动态tableViewCell中imageView的宽高比

Question

I've got a tableView with 4 dynamic prototype cells: three of them for different kind of labels and one for an imageView.

In viewDidLoad() I use this code to determine the height of each cell based on their content:

tableView.estimatedRowHeight = 100
tableView.rowHeight = UITableViewAutomaticDimension

The problem is for the cell with the imageView. The picture to be displayed occupies almost all the cell and it needs to be shown in landscape keeping it's aspect ratio. I was able to do it, setting top, bottom, trailing, leading and height constraints: in this way the tableView could calculate the appropriate row.height.

Switching from iPhone 6 to 4, the image width is reduced but the height remains the same resulting in strange ratios.

I need to calculate the eight of the view based on the width of the moment and I tried it in two ways:

creating an NSLayoutConstraint outlet for the height. If I assign it a static value it works but when I try to calculate like:

constraintOutletForTheHeight.constant = CGFloat(myImageView.frame.size.width / 2)

it starts showing the first cells with the old value and the others appear with the computed height value.

I also attempted setting the aspectRatio constraint from Storyboard but in both cases Xcode tells me that it can't simultaneously satisfy constraints.

Thank you for your interest

Answer 1

After a lot of println() I found where I was wrong and a solution for that (not the most elegant but at least it works).

I discovered that the starting width of the imageView is the one assigned via storyboard (even after I set the imageView.image property) and after a bit of scrolling, it switches to presumed value: this is why I got constraint errors. As a solution in tableView:cellForRowAtIndexPath:, I used the tableView width property like this:

cell.<image_view_height_contraint>.constant = CGFloat(tableView.frame.size.width / 2)

If you know a better solution you're welcome otherwise I hope it could help someone else.