//遍历
//1.先找到所有key；
//2.计算key的个数，用于循环
//3.通过key的数组，找到key对应的value
NSArray *keyss=[nulldic allKeys];
NSInteger count=[keyss count];
for (int i=0; i<count; i++) {
id key=[keyss objectAtIndex:i];
NSLog(@"%@",[nulldic objectForKey:key]);
}
//快速枚举（遍历）
for(id key in nulldic){
id obj=[nulldic objectForKey:key];
NSLog(@"%@",obj);
}
//枚举对象
//1.将字典里所有的key转成枚举对象用于遍历
NSEnumerator *keyEnum=[nulldic keyEnumerator];
id key=[keyEnum nextObject];
while (key) {
id obj=[nulldic objectForKey:key];
NSLog(@"%@",obj);
key=[keyEnum nextObject];
}