How do I control the auto-scroll of an iOS Xamarin editor when the soft keyboard appears? - ios

Question

I'm encountering some bizarre behaviour in a Xamarin Forms iOS Editor.
I have needed the editor to expand horizontally with the width of the text, rather than wrapping.
To achive this, I placed the Editor inside a ScrollView:
<local:ScrollViewEx x:Name="svContent" HorizontalScrollBarVisibility="Default" Orientation="Both"
BackgroundColor="Transparent">
<local:EditorEx x:Name="edContent"
VerticalOptions="Fill" HorizontalOptions="Fill"
WrapLongLines="False"
BackgroundColor="Transparent" />
</local:ScrollViewEx>
In the editor renderer, everytime the text changes, I resize the editor's height and width by getting new dimensions from the following method:
Size GetSizeThatFits()
{
CGSize newSize = Control.SizeThatFits(new CGSize(nfloat.MaxValue, nfloat.MaxValue));
return new Size(newSize.Width, newSize.Height);
}
This all works fine.
But when the editor takes focus and the soft keyboard appears, the system will always horizontally scroll to the maximum x value of the line where the cursor sits. This can cause the cursor to be moved offscreen, and will obviously create confusion for users.
I have tried to control the scrolling by holding the x value in place and only allowing an autoscroll of Y as follows:
private void Editor_Focused(object sender, FocusEventArgs e)
{
double x = sv.ScrollX;
Device.BeginInvokeOnMainThread(() =>
{
sv.ScrollToAsync(x, sv.ScrollY, false);
});
}
This succeeds in holding my x value in place, but now Y for some reason is being automatically set to zero, ignoring the value of sv.ScrollY.
Any ideas?
UPDATE 01
I've just tested the app on an iPhone12 device and the problem is even worse.
With every keystroke the scroll will jump to a different part of the screen.
Is there anyway to completely decouple the keyboard and my Editor/ScrollView scrolling? It would be easier for me to write my scrolling behaviour completely by myself than to keep fighting with the built in behaviour which is not making sense.
UPDATE 02
I may be getting a little closer to my goal.
By subclassing my UITextView and enclosing UIScrollView and overriding their scroll related methods I've manage to kill off most of their unpredictable scroll behaviour:
public override void ScrollRectToVisible(CGRect rect, bool animated)
{
//do nothing
}
public override void SetContentOffset(CGPoint contentOffset, bool animated)
{
//do nothing
}
However some remains. The following scenario is causing problems:
TextChanged event
Reconstruct a UIStringAttributes based on new text, and assign it to Control.AttributedText (Scroll has stayed stable up to this point)
Control.TextStorage.BeginEditing();
Control.AttributedText = astr;
Control.TextStorage.EndEditing();
The next click on the editor to trigger cursor position / SelectionChange however causes an editor scroll setting ScrollY, and sometimes ScrollX to zero.
Why????
Step 3 is hard for me to manage because SelectionChange occurs with both a click on the editor and the entry of text. It also occurs before a TextChange so is hard to predict the cause of SelectionChange.
In addition, even if I bypass Step 2 and don't manually reset my AttributedText, the jump at Step 3 still occurs.
Any ideas?