How to get image without resizing? - ios

Question

first of all i need to describe what i gonna to do:
i need to display a header image with full screen width for all devices.
there for i should provide multiple pictures with different sizes, and not just 2x and 3x.
so i would have these images:
header_width_1242.png for iphone 6 plus.
header_width_1125.png for iphone 6 plus display zoom
header_width_640.png for iphone 5,6
...
so i shouldn't choose image according to the scale, rather i should choose image according to the width:
let image_name = "header_width_" + String(UIScreen.mainScreen().scale * UIScreen.mainScreen().bounds.width)
let image = UIImage(named:image_name)
the problem, that ios scale the image automatically again. so if the device with scale 2x. then it return the image * 2 size.
e.g : for iphone 5 which has width 320 and scale 2, i need the header_width_640.png , but it seems that the system scale the image to 1280 (640 * 2).
How could i tell the system, to return image UIImage(named:image_name) without scaling ?thanks

Answer 1

You could declare a screenSize property on your viewController.
// Determine screen size
let screenSize: CGRect = UIScreen.mainScreen().bounds
Then, when you need to set an image, you could do the following:
if screenSize.width < 641 {
// set your imageView to the image for 640 screen width
} else if screenSize.width < 1126 {
// set your imageView to the image for 1125 screen width
} else if screenSize.width < 1243 {
// set your imageView to the image for 1242 screen width
}

Answer 2

You should not constraint assets by screen size, is better if you do by using size classes if available. Image assets directory make this possible in the inspector panel, by choosing the size classes for each image.
I do understand that sometimes is a need, but try to think in a relative perspective. If the image is something like a logo aligned by left or right you can use slicing to create stretchable end/beginning on the image.
If the image is center with a solid color or something drawable by code you can draw it at run time.
Here is a snippet in ObjC that use in an app of mine you can easily convert in SWIFT:
-(UIImage*) createNavBarBackgroundWithImage:(UIImage*) image {
CGSize screenSize = ((CGRect)[[UIScreen mainScreen] bounds]).size;
CGFloat width = screenSize.width;
CGFloat height = 64.0;
UIGraphicsBeginImageContextWithOptions(CGSizeMake(width, height), NO, 0.0);
//Draw background
UIColor * backGroundColor = [UIColor colorWithRed:27.f/255.f green:142.f/255.f blue:138.f/255.f alpha:1.0];
[backGroundColor setFill];
UIRectFill(CGRectMake(0, 0, width, height));
//Draw the image at the center
CGPoint point = CGPointMake(width/2 - image.size.width/2, 0);
[image drawAtPoint:point];;
UIImage *newBGImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newBGImage;
}

Answer 3

Use Image Asset
https://developer.apple.com/library/ios/recipes/xcode_help-image_catalog-1.0/chapters/AddingImageSets.html
header_width_1242.png for iphone 6 plus. Name it header_width_414.png drag to 3x
header_width_1125.png name it header_width_375.png drag to 3x
header_width_640.png name it header_width_320.png drag to 2x
let image_name = "header_width_" + UIScreen.mainScreen().bounds.width)
let image = UIImage(named:image_name)