Question

I give up now on this very simple test I’ve been trying to run. I want to add a subview to my window which does nothing but draw a line from one corner of the iPhone’s screen to the other and then, using touchesMoved() it is supposed to draw a line from the last to the current point.
The issues:
1. Already the initial line is not visible.
2. When using Interface Builder, the initial line is visible, but drawRect() is never called, even if I call SetNeedsDisplay().

It can’t be that hard…can somebody fix the code below to make it work?

In main.cs in FinishedLaunching():

oView = new TestView();
oView.AutoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleHeight;
oView.Frame = new System.Drawing.RectangleF(0, 0, 320, 480);
window.AddSubview(oView);
window.MakeKeyAndVisible ();

The TestView.cs:

using System;
using MonoTouch.UIKit;
using MonoTouch.CoreGraphics;
using System.Drawing;
using MonoTouch.CoreAnimation;
using MonoTouch.Foundation;
namespace Test
{
    public class TestView : UIView
    {
        public TestView () : base()
        {
        }

        public override void DrawRect (RectangleF area, UIViewPrintFormatter formatter)
        {
            CGContext oContext = UIGraphics.GetCurrentContext();
            oContext.SetStrokeColor(UIColor.Red.CGColor.Components);
            oContext.SetLineWidth(3.0f);
            this.oLastPoint.Y = UIScreen.MainScreen.ApplicationFrame.Size.Height - this.oLastPoint.Y;
            this.oCurrentPoint.Y = UIScreen.MainScreen.ApplicationFrame.Size.Height - this.oCurrentPoint.Y;
            oContext.StrokeLineSegments(new PointF[] {this.oLastPoint, this.oCurrentPoint });
            oContext.Flush();
            oContext.RestoreState();
            Console.Out.WriteLine("Current X: {0}, Y: {1}", oCurrentPoint.X.ToString(), oCurrentPoint.Y.ToString());
            Console.Out.WriteLine("Last X: {0}, Y: {1}", oLastPoint.X.ToString(), oLastPoint.Y.ToString());

        }

        private PointF oCurrentPoint = new PointF(0, 0);
        private PointF oLastPoint = new PointF(320, 480);

        public override void TouchesMoved (MonoTouch.Foundation.NSSet touches, UIEvent evt)
        {
            base.TouchesMoved (touches, evt);
            UITouch oTouch = (UITouch)touches.AnyObject;
            this.oCurrentPoint = oTouch.LocationInView(this);
            this.oLastPoint = oTouch.PreviousLocationInView(this);
            this.SetNeedsDisplay();
        }
    }
}

Answer 1

You overrode the wrong Draw method.

You overrode DrawRect (RectangleF, UIViewPrintFormatter) which is used for printing.

You want to override Draw (RectangleF)