NSDictionary和NSMutableDictionary

1.字典中的元素是以键值对的形式存储，在键值对中键和值都可以是任何对象，但是键往往是字符串，在字典中存储的对象没有顺序，更改键值对的添加顺序对最后的输出结果没有任何影响。

2.声明一个字典

NSDictionary * dict = [[[NSDictionary alloc] initWithObjectsAndKeys:@"One",@"1",@"three",@"3",@"two",@"2", nil]autorelease];  
NSLog(@"新生成的dictionary是：%@",dict);

3.Dictionary 的遍历

    3.1.枚举器法遍历dictionary，取值的时候是按照存储的顺序进行遍历的.可以分别遍历键和值

        3.1.1.遍历键

NSEnumerator * enumerator = [dict keyEnumerator];
id objKey;
while (objKey = [enumerator nextObject]) {
     NSLog(@"key is :%@",objKey);
}

        3.1.2.遍历值

NSEnumerator * enumerator = [dict objectEnumerator];
id objKey;
while (objKey = [enumerator nextObject]) {
     NSLog(@"key is :%@",objKey);
}

    3.2.foreach循环遍历dictionary的键

for(id objkey1 in dict){
    NSLog(@"foreach遍历dictionary 取出来的键是：%@",objkey1);
    //根据键取得dictionary中的值
    NSString * value = [dict objectForKey:objkey1];
    NSLog(@"根据键取出来的值是：%@",value);
}

4.向键值对中添加键和值

NSMutableDictionary * mutableDictionary = [[[NSMutableDictionary alloc] init] autorelease];
[mutableDictionary setObject:@"hello" forKey:@"A"];
[mutableDictionary setObject:@"world" forKey:@"B"];
[mutableDictionary setObject:@"I" forKey:@"C"];
[mutableDictionary setObject:@"love" forKey:@"D"];
[mutableDictionary setObject:@"you" forKey:@"E"];
        
NSLog(@"mutableDictionary is %@",mutableDictionary);

5.删除键值对 可以根据remove系列方法进行删除

[mutableDictionary removeObjectForKey:@"A"];
NSLog(@"删除后的字符串 mutableDictionary is %@",mutableDictionary);