Raising an error from a ECL provider

Question

I extended Bart's Flickr ECL provider to thow an Exception() when it cannot access the third party Flickr API. This shows a nice error message in the Tridion 2013 CME GUI (see screenshot below).

Is throwing an new Exception() the best way to present an error to the user? and is there any other way to present a warning without failing?

throw new Exception(
    String.Format("Error while retrieving from Flickr; Error code {0}: {1}",
        error.AttributeValueOrDefault("code"),
        error.AttributeValueOrDefault("msg")));

Answer 1

There is no method build into ECL - the Tridion UI doesn't really have anything ECL could build it on top of as far as I know. An Anguilla data extender can't return a result and a warning. It can return a result or an error.

Try to avoid throwing exceptions in IContentLibrary.CreateContext. Unless you need to determine if the specific user has access to the remote server you should typically not even make any calls to the remote server here - it will slow down the UI when expanding publication nodes.

One workaround that can give some visual indication of an error without opening the error dialog would be to inject a node in the tree giving some visual feedback. So when the user expands the mountpoint node (ECL will call IContentLibraryContext.GetFolderContent), she will get a node with an error icon and for example the title "Unable to connect to the server". Any other operation (including calls to GetFolderContent for any other folder than the mountpoint folder) should throw the standard exception. To avoid someone managing to add this error node as an image somewhere I recommend using a folder item.

Answer 2

Additionally to Lars's answer, raising an error can indeed simply be done by throw new Exception(), there are no custom exceptions available in the ECL API that you can use.

I would use the override Exception(message, innerException) if you have an Exception available, and for the message you could use a resource, like I have done here in the class implementing the IContentLibrary interface:

public void Initialize(string mountPointId, string configurationXmlElement, IHostServices hostServices)
{
    try
    {
        // do something to initialize your provider 
        // like reading the mountpoint configuration
    }
    catch (Exception e)
    {
        // just raise the error with a readable message
        throw new Exception(string.Format(Resources.ConfigurationError, mountPointId), e);
    }
}

But as Lars mentions, I have to agree it would probably be nicer to do this check in your class which implements the IContentLibraryContext interface.

But keep in mind, while it is nice to show a visual indication to a user that the connection cannot be made for some reason, not everything has a use for this visual representation. When the publisher is trying to render an ECL item, it needs an error to halt the publishing process.