Flickr API 返回的场值无效

Question

I have this app that searches tags on flickr and returns results.

The results are displayed on an infinite collection view.

Results are returned 100 at a time.

I start to scroll and reach the bottom of the scroll view. Another 100 elements are requested from Flickr and the thing works fine.

If I continue to scroll down for a while, after entering the 5th page (elements 400-499), I start to get this error:

NSURLErrorRelatedURLSessionTaskErrorKey=(
    "LocalDataTask <D87E6C4C-B8CB-46D1-B891-3E7CDF35ABDF>.<1>"
), NSLocalizedDescription=A server with the specified hostname could not be found., NSErrorFailingURLStringKey=https://farm0.static.flickr.com/0/50255650726_a4c7ba2298.jpg, NSErrorFailingURLKey=https://farm0.static.flickr.com/0/50255650726_a4c7ba2298.jpg, _kCFStreamErrorDomainKey=12}

Look at the url.

https://farm0.static.flickr.com/0/50255650726_a4c7ba2298.jpg

if you change farm0 to farm1 the image loads.

I am creating the image download url like this:

func makeDownloadURL() -> URL{
  let path = "https://farm\(farm).static.flickr.com/\(server)/\(id)_\(secret).jpg"
  return URL(string: path)!
}

The strange part is that if I continue to scroll past the missing images, at some point, valid images start to fill the collection view. Then, the problem again, valid images again, and so one.

I am using this to build the search URL

  func makeSearchURLComponents(searchString:String) -> URLComponents? {
    var components = URLComponents()
    components.scheme = "https"
    components.host = "api.flickr.com"
    components.path = "/services/rest"

    let queryMethod       = URLQueryItem(name: "method", value: "flickr.photos.search")
    let queryAPI          = URLQueryItem(name: "api_key", value: flickrAPI)
    let queryFormat       = URLQueryItem(name: "format", value: retrieveFormat)
    let querySafeSearch   = URLQueryItem(name: "safe_search", value: SafeSearch.Safe.rawValue)
    let querySearchString = URLQueryItem(name: "tags", value: searchString)
    let queryPageNumber   = URLQueryItem(name: "page", value: String(pageNumber))
    let querycallBack     = URLQueryItem(name: "nojsoncallback", value: "1")
    components.queryItems = [queryMethod, queryAPI, queryFormat, querySafeSearch, querySearchString, queryPageNumber, querycallBack]

    return components
  }

why is that.

Answer 1

It appears to be a flickr problem.

The solution is to correct farm to 1 when it is zero.

let correctedFarm = farm == 0 ? 1 : farm

It is a hack to circumvent their bug.