Overridden Draw method of ViewRenderer blocks UI - ios

Question

I implement a Xamarin.Forms control. The problem I'm currently experiancing is that an overridden Draw() method of a custom renderer blocks UI (at least for iOS platform). I've googled but with no success. Is is possible to perform the drawing in a background without blocking the UI?
Here is the code of a simple renderer for iOS platform that that demonstrates the issue.
public class MyCustomRenderer : ViewRenderer
{
protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
{
base.OnElementPropertyChanged(sender, e);
SetNeedsDisplay();
}
public override void Draw(CoreGraphics.CGRect rect)
{
var myControl = (MyControl)this.Element;
if (!myControl.IsRendered)
{
using (var context = UIGraphics.GetCurrentContext())
{
var token = CancellationToken.None;
var task = Task.Factory.StartNew(() => TimeConsumingRendering(context, token), token);
// task.Wait() blocks the UI but draws the desired graphics.
// When task.Wait() is commented out = the desired graphics doesn't get drawn and it doesn't block the UI
task.Wait();
}
}
}
private void TimeConsumingRendering(CGContext context, CancellationToken token)
{
try
{
for (int i = 0; i <= 100; i++)
{
token.ThrowIfCancellationRequested();
var delay = Task.Delay(50);
delay.Wait();
}
context.ScaleCTM(1f, -1f);
context.TranslateCTM(0, -Bounds.Height);
context.SetTextDrawingMode(CGTextDrawingMode.FillStroke);
context.SelectFont("Helvetica-Bold", 16f, CGTextEncoding.MacRoman);
context.SetFillColor(new CoreGraphics.CGColor(1f, 0f, 0f));
context.ShowTextAtPoint(0, 0, "Finished");
}
catch
{ }
}
}

Answer 1

Looks like that the only solution for that is to separate the time consuming drawing and drawing on the actual control.
The solution is
to generate an image in a background(triggered by an event). and only than use it within the Draw method.
to use the generated image within the overridden Draw method.
At least it works for me.