iOS 委托(delegate)取消调用失败

Question

我有两个 View Controller ，HomeViewController 和 AddViewController。 HomeViewController 是 AddViewController 的委托(delegate)。

问题是，当我在 AddViewController 中点击“取消”按钮时，对委托(delegate)的回调似乎没有执行。从症状上看，“取消”按钮的行为就好像它甚至没有连线一样。在编程上，断点似乎表明控制离开了 cancelButton 方法，但从未到达 addViewControllerDidCancel。

我相信一切都正确连接，这里是相关代码:

来自 AddViewController.h:

#import <UIKit/UIKit.h>
#import "WMDGCategory.h"
#import "WMDGActivity.h"
@class HomeViewController;


@protocol AddViewControllerDelegate <NSObject>

-(void) addViewControllerDidSave;

-(void) addViewControllerDidCancel:(WMDGActivity *) activityToDelete;

@end

@interface AddViewController : UIViewController <UIPickerViewDataSource,UIPickerViewDelegate>


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

来自 HomeViewController.h:

@interface HomeViewController : UITableViewController <UITableViewDataSource,UITableViewDelegate,AddViewControllerDelegate>

来自 HomeViewController.m:

-(void) addViewControllerDidSave
{
    NSManagedObjectContext *localContext = [NSManagedObjectContext MR_contextForCurrentThread];
    [localContext MR_saveToPersistentStoreAndWait];
    [self.navigationController dismissViewControllerAnimated:YES completion:nil];
    [self refreshData];

}

-(void) addViewControllerDidCancel:(WMDGActivity *) activityToDelete
{
    [activityToDelete MR_deleteEntity];
    [self.navigationController dismissViewControllerAnimated:YES completion:nil];
    [self refreshData];

}

来自 AddViewController.m:

- (IBAction)cancelButton:(UIBarButtonItem *)sender
{
    [self.delegate addViewControllerDidCancel:self.thisActivity];
}

有人能发现我的错误吗？

谢谢!

编辑以回应下面的答案 1:

实际上，我在 HomeViewController 的 prepareFroSegue 方法中这样做了:

- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
        NSManagedObjectContext *localContext = [NSManagedObjectContext MR_contextForCurrentThread];
    if ([[segue identifier] isEqualToString:@"addModal"])
    {
        UINavigationController *navController = (UINavigationController *)segue.destinationViewController;
        AddViewController *avc = (AddViewController *)navController.topViewController;
        avc.delegate = self;
        WMDGActivity *addedActivity = (WMDGActivity *)[WMDGActivity MR_createInContext:localContext];
        avc.thisActivity = addedActivity;
    }

}

Answer 1

您缺少分配 AddViewController 实例的委托(delegate)对象，据我所知，它仍然是 nil

myAddViewController.delegate = self;  // 'self' is an example, should be myHomeViewController instance

编辑:
您在代码中调用它:

[self.delegate addViewControllerDidCancel:self.thisActivity];

问问自己 delegate 的值(value)是什么？你已经声明了它，是的，但是你还没有设置它的值，所以它必须是nil。因此，当您实例化您的 AddViewController 时，您必须使用我之前编写的行设置委托(delegate)。