NSDictionary基本概念

2024-09-04 06:57:38

1.NSDictionar基本概念

什么是NSDictionary
- NSDictionary翻译过来叫做”字典”
- 日常生活中,“字典”的作用:通过一个拼音或者汉字,就能找到对应的详细解释
- NSDictionary的作用类似:通过一个key,就能找到对应的value
- NSDictionary是不可变的, 一旦初始化完毕, 里面的内容就无法修改

2.NSDictionary的创建

+ (instancetype)dictionary;

+ (instancetype)dictionaryWithObject:(id)object forKey:(id <NSCopying>)key;

+ (instancetype)dictionaryWithObjectsAndKeys:(id)firstObject, ...;

+ (id)dictionaryWithContentsOfFile:(NSString *)path;

+ (id)dictionaryWithContentsOfURL:(NSURL *)url;

NSDictionary创建简写

　　　以前

NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:@"lnj", @"name", @"12345678", @"phone", @"天朝", @"address", nil];

　　　现在

NSDictionary *dict = @{@"name":@"lnj", @"phone":@"12345678", @"address":@"天朝"};

NSDictionary获取元素简写

　　　以前

[dict objectForKey:@"name”];

　　　现在

dict[@"name”];

键值对集合的特点

字典存储的时候,必须是"键值对"的方式来存储(同时键不要重复)
键值对中存储的数据是"无序的".
键值对集合可以根据键, 快速获取数据.

3.NSDictionary的遍历

- (NSUInteger)count;
- 返回字典的键值对数目
- (id)objectForKey:(id)aKey;
- 根据key取出value

快速遍历

    NSDictionary *dict = @{@"name":@"lnj", @"phone":@"12345678", @"address":@"天朝"};

    for (NSString *key in dict) {

        NSLog(@"key = %@, value = %@", key, dict[key]);

    }

Block遍历

   [dict enumerateKeysAndObjectsUsingBlock:^(NSString *key, NSString *obj, BOOL *stop) {

        NSLog(@"key = %@, value = %@", key, obj);

    }];

4.NSDictionary文件操作

将字典写入文件中
- - (BOOL)writeToFile:(NSString *)path atomically:(BOOL)useAuxiliaryFile;
- - (BOOL)writeToURL:(NSURL *)url atomically:(BOOL)atomically;
- 存结果是xml文件格式,但苹果官方推荐为plist后缀。
示例

    NSDictionary *dict = @{@"name":@"lnj", @"phone":@"12345678", @"address":@"天朝"};

    BOOL flag = [dict writeToFile:@"/Users/LNJ/Desktop/dict.plist" atomically:YES];

    NSLog(@"flag = %i", flag);

从文件中读取字典

NSDictionary *newDict = [NSDictionary dictionaryWithContentsOfFile:@"/Users/LNJ/Desktop/dict.plist"];

    NSLog(@"newDict = %@", newDict);

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