Yes, it’s free code time again. I’ve been neglecting the blog for some time so hopefully this will make up for it. Think of it as that conciliatory heart-shaped box of chocolates used as a sorry way to make up for forgetting about your birthday, after which, I go back to my old ways of sitting on the couch all day watching sports, ignoring you.

In version 2.2 of Hazel, I added mini AppleScript and shell script editors so that people could enter scripts inline without having to go to another program and saving it to an external file. I’ll admit, I didn’t set out to make an uber-editor since it was intended for small scripts. Nonetheless, a user recently pointed out that when a line wraps, it’s hard to tell if it’s a continuation of the previous line or a new one. One of his suggestions was putting line numbers in the left gutter. If you don’t know what I’m talking about, look at TextMate (the example he cited) or XCode (you need to turn it on in preferences). I thought it might be overkill for a script editor that will mostly be used for scripts less than ten lines long. I’m instead considering doing an indented margin for continuation lines. Less visual clutter and addresses the problem at hand.

Nonetheless, I was curious about implementing line numbers. Poking around, I found some tips on how to do it but it seemed like there were odd problems implying it wasn’t as straightforward as one would think. So, snatching some free time in between other things, I decided to tackle the problem.

I looked into subclassing NSRulerView. The problem is that NSRulerView assumes a linear and regular scale. Now, to make it clear, I am talking about numbering logical lines, not visual ones. If a line wraps, it still counts as one line even if it takes two or more visually. The scale is solely dependent on the layout of the text and can’t be computed from an equation. Despite these limitations, I went ahead and subclassed NSRulerView. If anything, NSScrollView knows how to tile it.

I had this notion that NSRulerView was a view that synced its dimensions with the document view of the scrollview. With a vertical ruler, I assumed it would be as tall as the document and the scroll view just scrolls it in tandem with the document. Not so. It’s only as tall as the scrollview. That means you have to translate the scale depending on the clipview’s bounds.

I added some marker support via an NSRulerMarker subclass that knows about line numbers. The line number view will draw the markers underneath the labels a la XCode (with the text inversed to white). The sample project uses another subclass which will toggle markers on mouse click. While NSRulerView usually delegates this to its client view it made more sense to just do it in a subclass of NSRulerView. You have to subclass something to get it to work and it made more sense to subclass the ruler view since the code to handle markers never interacts with anything in the client view anyways. Personally, I find it an odd design on Apple’s part and would have preferred a regular delegate.

The project is linked below. The main classes are NoodleLineNumberView and NoodleLineNumberMarker. Some notes:

To integrate: just create the line number view and set it as the vertical ruler. Make sure the document view of the scrollview is an NSTextView or subclass. Depending on the order of operations, you may have to set the client view of the ruler to the text view.

The view will expand it’s width to accommodate the widths of the labels as needed.

The included subclass (MarkerLineNumberView) shows how to deal with markers. It also shows how to use an NSCustomImageRep to do the drawing. This allows you to reset the size of the image and have the drawing adjust as needed (this happens if the line number view changes width because the line numbers gained an extra digit).

Note that markers are tied to numerical lines, not semantic ones. So, if you have a marker at line 50 and insert a new line at line 49, the marker will not shift to line 51 to point at the same line of text but will stay at line 50 pointing at whatever text is there now. Contrast with XCode where the markers move with insertions and deletions of lines (at least as best as it can). This is logic that you’ll have to supply yourself.

More details, including performance notes, can be found in the Read Me file included in the project.

I’m putting this out there because I’m probably not going to use it and it seems like a waste of some useful code. Also, my apologies to the user who asked for this feature. I feel like somewhat of a jerk going through the trouble of implementing the feature and not including it. It was more of a fun exercise on my part but I still feel it’s not suitable for Hazel. That said, I may consider adding it and having it available via a hidden default setting. Votes for or against are welcome.

In the meantime, you can use the code however you want. MIT license applies. Please send me any bug reports, suggestions and feedback.

Enjoy.

Download Line View Test.zip (version 0.4.1)

Update (Oct. 6, 2008): Uploaded version 0.3. Fixes bugs found by Jonathan Mitchell (see comments on this post). Also made line calculations lazy for better performance.

Update (Oct. 10, 2008): Uploaded version 0.4. Fixes bugs mentioned in the comments as well as adds methods to set different colors. There is a display bug that happens when linking against/running on 10.4. See the Read Me for details.

Update (Oct. 13, 2008): Uploaded version 0.4.1. Figured out the 10.4 display bug. Apparently, NSRulerView’s setRuleThickness: method doesn’t like non-integral values. Rounding up solves the problem. Thanks to this page for identifying the problem.

Update (Sep. 29, 2009): I have included this class in my NoodleKit repository so you should check there for future updates.