iOS 11 getting visibleHeight and contentInset from a UITableView or UIScrollView

Question

Pre iOS 10

if I wanted to get the visible height of a table or scroll view, I had to subtract the top and bottom inset from the height of the tableview

let tableView = ....
let height = tableView.frame.size.height - tableView.contentInset.top - tableView.contentInset.bottom

iOS 11

Unfortunately on iOS 11 suing the above method, I was am not getting the correct value.

After some debugging I realised that the top inset was 0.0, instead of the height of my navigation bar.

Answer 1

iOS 11 and UIScrollViewContentInsetAdjustmentBehavior

I am not getting the correct contentInset, as iOS 11 introduced UIScrollViewContentInsetAdjustmentBehavior. More information can be found on the following link:

https://developer.apple.com/documentation/uikit/uiscrollview/2902261-contentinsetadjustmentbehavior

Since UIScrollViewContentInsetAdjustmentBehavior was introduced, we have to take into account the adjustedContentInset property and add it to the contentInset.

The above code has to be updated to the following:

let visibleHeigh: CGFloat
if #available(iOS 11, *) {
  visibleHeight = tableView.frame.size.height - (tableView.contentInset.top + tableView.adjustedContentInset.top) - (tableView.contentInset.bottom + tableView.adjustedContentInset.bottom)
} else {
  visibleHeight = tableView.frame.size.height - tableView.contentInset.top - tableView.contentInset.bottom
}

Answer 2

if you want the content inset of the scroll view to be unaffected by the "adjustedContentInset", you can disable this unpredictable behavior with the following code:

// obj-c
if (@available(iOS 11.0, *)) {
  [tableView setContentInsetAdjustmentBehavior:UIScrollViewContentInsetAdjustmentNever];
}

// swift
if #available(iOS 11.0, *) {
  tableView.contentInsetAdjustmentBehavior = .never
}