NSString *timestr = @"2016-07-11 08:34:22";
NSCharacterSet *doNotWant = [NSCharacterSet characterSetWithCharactersInString:@"-:"];
NSString *tempString = [[timestr componentsSeparatedByCharactersInSet: doNotWant]componentsJoinedByString:@""];
//tempString 最后的值：20160711083422
