Why doesn't CoreGraphics FillPath fill the specified path - core-graphics

Question

I've got some Xamarin.iOS CoreGraphics code that draws red triangles at the ends of several white lines of various angles.
I want have the red triangles filled in instead of being rendered as outlines but when I use the graphic context command FillPath() instead of StrokePath() the red triangles don't appear.
Here's the DrawArrowHead code (called by the line drawing code after each individual line is drawn).
private void DrawArrowHead(PointF[] line, int size)
{
// Create the arrowhead and the lines from individual arrowhead points
PointF[] arrowhead = new PointF[] {
new PointF(0.0f - size, 0.0f),
new PointF(0.0f, 0.0f - size),
new PointF(0.0f + size, 0.0f)
};
PointF[] line1 = new PointF[] {new PointF(arrowhead[0].X, arrowhead[0].Y), new PointF(arrowhead[1].X, arrowhead[1].Y)};
PointF[] line2 = new PointF[] {new PointF(arrowhead[1].X, arrowhead[1].Y), new PointF(arrowhead[2].X, arrowhead[2].Y)};
PointF[] line3 = new PointF[] {new PointF(arrowhead[2].X, arrowhead[2].Y), new PointF(arrowhead[0].X, arrowhead[0].Y)};
// Begin drawing the arrowhead
gctx.SaveState();
UIColor.Red.SetStroke();
gctx.SetFillColor(UIColor.Red.CGColor);
gctx.BeginPath();
double angleInRadians = Math.Atan2 (line[0].Y - line[1].Y, line[0].X -line[1].X);
gctx.TranslateCTM(line[1].X, line[1].Y);
gctx.RotateCTM((float)(angleInRadians - Math.PI / 2));
path.AddLines(line1);
path.AddLines(line2);
path.AddLines(line3);
path.CloseSubpath();
gctx.AddPath(path);
gctx.StrokePath();
gctx.RestoreState();
}
When I replace gctx.StrokePath() with gctx.FillPath() I get the white lines but no arrowheads.
When I replace gctx.StrokePath() with gctx.DrawPath(CGPathDrawingMode.FillStroke) I get the red triangles but they're not filled in.
I'm sure it's something simple that I'm missing. Thanks in advance.
Update - 03.22.13
Turns out #poupou's answer was correct but, compounded by some of my other coding "misinterpretations," didn't solve my problem right away. However, since it pointed me in the right direction towards a solution I'm accepting his answer.
I first learned how to use CoreGraphics via Mike Bluestein's excellent Drawing with CoreGraphics in MonoTouch post. However, a little knowledge is a dangerous thing and when I began applying these concepts to my own work, I inadvertently mixed graphics context and path methods when I shouldn't have.
After a lot of googling, reading, and reviewing other peoples CoreGraphics source code (props to Nina Vyedin and Bryan Costanich of Xamarin for their Drawing sample), I came up with a DrawArrowhead method that works.
private void DrawArrowHead(PointF[] line, int size)
{
gctx.SaveState();
UIColor.Red.SetStroke();
UIColor.Red.SetFill();
double angleInRadians = Math.Atan2 (line[0].Y - line[1].Y, line[0].X -line[1].X);
gctx.BeginPath();
gctx.TranslateCTM(line[1].X, line[1].Y);
gctx.RotateCTM((float)(angleInRadians - Math.PI / 2));
PointF[] arrowhead = new PointF[] {
new PointF (0.0f - arrowHeadSize, 0.0f),
new PointF (0.0f, 0.0f - arrowHeadSize),
new PointF (0.0f + arrowHeadSize, 0.0f)
};
gctx.MoveTo(arrowhead[0].X, arrowhead[0].Y);
gctx.AddLineToPoint(arrowhead[1].X, arrowhead[1].Y);
gctx.AddLineToPoint(arrowhead[2].X, arrowhead[2].Y);
gctx.ClosePath();
gctx.DrawPath(CGPathDrawingMode.FillStroke);
gctx.RestoreState();
}
Here's the final result.
Note: I had to move the DrawArrowHead code out of it's method and into my UIView's Draw method to avoid Invalid Context errors when drawing the second, third, fourth, and fifth line/arrowhead combinations (you can read about that type of error here).

Answer 1

Calling path.CloseSubpath(); on a CGPath is not identical to calling gctx.ClosePath(); on a CGContext (where the stroke/fill will be done). Did you try the later ?