如何加快对UITextView的更新？

Question

I have a calculator app with an “accounting tape” made of UITextView . Once there's around 50–100 lines on the tape, the text view gets quite slow to update – setting new contents (50–100 lines of text) easily takes 100 ms or more. The problem is that I can't move this delay to the background, since UIKit insists on being called on the main thread.

What can I do? About the only thing that comes to mind is rewriting the tape using a custom UIView subclass that would be better suited to the task, but I'm not very eager to do that as it's a lot of work and the UITextView works fine apart from this problem.

Answer 1

I'm very surprised that you're having a problem when only dealing with 50 lines, so I frankly wonder if there's something else going on here. I'd run the code through the "Time Profiler" in Instruments and confirm that the problem really is the updating of the UITextView and not something else. A little research here might be warranted before giving up on UITextView ,

But let's assume for a second that you decided that you need to start over (which I find unlikely) and not use UITextView . I might suggest leveraging existing control, eg a UITableView with no separator between cells or, if worst came to worst, a UIScrollView where each line on the tape is a UILabel and you do a UITableView -style dequeuing of labels that have scrolled off the screen. A bunch of options that are a little better than starting from scratch.

Answer 2

Assuming it's really the UITextView that is slow and not something else, I would suggest you alter the text of the textview to only that part, which is visible. All the text that has scrolled outside doesn't need to be kept in the textview. Of course you would have to implement your own scrolling then if you need that or use blank lines for the removed ones so the scrolling behavior keeps intact.