Xcode 6 UIImageView无法正确缩放

Question

Please see screen shot of flower setup below. The flower image has been correctly loaded from an asset catalog and when the app is run on various simulators the correct pixel resolution is assigned to each device. My problem is how to get the flower image to be scaled (equally sized to fit) the same on each device ?? I have learnt how to position the image to different positions using constraints and frames but the image never scales correctly - please see first pic

The following image is a mock up of what I want to be able to do (flower image scaled correctly on each device)

Answer 1

Judging by your mockups, it looks like you want the image to fill half the width, and keep its square aspect ratio to determine its height. One way to approach this would be to use AutoLayout to make a left UIImageView and a right placeholder (blank) view. Pin the left view to the left edge of the parent, the right view to the right edge, and then set them to be 0 pixels from each other. Then set an equal widths constraint on them. Finally, control drag the image view to itself and you can select aspect ratio -- and assuming that in IB, the width and height is the same, it will keep it square. Adding an equal heights constraint will give the other view the height it needs to be equal in case you need that.

This gives you a left image view that is 50% and with your mode set to Aspect Fit or Aspect Fill, it should give you the results in your mockups. In case you have an image that isn't square, make sure to check Clip Subviews for your UIImageView to prevent showing the overflow.

Answer 2

The real problem is that your goals are not well defined. Scaled with respect to what ? The screen has a height and a width. You can't scale with respect to both, because that would distort the image (because different devices have different overall aspect ratios). Thus you have to pick one dimension that you will scale to.

Judging from your mockup, I'm going to guess that what you want is to scale with respect to height . If so, then give the image view a height constraint that is a fixed fraction of its superview's height. It looks to be about 0.25 in your mockups but you will have to eyeball what you think is a good fraction.

Now, if the content mode of the image view is Aspect Fit (or Aspect Fill), the image will change its height along with the image view without distorting the aspect ratio.

However, it would be best if you would make the other dimension (here, the width) of the image view a fixed fraction of the height, such as to make the aspect ratio of the image view the same as the aspect ratio of the image. The reason is that otherwise the image might end up centered in the image view in such a way that it doesn't touch the top or left any more, even though the image view itself does.

Answer 3

CGFloat screen_width = [[UIScreen mainScreen] bounds].size.width;
your_imageview.frame = CGRectMake(0, 0, screen_width/2, screen_width/2);