c# - TouchMove 事件在 xamarin ios 中结束得如此之快

Question

我创建了一个如下所示的 Canvas View 。当我将它应用到新项目时，它可以正常工作，但是当我将它放入我的真实项目时，我无法绘制实线。它总是被虚线(如下图所示)。第一次，我认为这是一个问题，因为我推了太多屏幕，直到出现这个可绘制对象。但每次我插入新 View 时，我都尝试禁用前一个 View 的 UserInteraction，但它不起作用。请帮忙!

public class CanvasView : UIView
{
    public CanvasView (CGRect frame) : base(frame)
    {
        this.drawPath = new CGPath();
        BackgroundColor = UIColor.White;

    }


    private CGPoint touchLocation;
    private CGPoint previousTouchLocation;
    private CGPath drawPath;
    private bool fingerDraw;
    public override void LayoutSubviews ()
    {
        base.LayoutSubviews ();
        Layer.BorderWidth = 0.5f;
        Layer.BorderColor = UIColor.FromRGB (146, 146, 146).CGColor;
    }
    public override void TouchesBegan (NSSet touches, UIEvent evt)
    {
        base.TouchesBegan (touches, evt);
        UITouch touch = touches.AnyObject as UITouch;
        this.fingerDraw = true;
        this.touchLocation = touch.LocationInView(this);
        this.previousTouchLocation = touch.PreviousLocationInView(this);

        this.SetNeedsDisplay();
    }
    public override void TouchesMoved (NSSet touches, UIEvent evt)
    {
        base.TouchesMoved (touches, evt);
        UITouch touch = touches.AnyObject as UITouch;
        this.touchLocation = touch.LocationInView(this);
        this.previousTouchLocation = touch.PreviousLocationInView(this);

        this.SetNeedsDisplay();
    }

    public override void TouchesEnded (NSSet touches, UIEvent evt)
    {
        base.TouchesEnded (touches, evt);
        var alert = new UIAlertView () {
            Message = "Xui"
        };
        alert.AddButton("OK");
        alert.Show();
    }
    public override void Draw (CGRect rect)
    {
        base.Draw (rect);
        if (this.fingerDraw)
        {
            using (CGContext context = UIGraphics.GetCurrentContext())
            {
                context.SetStrokeColor(UIColor.Black.CGColor);
                context.SetLineWidth(1.5f);
                context.SetLineJoin(CGLineJoin.Round);
                context.SetLineCap(CGLineCap.Round);
                this.drawPath.MoveToPoint(this.previousTouchLocation);
                this.drawPath.AddLineToPoint(this.touchLocation);
                context.AddPath(this.drawPath);
                context.DrawPath(CGPathDrawingMode.Stroke);
            }
        }
    }
}

the screen

Answer 1

我认为问题不在于 TouchesMoved，而在于您的绘图逻辑。当您调用 SetNeedsDisplay() 时，它并不意味着“立即绘制”，它的意思是“我有需要绘制的更改，所以请亲爱的，尽可能绘制我。”这意味着在处理绘图之前，会有更多的触摸进来。

您必须保持前一个点相同，直到调用 Draw 为止，或者您必须将这些点放入缓冲区并同时绘制它们。我会做第一个，因为它更简单。