How to draw a rectangle in xamarin.mac

Question

I'm trying to draw a rectangle in the xamarin.mac framework. It seems like this can be accomplished with the CoreGrpahics namespace but I'm not sure how it hooks up with xamarin. For example

        NSColor.Black.Set();
        NSBezierPath.StrokeLine(new CGPoint(-10.0f, 0.0f), new CGPoint(10.0f, 0.0f));

Does not make anything appear on the screen, when i believe it should make a single line appear. This seems trivial in the other Xamarin. frameworks as there are built in functions available, but the xamarin.mac documentation is very sparse.

Answer 1

Welcome! Glad to see more Xamarin.Mac users.

@SushiHangover hinted at it but you need to be in a valid draw context. Pardon if I'm over-explaining, but custom drawing like you're discussing is often done in a NSView, typically by overriding a view's DrawRect(CGRect dirtyRect) method. That method is inherently called by AppKit within the proper graphics context. So your code would work fine if called within that method of a view. Keep in mind that those drawing methods are called very often and must be efficient.

If you were to use a CGPath instead of a NSBezierPath, you need to add that path to the context by calling NSGraphicsContext.CurrentContext.CGContext.addPath(path) .

I've made a little Xamarin workbook titled "MacOS Custom Drawing" for ya here that shows both ways: https://github.com/NickSpag/Workbooks . I'd also recommend Workbooks for drawing practice and testing, as they make it very easy to continually and quickly reload your code.

Answer 2

this code from the Xamarin docs draws a triangle, but should give you the basic idea. The CoreGraphics API should be the same for iOS and Mac, so an example for one should easily translate to the other

//get graphics context
using (CGContext g = UIGraphics.GetCurrentContext ()) {

    //set up drawing attributes
    g.SetLineWidth (10);
    UIColor.Blue.SetFill ();
    UIColor.Red.SetStroke ();

    //create geometry
    var path = new CGPath ();

    path.AddLines (new CGPoint[]{
    new CGPoint (100, 200),
    new CGPoint (160, 100), 
    new CGPoint (220, 200)});

    path.CloseSubpath ();

    //add geometry to graphics context and draw it
    g.AddPath (path);       
    g.DrawPath (CGPathDrawingMode.FillStroke);
}