1. 创建NSMutableDictionary
    NSMutableDictionary *mDict = [NSMutableDictionary dictionary];   //创建一个空字典
    NSMutableDictionary *mDict = [NSMutableDictionary dictionaryWithCapacity:3];//创建一个容量为3的字典

2. 给字典添加键值对
   [mDict setValue:@"value1" forKey:@"key1"];
   [mDict setValue:@"value2" forKey:@"key2"];
注意：键值（key）不可以重复

3. 快速创建NSMutableDictionary
   NSMutableDictionary *mDict = [NSMutableDictionary dictionary];
   mDict.dictionary = @{@"key1":@"value1",@"key2":@"value2"};

3. 删除字典内容
   [mDict removeObjectForKey:@"key1"];    //删除键值为key1的键值对
   [mDict removeAllObjects];                        //删除所有键值对

4. 修改value
   [mDict setObject:@"value3" forKey:@"key1"];   //注意区分setValue和setObject
   mDict[@"key1"] = @"value4";

5. 遍历dictionary
   NSArray *array = [mDict allKeys];   //获取所有键值
   //根据所有键值来遍历dictionary

1. 创建NSMutableDictionary
    NSMutableDictionary *mDict = [NSMutableDictionary dictionary];   //创建一个空字典
    NSMutableDictionary *mDict = [NSMutableDictionary dictionaryWithCapacity:3];//创建一个容量为3的字典

2. 给字典添加键值对
   [mDict setValue:@"value1" forKey:@"key1"];
   [mDict setValue:@"value2" forKey:@"key2"];
注意：键值（key）不可以重复

3. 快速创建NSMutableDictionary
   NSMutableDictionary *mDict = [NSMutableDictionary dictionary];
   mDict.dictionary = @{@"key1":@"value1",@"key2":@"value2"};

3. 删除字典内容
   [mDict removeObjectForKey:@"key1"];    //删除键值为key1的键值对
   [mDict removeAllObjects];                        //删除所有键值对

4. 修改value
   [mDict setObject:@"value3" forKey:@"key1"];   //注意区分setValue和setObject
   mDict[@"key1"] = @"value4";

5. 遍历dictionary
   NSArray *array = [mDict allKeys];   //获取所有键值
   //根据所有键值来遍历dictionary