Core Text Performance

Question

I am seeing some performance issues with Core Text when it is run on the original iPad.

I have created an editable view using Core Text and the UITextInput protocol which is based around OmniGroup's OUIEditableFrame.

When there is a fair amount of text in the view say 180 lines, typing/input lags greatly behind and one tap on a key usually takes 1-2 seconds.

Using instruments with the simulator I was able to narrow down the problem and find out what was taking so much time. Turns out it's because I redraw the frame with every key stroke, what takes up so much time is calling CTFramesetterCreateWithAttributedString and CTFramesetterCreateFrame.

I have to redraw with every key stroke so that the text gets updated, this means calling CTFramesetterCreateWithAttributedString and CTFramesetterCreateFrame.

Has anyone else come upon this problem, and if so, how did they get around it?

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EDIT:

Did some further investigating and turns out that if the attributed string has no attributes then everything draws so much faster and without any lag. Changing the font, color or paragraphs style all slow it down. Any idea if this could have something to do with it?

Answer 1

You probably should not be using CTFramesetter to create something like UITextView. Instead, you should likely keep an array of CTLine references. If you need help with word breaking, then you can use a CTTypeSetter, but you only need to hand it lines at the current caret and below (you'll still be creating and destroying typesetters a bit, so watch how much you ask of them).

One nice thing about keeping an array of CTLines is that you can throw away the ones you don't need if you're low on memory and reconstruct them later. Just keep track of the character range for each line.