Objective-C NSURL URLWithString在使用变量时似乎失败

NSString *urlString = @"http://www.example.com/path with spaces";
NSString *encodedUrlString = [urlString stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
NSURL *url = [NSURL URLWithString:encodedUrlString];

NSURLComponents *components = [[NSURLComponents alloc] init];
[components setScheme:@"http"];
[components setHost:@"www.example.com"];
[components setPath:@"/path"];

NSArray *queryItems = @[[NSURLQueryItem queryItemWithName:@"param1" value:@"value1"],
                        [NSURLQueryItem queryItemWithName:@"param2" value:@"value2"]];
[components setQueryItems:queryItems];

NSURL *url = [components URL];