Draw method doesn't get called from the custom UIView - ios

Question

I'm creating a custom map pin (annotation) for iOS, draw its path and then convert the UIView to an image, using this method:
public static UIImage AsImage(this UIView view)
{
try
{
UIGraphics.BeginImageContextWithOptions(view.Bounds.Size, true, 0);
var ctx = UIGraphics.GetCurrentContext();
view.Layer.RenderInContext(ctx);
var img = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();
return img;
}
catch (Exception)
{
return null;
}
}
and this is the UIView-derived class, where I draw the annotation path:
public class PinView : UIView
{
public PinView()
{
ContentMode = UIViewContentMode.Redraw;
SetNeedsDisplay();
}
private readonly CGPoint[] markerPathPoints = new[]
{
new CGPoint(25f, 5f),
new CGPoint(125f, 5f),
//other points };
public override void Draw(CGRect rect)
{
base.Draw(rect);
//get graphics context
CGContext context = UIGraphics.GetCurrentContext();
//set up drawing attributes
context.SetLineWidth(10);
UIColor.White.SetFill();
UIColor.Black.SetStroke();
//create geometry
var path = new CGPath();
path.MoveToPoint(markerPathPoints[0].X, markerPathPoints[0].Y);
for (var i = 1; i < markerPathPoints.Length; i++)
{
path.AddLineToPoint(markerPathPoints[i].X, markerPathPoints[i].Y);
}
path.CloseSubpath();
//add geometry to graphics context and draw it
context.AddPath(path);
context.DrawPath(CGPathDrawingMode.FillStroke);
}
I'm modifying the Xamarin.Forms sample of the MapCustomRenderer, instead of loading the annotation from a file, I'm loading it from the view:
annotationView.Image = new PinView().AsImage();
but the PinView.Draw() never get called!

Answer 1

The method Draw will been invoked after the method ViewDidLoadwhen the control first been loaded , which is called automatically by the system .
In your case , you didn't set the Rect(Frame) of the PinView . So the method Draw will never been called because the Rect is zero in default .
So you could set a default frame in the constructor
public PinView()
{
Frame = new CGRect (0,0,xx,xxx);
ContentMode = UIViewContentMode.Redraw;
SetNeedsDisplay();
}

Answer 2

The view needs to be added to the views hierarchy, in my case, to the MKAnnotationView,
so in the CustomMKAnnotationView constructor:
public CustomMKAnnotationView(IMKAnnotation annotation, string id)
: base(annotation, id)
{
var pin = new PinView(new CGRect(0, 0, 110, 110));
pin.BackgroundColor = UIColor.White.ColorWithAlpha(0);
Add(pin);
}
and in the UIView's constructor, the Frame should be initialized as Lucas Zhang stated:
public PinView(CGRect rectangle)
{
Frame = rectangle;
ContentMode = UIViewContentMode.Redraw;
SetNeedsDisplay();
}
With these changes the Draw method is called.