what is the difference between UIImageView and drawInRect?

Question

Hi, I want to display so many images in table cells. I knew two methods to show an image.

One is creating an instance to UIImageView and show it

CGRect rect=CGRectMake(x,y,width,height);
UIImageView *image=[[UIImageView alloc]initWithFrame:rect];
[image setImage:[UIImage imageNamed:@"sample.jpg"]];

Another method is,

CGRect rect=CGRectMake(x,y,width,height);
[[UIImage imageNamed:@"sample.jpg"] drawInRect:rect];

Now, my question is, what is the difference between these two? Which one is efficient? Or someother function is available better than this?

Thanks in advance....

Answer 1

UIImageView is a UIView subclass. By adding it to the view hierarchy you get all the free benefits: animations, size properties, affine transoforms, etc. Plus, you are able to change the underlying UIImage any time you want.

On the other hand, calling drawInRect: will just draw the image where you tell it to, but not interact with the UIView hierarchy, so you don't gain any of the benefits from having it on the view hierarchy.

I would think (have not tried it), that drawing the image directly is faster, but I would think in most of the cases having a UIImageView is a better idea.

Answer 2

Using the drawInRect: method has CoreGraphics draw the image into the active CGContext using the CPU. Assuming you're in a UIView's drawRect: method, this will paint the image into the view's buffer.

UIImageView uses whichever image is assigned to it as it's backing buffer instead of using the slower drawRect:. The GPU then references this buffer directly when the screen is composited via QuartzCore.