattern, and you should probably rename your property.