问题
If I want to set a button's background image in iOS in an app that uses autolayout, what size should the .png image be? Since the height, and width of the button will always vary, in addition to accommodating for retina/nonretina displays (@2x?).
回答1:
You can add multiple images with providing proper naming conventions normal, @2x, @3x, ~iPad etc.
For that go through Apple documentations.
For example, your image name is myBackground.png then
[UIImage imageForDeviceWithName:@"myBackground"];
Then here is the list of files and resolutions for "myBackground"
myBackground@2x.png == 960 × 640
myBackground-568h@2x.png == 1136 × 640
myBackground-667h@2x.png == 1334 × 750
myBackground@3x.png == 2208 × 1242
myBackground~ipad.png == 1024 × 768
myBackground@2x~ipad.png == 2048 × 1536
Same way you require to add images for landscape with suffix added like: ~Landscape
回答2:
When You are using Image for particular Button then you should note down the following point
- When your Button is size of 50x100 then the Image should be with size 50x100 for non-ratina. and Button is size of 50x100 then the Image should be with size 100x200 for Ratina.
In short doesn't matter with your Button size. when you are using any Image with X size for Non Ratina then for Ratina display required same Image with 2X (double size) image.
X size for Non Ratina
2*x size for Ratina
because it will work every device but your Button Image will not seen properly.
来源：https://stackoverflow.com/questions/27741808/size-of-images-for-ui-for-different-screen-sizes