Foundation框架--NSDictionary的使用

一、NSDictionary介绍

1、NSDictionary的介绍

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(键), 就能找到对应的value(值) NSDictionary是不可变的, 一旦初始化完毕, 里面的内容就无法修改。

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2、NSDictionary的创建

1)创建空字典

NSDictionary *d1 = [NSDictionary dictionary];NSLog(@"d1 = %@",d1);

打印结果：
d1 = {
}

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2)创建只有一组键值对的字典

NSDictionary *d2 = [NSDictionary dictionaryWithObject:@"jiaozuo" forKey:@"H"];NSLog(@"d2 = %@",d2);

打印结果：

d2 = {
H = jiaozuo;
}

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3)创建多组键值对的字典

NSDictionary *d3 = [NSDictionary dictionaryWithObjectsAndKeys:@"jiaozuo",@"H",@"zhengzhou",@"A",@"luoyang",@"C", nil];NSLog(@"d3 = %@",d3);

打印结果：

d3 = {
A = zhengzhou;
C = luoyang;
H = jiaozuo;
}

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4)快速创建一个字典@{key值：value值}

NSDictionary *d4 = @{                             @"S":@"dazhou",@"A":@"chengdu"                    };NSLog(@"d4 = %@",d4);

打印结果：

d4 = {
A = chengdu;
S = dazhou;
}

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3、键值对集合的特点

1）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)

2） 键值对中存储的数据是”无序的”.

3） 键值对集合可以根据键, 快速获取数据.

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二、NSDictionary基本使用方法

1、获取字典长度

NSLog(@"d4.count = %lu",d4.count);

打印结果：

d4.count = 2

2、根据key值取出value值

NSString *str1 = [d4 valueForKey:@"A"];NSString *str2 = [d4 objectForKey:@"A"];NSLog(@"str1 = %@",str1);NSLog(@"str2 = %@",str2);

打印结果：

str1 = chengdu

str2 = chengdu

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三、NSDictionary遍历方法

1、增强for循环方法

NSDictionary *d5 = @{                             @"A":@"zhengzhou",@"C":@"luoyang",@"H":@"jiaozuo"                             };        //第一步：获取所有的key        //第二步：根据key获取value值        for (NSString *key in d5) {            NSLog(@"key = %@,value = %@",key,[d5 valueForKey:key]);        }

打印结果：

key = A,value = zhengzhou

key = C,value = luoyang

key = H,value = jiaozuo

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2、block方法

[d5 enumerateKeysAndObjectsUsingBlock:^(id  _Nonnull key, id  _Nonnull obj, BOOL * _Nonnull stop) {NSLog(@"key = %@,value = %@",key,obj);        }];

打印结果：

key = A,value = zhengzhou

key = C,value = luoyang

key = H,value = jiaozuo

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三、NSDictionary的文件操作

1、把字典保存到文件中

//简写形式定义一个字典NSDictionary *d1 = @{                                 @"jz":@"jiaozuo",@"ly":@"luoyang",@"zz":@"zhengzhou"                                 };NSLog(@"d1 = %@",d1);//简写形式获取key对应的value值NSLog(@"%@",d1[@"jz"]);//把字典保存到文件中if([d1 writeToFile:@"/Users/leikai/Desktop/d1.plist" atomically:YES]){            NSLog(@"写入成功");            }else{            NSLog(@"写入失败");            }

打印结果：

d1 = {
jz = jiaozuo;
ly = luoyang;
zz = zhengzhou;
}

jiaozuo

写入成功

写入结果：

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2、从文件中读取字典

NSDictionary *d2 = [NSDictionary dictionaryWithContentsOfFile:@"/Users/leikai/Desktop/d1.plist"];NSLog(@"d2 = %@",d2);

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3、字典包含数组并读写操作

1）写入操作

NSArray *hnArr = @[@"zhengzhou",@"luoyang",@"jiaozuo"];NSArray *scArr = @[@"chengdu",@"dazhou"];NSDictionary *d3 = @{                                 @"hn":hnArr,@"sc":scArr                                 };if ([d3 writeToFile:@"/Users/leikai/Desktop/d3.plist" atomically:YES]) {            NSLog(@"写入成功");            }else{            NSLog(@"写入失败");            }

打印结果：

写入成功

写入结果：

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2）读取操作

NSDictionary *d5 = [NSDictionary dictionaryWithContentsOfFile:@"/Users/leikai/Desktop/d3.plist"];NSLog(@"d5 = %@",d5);//遍历[d5 enumerateKeysAndObjectsUsingBlock:^(id  _Nonnull key, id  _Nonnull obj, BOOL * _Nonnull stop) {//获取每个元素for (NSString *str in obj) {               NSLog(@"%@",str);                }            }];//获取每个数组NSArray *hnArr =  d5[@"hn"];NSLog(@"hnArr = %@",hnArr);NSArray *scArr = d5[@"sc"];NSLog(@"scArr = %@",scArr);

打印结果：

d5 = {
hn = (
zhengzhou,
luoyang,
jiaozuo
);
sc = (
chengdu,
dazhou
);
}

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zhengzhou
luoyang
jiaozuo
chengdu
dazhou

---

hnArr = (
zhengzhou,
luoyang,
jiaozuo
)

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scArr = (
chengdu,
dazhou
)