Question

I have two UIScrollView instances and I want to draw a vertical line between them (not 100% height, more like 80%). How can I achieve this?

Answer 1

Use Core Graphics. Nest the two UIScrollViews inside another view and override the drawRect method on the parent. See Apple’s UIView documentation for drawRect for more detail and the Core Graphics Context Reference for more information about drawing.

- (void) drawRect: (CGRect) rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();

    // Draw divider
    UIGraphicsPushContext(context);
        // Fill the background, this must happen if the view is not opaque.
            if (self.opaque)
            {
            [[UIColor whiteColor ] set];
            CGContextFillRect(context, rect);
            }

        [[UIColor grayColor] set];

        CGContextSetLineWidth(context, 1);

        CGContextBeginPath(context);
        CGContextMoveToPoint(context, rect.size.width * 0.5, 0.1 * rect.size.height);
        CGContextAddLineToPoint(context, rect.size.width * 0.5, 0.9 * rect.size.height);
        CGContextStrokePath(context);
    UIGraphicsPopContext(); 
}

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edit

To address my oversight, there is no simple way that I know of to draw on top of subviews.

This behavior can be simulated using the same basic view hierarchy as above. Subclass UIView to create a completely transparent view that does not accept any touch events. Place the drawing code (I added a conditional for opacity in the code above) in the custom view and then insert an instance of the custom view at the front of the view hierarchy.