[iOS Accessibility] Bugfix: VoiceOver always seeing fields for all entry types

[eliykat]

Objective

Bugfix for #1197:

No matter what type of entry you're creating or viewing, VoiceOver is seeing the text fields for every other type of entry (IE, if creating a secure note you see text fields for username, password, credit card number and so on)

The cause of the bug was that VoiceOver (the iOS screenreader) reads invisible elements (i.e. those with IsVisible="False"). However, IsVisible is the primary means for showing/hiding relevant/irrelevant fields and controls.

Code Changes

Whether an element is “visible” to VoiceOver is determined by a separate property, AutomationProperties.IsInAccessibleTree. However, unlike IsVisible, this does not affect child items, so it cannot effectively be applied to a parent StackLayout to hide its children from VoiceOver.

I have therefore generally taken the following approach:

• Where IsVisible is set on an individual element, set IsInAccessibleTree on that element with the same value.
• Where IsVisible is set on a layout element, add IsInAccessibleTree to each child with the same value as the parent.
• However, I didn't do this for the main controls for each item type, because of the large number of elements. Instead, they are added/removed from the element tree as required using code behind.

Issues

The Add URI button is still being picked up by VoiceOver on the AddEdit page, even when it's invisible and IsInAccessibleTree is set to False. I figure I'd looked at this long enough, maybe someone else can spot what's going on.

Other than that, I have tested this on my iPhone 6 and it all works as expected.

[cscharf]

Perhaps a custom render, or renderers would be appropriate or if there is another Xamarin.Forms extension that can be hooked into for this in a more generic way to handle screen reader updates across the board, especially for container/layout visibility changes.
@mportune-bw , any thoughts/ideas on this one?

[eliykat]

After some investigation, I think this could be done much cleaner with a custom renderer to set the native iOS property accessibilityElementsHidden on StackLayout and Grid elements. This property appears to remove an element's children from the accessibility tree, but is not set by the Xamarin.Forms default renderer.

However, in the course of testing a solution to this, I upgraded the Xamarin.Forms package from 4.5.0.725 to 5.0.0.1874 (latest release), and this seems to have fixed the bug entirely.

To make sure, I cloned a fresh copy of the mobile repo, fetched nuget packages, upgraded Xamarin.Forms, and with no other changes the bug disappeared on my iPhone 6 (iOS 12.5).

Can someone else verify this - perhaps on a newer model iPhone?

@cscharf

[mpbw2]

Bumps to Forms require a fair amount of regression testing before we can ship. I'm using 5.x in a work branch and it touches a lot coming from 4.5.x. If also fixes this bug entirely we should probably hold off on this PR.

[cscharf]

Bumps to Forms require a fair amount of regression testing before we can ship. I'm using 5.x in a work branch and it touches a lot coming from 4.5.x. If also fixes this bug entirely we should probably hold off on this PR.

Agreed... @eliykat , let's hold off on this one since it appears the update Matt is already working on will resolve this issue. Good find on that!

[eliykat]

Closing this, as the changes in this PR are unlikely to be relevant once the Xamarin Forms upgrade is complete.