title: issue sharing links with Facebook iOs SDK 4.0 - FBSDKShareKit
body: <p>I'm having an annoying issue with the new FBSDshareKit (iOs SDK 4.0), i'm trying to share a link through the new api, as described in the new documentation. </p>
  
  <p>Once the native app is shown (using FBSDKShareDialogModeAutomatic) the link preview appears to be fine, showing title, image and description as seted, but after doing the actual post, there is no description, title or image, is shown the info rendered from the page (an appsFlyer link).</p>
  
  <p>Moreover, when I change the dialogue mode to FBSDKShareDialogModeShareSheet, no preview is shown (no image and no pre-fill), I'm aware about the new policy about pre-filling the content users share, but what about the thumbnail, title or description?</p>
  
  <p>The only option to seem working as expected is in safari or a web dialog, but this will prompt a new user login which is not a good ux experience.</p>
  
  <p>I guess sharing a link who has the respective og tags in it will work with all the mode options, but what happens if my app is just mobile and I want to share a link to the app store or appsflyer (as in my case) and not to a web version?</p>
  
  <p>I want to share custom info based on user info (like a promocode), not an static info, so, how is supposed to achieve that?</p>
  
  <p>Automatic mode code:</p>
  
  <pre><code>FBSDKShareLinkContent *shareContent = [[FBSDKShareLinkContent alloc] init];
  [shareContent setContentURL:[NSURL URLWithString:params.link]];
  [shareContent setContentTitle:params.title];
  [shareContent setContentDescription:params.description];
  [shareContent setImageURL:[NSURL URLWithString:params.picture]];
  
  [FBSDKShareDialog showFromViewController:[self presentingController]
                               withContent:shareContent
                                  delegate:self];
  </code></pre>
  
  <p>Forcing FBSDKShareDialogModeShareSheet:</p>
  
  <pre><code>FBSDKShareLinkContent *shareContent = [[FBSDKShareLinkContent alloc] init];
  [shareContent setContentURL:[NSURL URLWithString:params.link]];
  [shareContent setContentTitle:params.title];
  [shareContent setContentDescription:params.description];
  [shareContent setImageURL:[NSURL URLWithString:params.picture]];
  
  FBSDKShareDialog *dialog = [[FBSDKShareDialog alloc] init];
  dialog.mode = FBSDKShareDialogModeShareSheet;
  dialog.fromViewController = [self presentingController];
  dialog.shareContent = shareContent;
  dialog.delegate = self;
  [dialog show];
  </code></pre>
  
  <p>Do anyone have an advice about this?</p>