Xcode Trick - Shortcut to duplicate a line of code

10 May 2010

One feature I miss in Xcode is the ability to duplicate a line of text with a simple two-key combo. Sure, I could select the line and then copy and paste, but it’s far too fiddly. For example, let’s say I wanted to add another line to this array:

I would have to type:

+ move to start of line

+ (shift-down) select line

+ C (copy)

(down) (deselect)

+ V (paste)

And I would end up with this.

That’s far too much work.

Digging through Xcode’s preferences I couldn’t find anything that would help, but then I stumbled on a page called Customizing the Cocoa Text System that showed me how this could work.

So, I created a directory:

mkdir ~/Library/KeyBindings

And created the file: ~/Library/KeyBindings/DefaultKeyBinding.dict

    "^d" = ("moveToEndOfLine:",
        "deleteToBeginningOfLine:", // line in kill buffer
        "yank:", // put back what was deleted
        "yank:"); // duplicate line  

Restarted Xcode, and now a ^d (control d) duplicates the line. And I can easily add the new element to the array.

If you want to experiment with your own tweaks, there is a list of all selectors. You’ll need to restart Xcode after each change to test your changes. I ran into a small problem with Xcode doing auto-intent after i added a newline with insertNewline:. Luckily, insertLineBreak has the same effect, but avoids the problem of extra whitespace getting added on the duplicated line.

If you prefer to download the file: http://xinsight.ca/blog/files/DefaultKeyBinding.dict.txt

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