Efficiently draw line numbers + cursor with UITextView - ios

Question

I'm trying to implement something like code-editor. I base my work on CYRTextVIew. Everything works fine except for line numbers and cursor drawing.
First of all it has a bug, which doesn't erase previous cursor position, which results in drawing multiple ones, looks like so:
Here is the code related to that:
- (void)drawRect:(CGRect)rect
{
// Drag the line number gutter background. The line numbers them selves are drawn by LineNumberLayoutManager.
CGContextRef context = UIGraphicsGetCurrentContext();
CGRect bounds = self.bounds;
CGFloat height = MAX(CGRectGetHeight(bounds), self.contentSize.height) + 200;
// Set the regular fill
CGContextSetFillColorWithColor(context, self.gutterBackgroundColor.CGColor);
CGContextFillRect(context, CGRectMake(bounds.origin.x, bounds.origin.y, self.lineNumberLayoutManager.gutterWidth, height));
// Draw line
CGContextSetFillColorWithColor(context, self.gutterLineColor.CGColor);
CGContextFillRect(context, CGRectMake(self.lineNumberLayoutManager.gutterWidth, bounds.origin.y, 0.5, height));
if (_lineCursorEnabled)
{
self.lineNumberLayoutManager.selectedRange = self.selectedRange;
NSRange glyphRange = [self.lineNumberLayoutManager.textStorage.string paragraphRangeForRange:self.selectedRange];
glyphRange = [self.lineNumberLayoutManager glyphRangeForCharacterRange:glyphRange actualCharacterRange:NULL];
self.lineNumberLayoutManager.selectedRange = glyphRange;
[self.lineNumberLayoutManager invalidateDisplayForGlyphRange:glyphRange];
}
[super drawRect:rect];
}
I changed one line to this:
[self.lineNumberLayoutManager invalidateDisplayForGlyphRange:NSMakeRange(0, self.text.length)];
And it fixed that. But never mind: both approaches are painfully slow when it comes to UITextView scrolling. It is completely not suitable for production, since working with UITextView is uncomfortable. I also would love to add "error" functionality later, so I could draw red cursor in the places where error occurs.
So the question is, what is the best and the most efficient way to achieve that type of functionality?
Why I told about the bug? I told this to underline that my requirement is to have dynamically positioned cursor, which points only to current line, and you also should note that cursor rect may be much longer that regular line width if line doesnt fit into TextView's frame's width (i.e. line 8 and 9).