objective-c基础语法之字典NSDIctionary、NSMutableDictionary

• 不可变字典NSDictionary的创建
  

  //创建一个空字典
  NSDictionary *dic = [[NSDictionary alloc]init];
  //根据本地文件创建一个字典
  NSDictionary *dic = [[NSDictionary alloc]initWithContentsOfFile:(NSString *)];
  //根据网址URL创建一个字典
  NSDictionary *dic = [[NSDictionary alloc]initWithContentsOfURL:(NSURL *)];
  //根据已知字典创建一个新的字典
  NSDictionary *dic = [[NSDictionary alloc]initWithDictionary:(NSDictionary *)];
  
  //根据值的集合数组与键的集合数组创建一个字典
  NSDictionary *dic = [[NSDictionary alloc]initWithObjects:(NSArray *) forKeys:(NSArray *)];
  //使用如下：
  NSArray *arr_values = [[NSArray alloc]initWithObjects:@"Mary","female", nil];
      NSArray *arr_keys = [[NSArray alloc]initWithObjects:@"name","sex", nil];
      NSDictionary *dic = [[NSDictionary alloc]initWithObjects:arr_values forKeys:arr_keys];

   
• 不可变字典与可变字典的创建方式不同的方法如下：
  

  //创建容量初始为多少的字典
  NSMutableDictionary *mutable_dic = [[NSMutableDictionary alloc]initWithCapacity:(NSUInteger)];
  //使用如下：

  NSMutableDictionary *mutable_dic = [[NSMutableDictionary alloc]initWithCapacity:0];

   
• 读取字典中的数据
  

  //读取字典中的值
  [mutable_dic objectForKey:(id)];
  //读取键为@"name"对应的值
  [mutable_dic objectForKey:@"name"];
  
  //获取字典的长度
  [mutable_dic count];
  
  //获取字典中所有的键值
  [mutable_dic allKeys];