Foundaton框架-->NSDictionary字典

一、NSDictionary基本概念

• NSDictionary的作用类似：通过一个key，就能找到对应的Value

• NSDictionary是一个不可变的，一旦初始化后，就无法修改

二、NSDictionary的创建

• 方法一：
• 创建一个dictionaryWithObject
• 创建多个dictionaryWithObjects

NSDictionary *dict = [NSDictionary dictionaryWithObject:@"lm" forKey:@"name"];
NSString *name = [dict objectForKey:@"name"];

• 方法二：简单方法
• NSDictionary *dict = @{key1:value1,key2:value2};

NSDictionary *dict = @{@"lm":@"name",@"25":@"age",@"160":@"height"};

三、如何获取

• 方法一：objectForKey

NSString *name = [dict objectForKey:@"name"];

• 方法二：NSLog(@"%@", dict[@"name"]);

四、字典的遍历

• 如何获取字典中key和value的个数,

• 在字典中key称之为键, value称之为值

• NSLog(@"count = %lu", [dict count]);

• 方法一：for循环【不用】

 for (int i = 0; i < dict.count; ++i) {
        // 获取字典中所有的key
        NSArray *keys = [dict allKeys];
        // 取出当前位置对应的key
//        NSLog(@"%@", keys[i]);
        NSString *key = keys[i];
        NSString *value = dict[key];
        NSLog(@"key = %@, value = %@", key, value);
    }

• 方法二：forin遍历字典【不用】

for (NSString *key in dict) {
//        NSLog(@"%@", key);
        NSString *value = dict[key];
        NSLog(@"key = %@, value = %@", key, value);
    }

• 方法三：迭代器遍历enumerateKeysAndObjectsUsingBlock

    NSDictionary *dict = @{@"lm":@"name",@"25":@"age",@"160":@"height"};
    [dict enumerateKeysAndObjectsUsingBlock:^(id  _Nonnull key, id  _Nonnull obj, BOOL * _Nonnull stop) {
        NSLog(@"obj:%@, key:%@", obj, key);
    }];

五、字典文件读写

• 字典读取writeToFile
• 字典写入dictionaryWithContentsOfFile

[dict writeToFile:@"/Users/jeffrey/Desktop/php.plist" atomically:YES];
NSDictionary * dict = [NSDictionary dictionaryWithContentsOfFile:@"/Users/jeffrey/Desktop/php.plist"];

六、NSMutableDictionary

• 1.创建一个空的字典

NSMutableDictionary *dictM = [NSMutableDictionary  dictionary];
```objc
- 2.如何添加
```objc
[dictM setObject:@"lm" forKey:@"name"];
// 会将传入字典中所有的键值对取出来添加到dictM中
    [dictM setValuesForKeysWithDictionary:@{@"age":@"30", @"height":@"1.75"}]
```objc
- 3.如何获取
```objc
NSLog(@"%@", dictM[@"lm"]);

• 4.如何删除

[dictM removeObjectForKey:@"lm"];

• 5.如何修改
  • 如果利用setObject方法给同名的key赋值, 那么新值会覆盖旧值

[dictM setObject:@"88" forKey:@"age"];
     dictM[@"age"] = @"88";