[FIXED] Creating a UIView subclass that uses a CAGradientLayer as its layer


I want to port this to C#.

I don’t know how I should convert this:

@property (nonatomic, strong, readonly) CAGradientLayer *layer;

The layer is the default layer for the UIView. Xamarin already has a Layer property. How do I overwrite this? Do I need to overwrite it?

I also tried it with

public CAGradientLayer layer { [Export ("Layer")] get; [Export ("Layer:")] set; }

but the app crashes (System.Reflection.TargetInvocationException – NullReferenceException when dequeuing the cell) if I want to set the colors of the layer. Furthermore it should be readonly.

Then I saw in the documentation how it could be converted:

public class BlueView : UIView
    [Export ("layerClass")]
    public static Class GetLayerClass ()
        return new Class (typeof (BlueLayer));

    public override void Draw (RectangleF rect)
        // Do nothing, the Layer will do all the drawing

public class BlueLayer : CALayer
    public override void DrawInContext (CGContext ctx)
        ctx.SetFillColor (0, 0, 1, 1);
        ctx.FillRect (Bounds);

This doesn’t help me because I need something like SetFillColors so that I can use CGColor[] array. But there is no such function.

How do I create my UIView with my custom CAGradientLayer in C# with Monotouch?


This wonderful post (iOS Programming Recipe 20: Using CAGradientLayer In A Custom View) pointed me in the right direction:

using System;
using System.Drawing;
using MonoTouch.Foundation;
using MonoTouch.UIKit;
using MonoTouch.CoreAnimation;
using MonoTouch.CoreGraphics;
using MonoTouch.ObjCRuntime;

namespace SampleApp
    public class GradientView : UIView
//      public new CAGradientLayer Layer { get; private set; }
        private CAGradientLayer gradientLayer {
            get { return (CAGradientLayer)this.Layer; }

        public GradientView ()

        [Export ("layerClass")]
        public static Class LayerClass ()
            return new Class (typeof(CAGradientLayer));

        public void setColors(CGColor[] colors){
            this.gradientLayer.Colors = colors;

//      public override void Draw (RectangleF rect)
//      {
//          // Do nothing, the Layer will do all the drawing
//      }

And here I create and set up my background view:

GradientView background = new GradientView ();
background.setColors (new CGColor[] {
    UIColor.FromRGB (18,200,45).CGColor,

Now it seems to work. Using a custom property (inclusive cast) and a separate method did the trick. Of course you can write a full accessor. This was a simple test.

Answered By – testing

Answer Checked By – Timothy Miller (Easybugfix Admin)

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