ios - 在 iOS 中捕获签名时出现性能问题

Question

我有一个签名控件，效果很好，除非你的名字很长，然后它开始显示空白。似乎与性能有关，但在模拟器和最新的 iPad 上都是一样的。我在下面附上了一个示例项目以及签名绘图代码。

如有任何帮助，我们将不胜感激!

https://dl.dropboxusercontent.com/u/25670071/SignatureArchive.zip

 using System;
 using MonoTouch.UIKit;
 using MonoTouch.CoreGraphics;
 using System.Drawing;

namespace MyApp
{
  public class SignatureViewV2 : UIView
  {     
    public delegate void SignatureChanged();
    public SignatureChanged OnSignatureChanged;

    private bool _empty = true;
    // clear the canvas
    public void Clear ()
    {
        drawPath.Dispose ();
        drawPath = new CGPath ();
        fingerDraw = false;
        SetNeedsDisplay ();
        _empty = true;
    }

    public bool IsEmpty ()
    {
        return _empty;
    }

    public SignatureViewV2 (RectangleF frame) : base(frame)
    {

        this.drawPath = new CGPath ();
        this.BackgroundColor = UIColor.White;

    }


    private PointF touchLocation;
    private PointF prevTouchLocation;
    private CGPath drawPath;
    private bool fingerDraw;

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

        UITouch touch = touches.AnyObject as UITouch;
        this.fingerDraw = true;
        this.touchLocation = touch.LocationInView (this);
        this.prevTouchLocation = touch.PreviousLocationInView (this);
        this.SetNeedsDisplay ();

    }

    public override void Draw (RectangleF rect)
    {
        base.Draw (rect);

        if (this.fingerDraw) {
            using (CGContext context = UIGraphics.GetCurrentContext()) {
                context.SetStrokeColor (UIColor.FromRGB(63, 112, 185).CGColor);
                context.SetLineWidth (2f);
                context.SetLineJoin (CGLineJoin.Round);
                context.SetLineCap (CGLineCap.Round);
                this.drawPath.MoveToPoint (this.prevTouchLocation);
                this.drawPath.AddLineToPoint (this.touchLocation);
                context.AddPath (this.drawPath);
                context.DrawPath (CGPathDrawingMode.Stroke);
            }
            if(OnSignatureChanged != null)
                OnSignatureChanged();
            _empty = false;
        }    
    }

    public override void TouchesMoved (MonoTouch.Foundation.NSSet touches, UIEvent evt)
    {
        base.TouchesMoved (touches, evt);

        UITouch touch = touches.AnyObject as UITouch;
        this.touchLocation = touch.LocationInView (this);
        this.prevTouchLocation = touch.PreviousLocationInView (this);
        this.SetNeedsDisplay ();
    }

    public UIImage GetDrawingImage ()
    {
        UIImage returnImg = null;

        UIGraphics.BeginImageContext (this.Bounds.Size);

        using (CGContext context = UIGraphics.GetCurrentContext()) {
            context.SetStrokeColor (UIColor.FromRGB(63, 112, 185).CGColor);
            context.SetLineWidth (5f);
            context.SetLineJoin (CGLineJoin.Round);
            context.SetLineCap (CGLineCap.Round);
            context.AddPath (this.drawPath);
            context.DrawPath (CGPathDrawingMode.Stroke);
            returnImg = UIGraphics.GetImageFromCurrentImageContext ();
        }

        UIGraphics.EndImageContext ();

        return returnImg;
    }



}

Answer 1

你不能依赖 Draw()被称为每个TouchesMoved() .如果Draw()每 2 次触摸被调用一次，你会得到所描述的间隙。

我会通过排队(例如在 Queue<T> 中)TouchesMoved() 中的触摸来解决这个问题并在 Draw() 中出队

您可能还有另一个问题:在每个 Draw() ，您每次都将完整路径重新添加到当前路径。您可能只需调用 AddPath 即可解决此问题对于新的分割市场或调用 AddPath()一次，将段添加到您的路径(`Move，AddLine)并重新绘制它。但我还没有测试过这些。