difference between UIImageView.image = ... and UIimageView.layer.content = - ios

Question

Two ways of set UIImage to A UIImageView:
First:
self.imageview.image = [UIImage imageNamed:#"clothing.png"];
Second:
self.imageview.layer.contents = (__bridge id _Nullable)([[UIImage imageNamed:#"clothing.png"] CGImage]);
what is the difference between the two ways?
which one is better?
In fact.What I want to do is displaying part of one PNG in UIImageView.
There are two ways:
First:
UIImage *image = [UIImage imageNamed:#"clothing.png"];
CGImageRef imageRef = CGImageCreateWithImageInRect(image, rect);
self.imageview.image = [UIImage imageWithCGImage:imageRef];
Second:
self.imageview2.layer.contents = (__bridge id _Nullable)([[UIImage imageNamed:#"clothing.png"] CGImage]);//way2
self.imageview2.layer.contentsRect = rect;
Which one is better? Why? Thanks!

Answer 1

First:
self.imageview.image = [UIImage imageNamed:#"clothing.png"];
By using this you can directly assign your image to any UIImageView While in
Second:
self.imageview.layer.contents = (__bridge id _Nullable)([[UIImage imageNamed:#"clothing.png"] CGImage]);
You can not assign image directly to layer. so you need to put a CGImage into a layer.
So First is best forever. Thank you.

Answer 2

First option is better, Bridge concept is used before introduction of ARC

Answer 3

Of course the better way is the first one :
self.imageview.image = [UIImage imageNamed:#"clothing.png"];
Indeed, this is the way an UIImageView is built for.
For clarification, every view (UIView, UIImageView, etc) has a .layer property to add visual content on it. Here you're adding an image in it. You could have achieved the same result with a single UIView. But, in performances terms and clarity, you should (have to) use .image property.
Edit :
Even with your new edit, first option is still the better one.

Answer 4

You can do that but it's your responsibility to modify the image to make the image.CGImage draw correctly respect to imageOrientation, contentMode and so on. If you set the image with imageView.image = image;, it's apple's responsibility to do that.
I give you an example that causes the problem:
as image.CGImage doesn't contain image orientation, so if you set it directly and if the source image is not UIImageOrientationUp, the image will be rotated, unless you "fix the orientation" of the source image like this. (You can get a image that is not UIImageOrientationUp, just take a photo with your iPhone)
- (UIImage *)fixOrientation {
if (self.imageOrientation == UIImageOrientationUp) return self;
UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
[self drawInRect:(CGRect){0, 0, self.size}];
UIImage *normalizedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return normalizedImage;
}
Here are two screen shot, the first is set image.CGImage directly to layer.contents, the second is set image to imageView.image.
So always use imageView.image unless you know what you're doing.