Retina display and [UIImage initWithData]

Question

I need to initialise images from raw data downloaded from a server which delivers the correct size of image based on the type of iPhone client.

I know that I should be setting the scale value to be 2.0 on the 640x960 display, however this is a readonly property and cannot be set during the init when using initWithData.

Any ideas?

Answer 1

I'm not aware of anything you can embed in the image data itself to tell the phone that it's a @2x image, but something like this should work:

UIImage * img = ...;
img = [UIImage imageWithCGImage:img.CGImage scale:2 orientation:img.imageOrientation];

Answer 2

由于iOS 6.0 UIImage有方法+ imageWithData:scale:你可以传递2.0作为视网膜的比例。

Answer 3

您可以将[[UIScreen mainScreen] scale]作为scale参数而不是2.0f 。

Answer 4

Swift3,4版本

let image = UIImage(data: imageData, scale: UIScreen.main.scale)

Answer 5

put this in your .m if you want or on an imported class (the syntax of c is nicer when calling the function IMAO)

BOOL isRetina(){
    if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
        return [[UIScreen mainScreen] scale] == 2.0;
    }
    return NO;
}

Then when creating the image with the server data:

[UIImage imageWithData:dataFromServer scale:isRetina()?2:1];

Answer 6

AFAIK you don't need to set the scale value yourself. The OS will handle the points to pixel translation for you.