OC——Foundation—常用的类（3）----NSDictionary

NSDictionary

通过唯一的key找到对应的value，相当于java中的map

常见的创建NSDictionary的方法

//第一种创建方法，字典是不可变的，初始化之后不可添加删除元素

NSDictionary *dict=[NSDictionary dictionaryWithObject:@“v1”forKey:@“k1”];

 //第二种创建方法，最常用

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
                               @“v1”,@“k1”,
                               @“v2”,@“k2”,
                               @“v3”,@“k3”,
                               @“v4”,@“k4”,nil];

//第三种创建方法

 NSArray *values=[NSArray arrayWithObjects:@“v1”,@“v2”,@“v3”,@“v4”,nil]; NSArray *keys=[NSArray arrayWithObjects:@“k1”,@“k2”,@“k3”,@“k4”,nil]; NSDictionary *dict=[NSDictionary dictionaryWithObjects:values forKeys:keys]; 

字典使用：

快速遍历：for（NSString *key in dict）

使用迭代器遍历字典：

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
                               @“v1”,@“k1”,
                               @“v2”,@“k2”,
                               @“v3”,@“k3”,
                               @“v4”,@“k4”,nil];
//获取迭代器
NSEnumerator *enumerator=[dict keyEnumerator];
id key =nil
while(key=[enumerator nextObject]){
    id value=[dict objectForKey:key];
}

使用block遍历字典：

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
                               @“v1”,@“k1”,
                               @“v2”,@“k2”,
                               @“v3”,@“k3”,
                               @“v4”,@“k4”,nil];
//使用block
[dict enumerateKeysAndObjectsUsingBlock:^(id key,id value,BOOL *stop){
      NSLog(@“%@%@“,key,value);
}

NSDictionary的key排序

• -(NSArray *)keysSortedByValueUsingComparator:(NSComparator)cmptr
• -(NSArray *)keysSortedByValueWithOptions:(NSSortOptions)opts usingComparator:(NSComparator)cmptr
• -(NSArray *)keysSortedByValueUsingSelector:(SEL)comparator

用法参照NSArray的排序

NSMutableDictionary(可变字典）

//创建一个空的字典
NSMutableDictionary *dict=[NSMutableDictionary dictionary];

//创建两个字符串对象
NSString *str1=[NSString stringWithString:@“stu.gx203.1”];
NSString *str2=[NSString stringWithString:@“stu.gx203.2”];

//将字符串对象添加到可变字典中
[dict addObject:str1 forKey:@“k1”];
[dict addObject:str2 forKey:@“k2”];

添加其他字典到当前字典

NSDictionary *otherdict=[NSDictionary dictionaryWithObject:@“str.gx203.3” forKey:@“k3”];

[dict addEntriesFromDictionary:otherdict];

添加删除操作参考NSMutableArray