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Re: How to enforce a single NSDocument ... or should I do something else?
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Re: How to enforce a single NSDocument ... or should I do something else?


  • Subject: Re: How to enforce a single NSDocument ... or should I do something else?
  • From: Mike Abdullah <email@hidden>
  • Date: Tue, 5 Jan 2010 19:02:05 +0000

On 5 Jan 2010, at 17:34, Martin Stanley wrote:

> Thanks for the very quick response!
>
> I don't quite understand step 2:  how do I decide what to return from -openDocumentWithContentsOfURL:  if the callback hasn't been called yet and therefore I don't know if the user cancelled the close of the first document?

I mean to say that either approach should work. But I haven't tried them, so keep your options open.
>
> I think the basic problem for me is that  -canCloseDocument… does not block.

Well it can't block, because the sheet needs to be interacted with.
>
> Martin
>
>
> On 2010-01-05, at 12:10 PM, Mike Abdullah wrote:
>
>> Override -openDocumentWithContentsOfURL:
>>
>> 1. If you've already got a document open, send -canCloseDocument… to the open document, supplying the callback info
>>
>> 2. Either:
>> 	A) Return nil and an NSUserCancelled error.
>> 	B) Return the existing document.
>>
>> 3. When you get the callback from -canCloseDocument… call super's implementation of -openDocumentWithContentsOfURL:
>>
>> On 5 Jan 2010, at 16:45, Martin Stanley wrote:
>>
>>> I have a Core-Date application that uses the Cocoa Document architecture (NSPersistentDocument) and would like to ensure that the user only can have 1 document open at a time. Think of this application as similar to Mail.app or Addressbook.app, etc. except that I would like the user to be able to open different persistent stores at will, just not simultaneously.
>>>
>>> (As an aside, the reason for this is because my document has many related windows and I think it would be confusing for the user. It would not be obvious which auxiliary window relates  to which document. I may fix this in the future by using the concept of Inspectors, but at this point I'm not sure if this is the correct model.)
>>>
>>> I searched extensively and came up with the recommendation that I subclass NSDocumentController and override:
>>> 	- (id)openDocumentWithContentsOfURL:display:error:
>>> This was recommended over simply trapping the open menu item(s).
>>>
>>>
>>> This seemed very promising until I ran into a stumbling block. In openDocumentWithContentsOfURL:display:error: I check to see if there is an already open document and if so call:
>>> 	canCloseDocumentWithDelegate:shouldCloseSelector:contextInfo:
>>> with an appropriate delegate and selector. The problem is that this returns immediately, even in the case when the document is dirty and it presents a modal dialog to the user. Because of this, the 2nd document is opened before I have a chance to deal with the first one.
>>>
>>> All of this is making me wonder if I'm taking the wrong approach.
>>>
>>> Should I figure out a way to prevent the 2nd document from opening before the first one is either saved or abandoned: (override canCloseDocumentWithDelegate:shouldCloseSelector:contextInfo: in my NSPersistentDocument subclass)? This feels like the solution is getting uglier by the minute.
>>>
>>> Or is there a much easier way to accomplish what I want to do? Or should I be looking at a entirely different approach for my application?
>>>
>>> Thanks,
>>> Martin
>>>
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References: 
 >How to enforce a single NSDocument ... or should I do something else? (From: Martin Stanley <email@hidden>)
 >Re: How to enforce a single NSDocument ... or should I do something else? (From: Mike Abdullah <email@hidden>)
 >Re: How to enforce a single NSDocument ... or should I do something else? (From: Martin Stanley <email@hidden>)

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