iPhone: How to extend a repeatable UIImage?

Question

I have an image which I use to frame a tweet. It consists of two rounded rects, with a twitter icon a the top left. The important part is that it is repeatable, as you could copy any part of the middle section vertically, and it would be the same, just longer. Here is the image I created:

My question is how, in code, do I extend (or shrink) that dependent on how many lines are in my UITextView? Something like this to get the size:

float requiredHeight = lines * 14;

I know this is possible, because apple do it with their SMS app :)

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UPDATE: Here is the complete code for doing this:

UIImage *loadImage = [UIImage imageNamed:@"TwitPost.png"];
float w2 = loadImage.size.width/2;
float h2 = loadImage.size.height/2;
// I have now reduced the image size so the height must be offset a little (otherwise it stretches the bird!):
loadImage = [loadImage stretchableImageWithLeftCapWidth:w2 topCapHeight:h2+15];
imageView.image = loadImage;

Thanks for both answers.

Answer 1

By using

- (UIImage *)stretchableImageWithLeftCapWidth:(NSInteger)leftCapWidth topCapHeight:(NSInteger)topCapHeight

Where you set leftCapWidth and topCapHeight as half the width and height of your image. This image you can stretch in a UIImageView by changing its bounds/frame.

Answer 2

Look at the documentation for UIImage. Specifically:

- (UIImage *)stretchableImageWithLeftCapWidth:(NSInteger)leftCapWidth topCapHeight:(NSInteger)topCapHeight

This allows you to use an image which repeats the portion at the leftCapWidth or topCapHeight to stretch it horizontally or vertically.