I\'ve been trying to make this work for days now, with no luck, so I thought I\'d share info and maybe someone comes up with a solution.
I want to get the exact viewport
In the view I wanted to take the height of the remaining screen after the virtual keyboard was on, I was using an absolutely overflown element that covered the whole screen using screen height and the content of the whole page was inside of it. As a result, the virtual keyboard was opening on TOP of the overflown element, without changing its dimensions.
To fix the specific problem, all I had was change the position of this element to static and remove the overflow when the virtual keyboard was opened - actually ios changes to THIS behaviour by default when issuing he virtual keyboard (changes elements to static position) and this is why the fixed elements become static.
I hope this helps.