iPhone 委托错误

Question

我有 2 个观点。 firstView 和 secondView。 firstView 需要来自 secondView 的 favorites 数组，因此我尝试调用协议中定义的 getFavourites 方法。然而，这返回 null，这对我来说似乎很奇怪，因为一切都是有道理的。

这是 firstViewController.h：

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

@protocol firstViewControllerDelegate;

@interface FirstViewController : UIViewController
{
    id <firstViewControllerDelegate> delegate;
    NSMutableArray *labels;

    UIButton *button1;
    UIButton *button2;
    UIButton *button3;
    UIButton *button4;
}

- (IBAction) buttonClick: (id) sender;

@property (nonatomic, assign) id <firstViewControllerDelegate> delegate;
@property (nonatomic, retain) IBOutlet UIButton *button1;
@property (nonatomic, retain) IBOutlet UIButton *button2;
@property (nonatomic, retain) IBOutlet UIButton *button3;
@property (nonatomic, retain) IBOutlet UIButton *button4;

@end

@protocol firstViewControllerDelegate
- (NSMutableArray *) getFavourites;
- (void) setFavourites: NSMutableArray;
@end

firstViewController.m

@synthesize delegate;

.......

- (void) viewWillAppear:(BOOL)animated
{
    NSMutableArray *favourites = [delegate getFavourites]; // favourites is empty after this line
    [button1 setTitle:[[favourites objectAtIndex:1] name] forState:UIControlStateNormal];
    NSLog(@"VIEW APPEARED. BUTTON TITLE IS: %@", button1.currentTitle);
}

SecondViewController.h

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

@interface SecondViewController: UIViewController <UITableViewDelegate, UITableViewDataSource, UITextFieldDelegate, firstViewControllerDelegate>
{
        NSMutableArray *favourites;
        NSMutableArray *drinks;
}

@property (nonatomic, retain) NSMutableArray *drinks;
@property (nonatomic, retain, getter = getFavourites) NSMutableArray *favourites;

- (void) addDrink: (NSString *) name;

@end

有人知道为什么这不起作用吗？

Answer 1

您确定要设置 FirstViewController 的委托属性吗？即：

FirstViewController *firstController = // Instantiate the controller;
firstController.delegate = secondController;
[self.navigationController pushViewController:firstController animated:YES];

secondController 应该在实例化之前存在，否则您将设置一个 nil 值