UI上的Xamarin.iOS手指画

Question

我想用Xamarin iOS在UIImageView-Control上用一根手指画画。 我找到了什么： First Second

这两个示例无法正常工作，因为第一个链接存在以下问题：

1. 我必须用两根手指画画，但我只想用一只手指（不要与图片混淆，我必须用两根手指来激活触控功能）
2. 定位错误我猜这些问题依赖于错误的缩放（参见附图）



















这是我目前的代码：

public partial class DetailImageView : UIImageView
{
    DetailImageViewController ctrl;
    public DetailImageView (IntPtr handle) : base (handle)
    {

    }

    public void Initialize(DetailImageViewController rootController)
    {
        ctrl = rootController;
    }

    public override void TouchesBegan(NSSet touches, UIEvent evt)
    {
        base.TouchesBegan(touches, evt);

        UITouch touch = touches.AnyObject as UITouch;

        drawOnTouch(touch);

        //DrawLineOnImage();
    }

    public override void TouchesMoved(NSSet touches, UIEvent evt)
    {
        base.TouchesMoved(touches, evt);
        UITouch touch = touches.AnyObject as UITouch;

        drawOnTouch(touch);

        //DrawLineOnImage();
    }


    private void drawOnTouch(object data)
    {

        UITouch touch = data as UITouch;

        if (null != touch)
        {

            UIGraphics.BeginImageContext(this.Image == null ? this.Frame.Size : this.Image.Size);

            //UIGraphics.BeginImageContext(this.Frame.Size);

            using (CoreGraphics.CGContext cont = UIGraphics.GetCurrentContext())
            {

                if (this.Image != null)
                {

                    cont.TranslateCTM(0f, this.Image.Size.Height);
                    cont.ScaleCTM(1.0f, -1.0f);
                    cont.DrawImage(new RectangleF(0f, 0f, Convert.ToSingle(this.Image.Size.Width)
                                                  , Convert.ToSingle(this.Image.Size.Height)), this.Image.CGImage);
                    cont.ScaleCTM(1.0f, -1.0f);
                    cont.TranslateCTM(0f, -this.Image.Size.Height);


                } //end if

                CGPoint lastLocation = touch.PreviousLocationInView(this);
                CGPoint pt = touch.LocationInView(this);
                using (CGPath path = new CGPath())
                {

                    cont.SetLineCap(CGLineCap.Round);
                    cont.SetLineWidth(10);
                    cont.SetStrokeColor(0, 2, 3, 1);

                    var xMultiplier = Image.Size.Height / Frame.Height;
                    var yMultiplier = Image.Size.Width / Frame.Width;

                    var xLoc = lastLocation.X * xMultiplier;
                    var yLoc = lastLocation.Y * yMultiplier;

                    path.MoveToPoint(xLoc, yLoc);
                    path.AddLines(new CGPoint[] { new CGPoint(xLoc,
                                                              yLoc),
                        new CGPoint(pt.X * xMultiplier, pt.Y * yMultiplier) });
                    path.CloseSubpath();

                    cont.AddPath(path);
                    cont.DrawPath(CGPathDrawingMode.FillStroke);
                    this.Image = UIGraphics.GetImageFromCurrentImageContext();

                }//end using path


            }//end using cont
            UIGraphics.EndImageContext();
            this.SetNeedsDisplay();

        }//end if
    }//end void drawOnTouch
}

Answer 1

  

定位错误我认为问题依赖于错误   缩放

因为当我们使用图片时，图片的大小通常与UIImageView的大小不同。您使用图像的大小来绘制路径，因此它会错过它的位置。尝试修改如下：

if (null != touch)
{

    UIGraphics.BeginImageContext(this.Frame.Size);

    using (CoreGraphics.CGContext cont = UIGraphics.GetCurrentContext())
    {

        if (this.Image != null)
        {

            cont.TranslateCTM(0f, this.Frame.Size.Height);
            cont.ScaleCTM(1.0f, -1.0f);
            cont.DrawImage(new RectangleF(0f, 0f, Convert.ToSingle(this.Frame.Size.Width)
                                            , Convert.ToSingle(this.Frame.Size.Height)), this.Image.CGImage);
            cont.ScaleCTM(1.0f, -1.0f);
            cont.TranslateCTM(0f, -this.Frame.Size.Height);


        } //end if

        CGPoint lastLocation = touch.PreviousLocationInView(this);
        CGPoint pt = touch.LocationInView(this);
        using (CGPath path = new CGPath())
        {

            cont.SetLineCap(CGLineCap.Round);
            cont.SetLineWidth(10);
            cont.SetStrokeColor(0, 2, 3, 1);

            var xLoc = lastLocation.X;
            var yLoc = lastLocation.Y;

            path.MoveToPoint(xLoc, yLoc);
            path.AddLines(new CGPoint[] { new CGPoint(xLoc,
                                                    yLoc),
            new CGPoint(pt.X, pt.Y) });
            path.CloseSubpath();

            cont.AddPath(path);
            cont.DrawPath(CGPathDrawingMode.FillStroke);
            this.Image = UIGraphics.GetImageFromCurrentImageContext();

        }//end using path


    }//end using cont
    UIGraphics.EndImageContext();
    this.SetNeedsDisplay();

}//end if

关于

  

我必须用两根手指画画，但我只想用一根   手指

你是什么意思？代码可以用于仅用手指绘制路径。