enumerateKeysAndObjectsUsingBloc

for in遍历字典时只能先得到value ，再通过value取对应的key
enumerateKeysAndObjectsUsingBlock 可以同时遍历出key和value
通过value取key的方法

- (void)setEnumDictionary
{
NSDictionary *dic = [NSDictionary dictionary];
dic = @{
        @"1":@"a",
        @"2":@"b",
        @"3":@"c",
        @"4":@"d",
        @"5":@"e",
        @"6":@"f",
        @"7":@"g",
        @"8":@"h",
        @"9":@"i",
        @"10":@"j",
        @"11":@"k",
        @"12":@"L",
        };

[dic enumerateKeysAndObjectsUsingBlock:^(id  _Nonnull key, id  _Nonnull obj, BOOL * _Nonnull stop) {
    if ([@"d" isEqualToString:obj]) {
        NSLog(@" = %@",key);
        *stop = YES;
    }    
}];
}