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How can I intercept the result of openDocument before NSDocument loads?

I am writing a program which will load and process XML data. If the XML file contains a single XML 'Dictionary' then it will need to open an NSDocument window (so far, so good - I can do this!), but if the XML file contains an array of Dictionaries then it should open up a list window, from which the individual Dictionaries can be opened into an NSDocument.

Because File->Open sends an action to First Responder->openDocument before the document window opens, I think that the openDocument function is not part of NSDocument. I'd like, therefore, to be able to intercept the open function before it hands off to NSDocument - just to check if the document is one that I want to be opening as a document rather than as my natty list view.

If, on the other hand, openDocument is an NSDocument function, how can I quietly close the NSDocument window and hand the XML list to my list window without raising an error in this one scenario? Of course, I don't want to suppress errors altogether - because there may be legitimate reasons to raise an error (unreadable file, bad syntax etc)

I realise that what I'm trying to do is a little unorthodox - but hopefully its possible. Any ideas?

Solution

  • openDocument: is an instance method of NSDocumentController.

    https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ApplicationKit/Classes/NSDocumentController_Class/Reference/Reference.html#//apple_ref/doc/uid/20000030-openDocument_

    You can subclass the NSDocumentController with your own. This will allow you to intercept openDocument:.

    If you want to check the file before creating a document, you'll need to use NSOpenPanel for the open file dialog. Then call openDocumentWithContentsOfURL:display:completionHandler: when you want to create the document. If you don't want to create the document, you can trigger whatever you want to do instead.