Discussion:
Implementing an import command in NSDocument-based app
(too old to reply)
Rick Mann
2018-05-16 07:26:47 UTC
Permalink
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
***@latencyzero.com


_______________________________________________

Cocoa-dev mailing list (Cocoa-***@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/gegs%40ml-in.narkive.net

This email sent to ***@ml-in.narkive.net
Pascal Bourguignon
2018-05-16 07:55:36 UTC
Permalink
Post by 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?
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__




_______________________________________________

Cocoa-dev mailing list (Cocoa-***@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/gegs%40ml-in.narkive.net

This email sent to ***@ml-in.narkive.net
Alastair Houghton
2018-05-16 09:32:44 UTC
Permalink
Post by Pascal Bourguignon
Post by 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.
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).
Post by Pascal Bourguignon
- 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.
Post by Pascal Bourguignon
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.
Post by Pascal Bourguignon
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/<your app>/Unsaved Documents (or similar) instead.
Post by Pascal Bourguignon
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

_______________________________________________

Cocoa-dev mailing list (Cocoa-***@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/gegs%40ml-in.narkive.net

This email sent to geg
Rick Mann
2018-05-16 08:13:44 UTC
Permalink
Thank you, that's all good advice.
Post by 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
_______________________________________________
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
https://lists.apple.com/mailman/options/cocoa-dev/rmann%40latencyzero.com
--
Rick Mann
***@latencyzero.com


_______________________________________________

Cocoa-dev mailing list (Cocoa-***@lists.apple.com)

Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com

Help/Unsubscribe/Update your Subscription:
https://lists.apple.com/mailman/options/cocoa-dev/gegs%40ml-in.narkive.net

This email sent to ***@ml-in.narkive.net
Continue reading on narkive:
Loading...