iOS 11 touch cancelled - ios

Question

I have a custom drawing view in iOS. It's in Xamarin, but I do not think that is relevant.
I get a touch begin event, a couple of move events, then the touch is cancelled. Specifically if I move my finger a bit away from the original touch point. If I stay within a couple of mm from the original touch point, it is not cancelled.
The code worked in iOS 10, but now it has stopped working. I suspect this is due to some new feature in iOS 11, but I can't figure it out.
The view is not within a ScrollView of any kind, just a plain UIViewController.
Does anyone know of any SDK changes in iOS 11 doing this to my draw view?
[Register("SignatureDrawView")]
public class SignatureDrawView : UIView
{
private UIImageView drawImage;
private List<CGPoint> currentLine;
public SignatureDrawView()
{
InitializeDrawImage();
}
public SignatureDrawView(NSCoder coder) : base(coder)
{
InitializeDrawImage();
}
public SignatureDrawView(NSObjectFlag t) : base(t)
{
InitializeDrawImage();
}
public SignatureDrawView(IntPtr handle) : base(handle)
{
InitializeDrawImage();
}
public SignatureDrawView(CGRect frame) : base(frame)
{
InitializeDrawImage();
}
private void InitializeDrawImage()
{
Layer.BorderColor = UIColor.Black.CGColor;
Layer.BorderWidth = 0.5f;
drawImage = new UIImageView
{
BackgroundColor = UIColor.Red,
Image = new UIImage()
};
AddSubview(drawImage);
}
public override void LayoutSubviews()
{
base.LayoutSubviews();
drawImage.Frame = new CGRect(0, 0, Frame.Size.Width, Frame.Size.Height);
}
public override void TouchesBegan(NSSet touches, UIEvent evt)
{
UITouch touch = (UITouch)touches.AnyObject;
CGPoint point = touch.LocationInView(this);
currentLine = new List<CGPoint>();
currentLine.Add(point);
SetNeedsDisplay();
}
public override void TouchesMoved(NSSet touches, UIEvent evt)
{
UITouch touch = (UITouch)touches.AnyObject;
CGPoint point = touch.LocationInView(this);
currentLine.Add(point);
SetNeedsDisplay();
}
public override void TouchesCancelled(NSSet touches, UIEvent evt)
{
SetNeedsDisplay();
}
public override void Draw(CGRect rect)
{
UIGraphics.BeginImageContext(drawImage.Frame.Size);
drawImage.Image.DrawAsPatternInRect(new CGRect(0, 0, drawImage.Frame.Size.Width, drawImage.Frame.Size.Height));
UIColor.Black.SetColor();
if (currentLine != null && currentLine.Count > 3)
{
UIBezierPath path = new UIBezierPath();
path.LineWidth = 1f;
for (int i = 3; i < currentLine.Count; i++)
{
CGPoint p0 = currentLine[i - 3];
CGPoint p1 = currentLine[i - 2];
CGPoint p2 = currentLine[i - 1];
CGPoint p3 = currentLine[i];
path.MoveTo(p0);
path.AddCurveToPoint(p3, p1, p2);
}
currentLine.RemoveRange(0, 3);
path.Stroke();
}
drawImage.Image = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();
}
}

Answer 1

I found the answer. Throughout my app I use a side drawer, something like this: https://github.com/jdehlin/Xamarin-Sidebar.
The sidebar lib sets up a pan gesture for the drawer, and thet gesture recognizes probably cancelled my touch event. After disabling the drawer in that specific view, everything works as it shoud. I guess this is valid for normal iOS as well, not just Xamarin.