objective-c - NSDictionary 返回键的空值

Question

我无法理解为什么以下代码在控制台/终端中显示“The First Key = (null)”:

这是界面:

#import <UIKit/UIKit.h>

@interface TestingViewController : UIViewController

@property (nonatomic, strong) NSMutableArray *namesArray;
@property (nonatomic, strong) NSDictionary *myDictionary; 

@end

这是实现:

#import "DictionaryTestViewController.h"

@implementation DictionaryTestViewController

@synthesize namesArray;
@synthesize myDictionary;

- (void)viewDidLoad
{
    [super viewDidLoad];

    [self.myDictionary initWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];
    NSLog(@"The First Key = %@", [self.myDictionary objectForKey:@"key1"]);
}

@end

提前致谢!

Answer 1

您还没有分配字典。目前是 nil，向 nil 发送消息什么也不做。

如果您使用的是 ARC，请将其改为此

self.myDictionary = [[NSDictionary alloc] initWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];

如果不是这样

self.myDictionary = [[[NSDictionary alloc] initWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil] autorelease];