OC-NSDictionary

字典

分类:不可变和可变字典

元素类型:id（即:任意的对象指针）

特点:字典是无序的

内容:键值对:key -->value;键值对必须成对出现,key一般是NSString*类型，方便操作

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1)创建一个不可变字典:

方法一:

NSDictionary * dict = [[NSDictionaryalloc]initWithObjectsAndKeys:@"one",@"1",@"tow",@"2",@"three",@"3",@"four",@"4",@"five",@"5",@"ten",@"10",nil];

方法二:

NSDictionary * dict2 = [NSDictionarydictionaryWithDictionary:dict];

方法三:

NSArray * keys = [[NSArrayalloc]initWithObjects:@"1",@"2",@"3",nil];

NSArray * values = [[NSArrayalloc]initWithObjects:@"one",@"two",@"three",nil];

NSDictionary * dict3 = [[NSDictionaryalloc]initWithObjects:values forKeys:keys];

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2)遍历字典:

说明:a.字典的查找效率要比数组快

         b.哈希   

方法一:

//创建一个key的枚举器

NSEnumerator * enumer1 = [dict3keyEnumerator];

id key;

//遍历字典

while (key = [enumer1nextObject])

{

   NSLog(@"value = %@",[dict3 objectForKey:key]);

}

        

方法二:

//快速枚举,枚举的是key

for (id keyin dict3) 

{

    NSLog(@"key = %@ , value = %@",key,[dict3objectForKey:key]);

}

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3)获取键值对个数

例子:

NSLog(@"count = %ld",[dict3count]);//键值对的个数

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4)字典的最主要功能:根据key找到对应值

例子:

NSLog(@"%@",[dict3objectForKey:@"three"]);

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5)创建可变字典:

例子:

NSMutableDictionary * dict = [[NSMutableDictionaryalloc]initWithObjectsAndKeys:@"1",@"one",@"2",@"two",@"3",@"three",nil];

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6)对可变字典的操作:

----------增------------

[dictsetObject:@"4"forKey:@"four"];//增加键值对

----------删------------

[dictremoveObjectForKey:@"one"];//删除键值对

[dictremoveAllObjects];//删除所有的键值对

----------改------------

[dictsetObject:@"yi"forKey:@"one"];//如果字典中这个key存在那么setObject: forKey:代表的是修改、、如果key不存在那么代表的增加