NSTextStorageDelegate's textStorage(_,willProcessEditing:,range:,changeInLength:) moves selection

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I'm trying to implement a syntax-coloring text editor that also does things like insert whitespace at the start of a new line for you, or replace text with text attachments.

After perusing the docs again after a previous implementation had issues with undoing, it seems like the recommended bottleneck for this is NSTextStorageDelegate's textStorage(_,willProcessEditing:,range:,changeInLength:) method (which states that Delegates can change the characters or attributes., whereas didProcessEditing says I can only change attributes). This works fine, except that whenever I actually change attributes or text, the text insertion mark moves to the end of whatever range of text I modify (so if I change the style of the entire line, the cursor goes at the end of the line).

Does anybody know what additional call(s) I am missing that tell NSTextStorage/NSTextView not to screw up the insertion mark? Also, once I insert text, I might have to tell it to move the insertion mark to account for text I've inserted.

Note: I've seen Modifying NSTextStorage causes insertion point to move to the end of the line, but that assumes I'm subclassing NSTextStorage, so I can't use the solution there (and would rather not subclass NSTextStorage, as it's a semi-abstract subclass and I'd lose certain behaviours of Apple's class if I subclassed it).

nstextstorage nstextview swift3 syntax-highlighting macos
2 Answers

The above accepted answer with the notification center worked for me, but I had to include one more thing when editing text. (Which may be different from selection).

The editedRange of the NSTextStorage was whack after the notification center callback. So I keep track of the last known value myself by overriding the processEditing function and using that value later when I get the callback.

override func processEditing() {
        // Hack.. the editedRange property when reading from the notification center callback is weird
        lastEditedRange = editedRange
        super.processEditing()
    }
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