Prevent NSDocument's auto-saving while its content is editing

Question

I develop a document-based Cocoa application allowed saving documents asynchronous. Namely, my NSDocument subclass returns ture on canAsynchronouslyWrite(to:typeOf:for:).

I want dynamically and silently delay (or cancel) regular auto-saving if the document content is editing. At first, I thought it's enough when I throw an error in checkAutosavingSafety(), but it displays an error message dialog for user.

I believe there is a standard way for such a standard demand. But I'm not sure either where in a NSDocument subclass I should prevent saving and to which method I should say "please wait".

Does someone have any idea for this?

For the reference, the content of document is text which is managed by NSTextView subclass.

Don't throw an error in `checkAutosavingSafety` and return false? — Willeke, May 24 '17 at 20:18
@Willeke Because I write the code in Swift, there is no way just to return false. — 1024jp, May 24 '17 at 22:43
Maybe, throwing a specific error can solve my problem. But then, I need to know which error I should throw. — 1024jp, May 24 '17 at 23:04

score 0 · Accepted Answer · answered Feb 17 '18 at 06:56

I finally found that throwing an .userCalcelled error in a saving process with autosavingIsImplicitlyCancellable can cancel autosaving.

/// make autosaving cancellable
override var autosavingIsImplicitlyCancellable: Bool {

    return true
}


/// save or autosave the document contents
override func save(to url: URL, ofType typeName: String, for saveOperation: NSDocument.SaveOperationType, completionHandler: @escaping (Error?) -> Void) {

    // cancel if something is working
    guard saveOperation != .autosaveInPlaceOperation || !self.isEditing else {
        completionHandler(CocoaError(.userCancelled))
        return
    }

    super.save(to: newUrl, ofType: typeName, for: saveOperation, completionHandler: completionHandler)
}


/// whether your document is currently being edited
var isEditing: Bool {

    // check your document state
}

Prevent NSDocument's auto-saving while its content is editing

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