Re: Implementing an import command in NSDocument-based app

[Alastair Houghton]

On 16 May 2018, at 08:55, Pascal Bourguignon  wrote:

>> Le 16 mai 2018 à 09:26, Rick Mann  a écrit :
>> 
>> I'm working on a little NSDocument-based app. The documents are packages (a 
>> directory containing multiple files). One of the operations is to import a 
>> music file into the document, which should copy the music file into the 
>> package, and set it as the track for the document.
>> 
>> Undoing this operation is somewhat complex (where do I store the previous 
>> track if any?). So for now, I want to ignore undo.

The user’s temporary folder would be a good place to store the previous track 
(you probably want to delete it when the program terminates).

> You have a choice, for « unsaved » documents:
> - either you keep them only in memory, or
> - you record them in a « untitled » file package, perhaps in /tmp.

I wouldn’t recommend /tmp. The trouble with /tmp is that it’s global, not 
per-user, and so if you’re using that location you typically need to take steps 
to make a per-user subdirectory in order to keep others from tampering with the 
current user’s files; there are a lot of ways to get that wrong and end up with 
a security hole.

However, you can use NSFileManager’s 
-URLForDirectory:inDomain:appropriateForURL:create:error: method to obtain an 
appropriate per-user temporary folder that you can use instead.

> I guess you see where I’m drifting to: it’s best to keep your document saved 
> on disk all the time, even before it’s saved explicitely by the user.

Agreed.

>  The bonus feature, is that if your application crashes, or the system is 
> powered off, you can restore the unsaved document (if you don’t put it in 
> /tmp, but eg. in ~/Documents/Unsaved\ Documents/).

But please don’t create your own subfolders in the user’s Documents folder. The 
Documents folder belongs to the user — it isn’t yours to tinker with as you 
please, and I know I’m not alone in feeling a visceral hatred when I see that 
software has, without asking, created its own subfolders there. If you want 
somewhere to store these, I’d suggest putting them in ~/Library/Application 
Support//Unsaved Documents (or similar) instead.

>  Then you can copy the imported data to a file as soon as the import function 
> is activated, so even if the imported file is deleted, the imported data will 
> be there.  And then you don’t have to implement in-memory data structure for 
> unsaved documents, since by definition all documents are backed by files the 
> same way (only a different path), whether they’re « saved » nor not « saved 
> ».  Much simplier.  When you launch the application, scan the unsaved 
> documents folder for unsaved document,  and re-open them, to let the user 
> choose whether to close (and delete them), or to save them.

If you’re going to open them automatically, it is a very good idea to prompt 
the user first — i.e. let them know they have unsaved documents from a previous 
session and offer to open them. Why? Because if the thing that caused your 
application to terminate was a crash caused by some problem with the document 
structure, then auto-opening will likely cause your application to crash again 
— and that will be quite infuriating for the end user.

Kind regards,

Alastair.

--
http://alastairs-place.net

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Re: Implementing an import command in NSDocument-based app

[Rick Mann]

Thank you, that's all good advice.


> On May 16, 2018, at 00:26 , Rick Mann  wrote:
> 
> I'm working on a little NSDocument-based app. The documents are packages (a 
> directory containing multiple files). One of the operations is to import a 
> music file into the document, which should copy the music file into the 
> package, and set it as the track for the document.
> 
> Undoing this operation is somewhat complex (where do I store the previous 
> track if any?). So for now, I want to ignore undo.
> 
> But I'm not sure how to copy the track file into the package. For example, 
> what if it's an untitled document, and therefore has no package on disk? The 
> action should result in a dirty document that isn't committed to disk until 
> the next save (be it automatic or manual).
> 
> Can this even be done without undo?
> 
> Along those lines, how do I mark a document as dirty after some change, 
> without making the change undoable?
> 
> Thanks,
> 
> -- 
> Rick Mann
> rm...@latencyzero.com
> 
> 
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-- 
Rick Mann
rm...@latencyzero.com


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Re: Implementing an import command in NSDocument-based app

[Pascal Bourguignon]

> Le 16 mai 2018 à 09:26, Rick Mann  a écrit :
> 
> I'm working on a little NSDocument-based app. The documents are packages (a 
> directory containing multiple files). One of the operations is to import a 
> music file into the document, which should copy the music file into the 
> package, and set it as the track for the document.
> 
> Undoing this operation is somewhat complex (where do I store the previous 
> track if any?). So for now, I want to ignore undo.
> 
> But I'm not sure how to copy the track file into the package. For example, 
> what if it's an untitled document, and therefore has no package on disk? The 
> action should result in a dirty document that isn't committed to disk until 
> the next save (be it automatic or manual).
> 
> Can this even be done without undo?
> 
> Along those lines, how do I mark a document as dirty after some change, 
> without making the change undoable?

You have a choice, for « unsaved » documents:
- either you keep them only in memory, or
- you record them in a « untitled » file package, perhaps in /tmp.

An element of choice is how you want to process the import:
- either you copy the data immediately,
- or you copy the data only when the document is saved.

In the later case, you and the user will have a problem if the imported file is 
deleted before the unsaved document is saved.

If you copy the data immediately, when the unsaved document is only kept in 
memory, then it may be difficult to load big files in memory, notably if bigger 
than the actual RAM available: the system will start to swap the memory to the 
swap file, and this will be very slow, and may even crash if there’s not enough 
free space on the disk where the swap files are stored.  But one good news is 
that nowadays everybody has 64-bit systems, so it should be possible to load in 
memory even files bigger than 4GB.

I guess you see where I’m drifting to: it’s best to keep your document saved on 
disk all the time, even before it’s saved explicitely by the user.  The bonus 
feature, is that if your application crashes, or the system is powered off, you 
can restore the unsaved document (if you don’t put it in /tmp, but eg. in 
~/Documents/Unsaved\ Documents/).  Then you can copy the imported data to a 
file as soon as the import function is activated, so even if the imported file 
is deleted, the imported data will be there.  And then you don’t have to 
implement in-memory data structure for unsaved documents, since by definition 
all documents are backed by files the same way (only a different path), whether 
they’re « saved » nor not « saved ».  Much simplier.  When you launch the 
application, scan the unsaved documents folder for unsaved document,  and 
re-open them, to let the user choose whether to close (and delete them), or to 
save them.

-- 
__Pascal J. Bourguignon__




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Implementing an import command in NSDocument-based app

[Rick Mann]

I'm working on a little NSDocument-based app. The documents are packages (a 
directory containing multiple files). One of the operations is to import a 
music file into the document, which should copy the music file into the 
package, and set it as the track for the document.

Undoing this operation is somewhat complex (where do I store the previous track 
if any?). So for now, I want to ignore undo.

But I'm not sure how to copy the track file into the package. For example, what 
if it's an untitled document, and therefore has no package on disk? The action 
should result in a dirty document that isn't committed to disk until the next 
save (be it automatic or manual).

Can this even be done without undo?

Along those lines, how do I mark a document as dirty after some change, without 
making the change undoable?

Thanks,

-- 
Rick Mann
rm...@latencyzero.com


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