用CAGradientLayer作爲後備存儲在UIView上畫線

Question

我創建了一個UIView子類，它的圖層使用CAGradientLayer。這工作正常。現在我想在漸變的末尾繪製一條線（用作分隔符）。我以爲我可以使用這個方法drawRect：

public class GradientView : UIView 
{ 
    // accessors 
    private CAGradientLayer gradientLayer { 
     // read-only 
     get { return (CAGradientLayer)this.Layer; } 
    } 

    public CGColor[] Colors { 
     // set the colors of the gradient layer 
     get { return this.gradientLayer.Colors; } 
     set { this.gradientLayer.Colors = value; } 
    } 

    [Export ("layerClass")] 
    public static Class LayerClass() 
    { 
     // use a different Core Animation layer for its backing store 
     // normally a CALayer is used for a UIView 
     return new Class (typeof(CAGradientLayer)); 
    } 

    public override void Draw (RectangleF rect) 
    { 

     PointF pointA = new PointF (0, rect.Height); 
     PointF pointB = new PointF (rect.Width, rect.Height); 
     CAShapeLayer line = new CAShapeLayer(); 
     UIBezierPath linePath = new UIBezierPath(); 
     linePath.MoveTo (pointA); 
     linePath.AddLineTo(pointB); 
     line.Path = linePath.CGPath; 
     line.FillColor = null; 
     line.Opacity = 1.0f; 
     line.StrokeColor = UIColor.Black.CGColor; 

     this.gradientLayer.AddSublayer (line); 

     base.Draw (rect); 
    } 
} 

但我得到一個黑色的背景。我可以使用drawRect嗎？或者我如何在其上添加一行？

我使用C＃作爲語言，但您也可以在Objective-C中提供您的解決方案。自動佈局確定GradientView的大小，我的舊解決方案也適應方向更改。

編輯：

我試了一下西里爾說：

public class GradientView : UIView 
{ 
    // accessors 
    private CAShapeLayer line; 

    private CAGradientLayer gradientLayer { 
     // read-only 
     get { return (CAGradientLayer)this.Layer; } 
    } 

    public CGColor[] Colors { 
     // set the colors of the gradient layer 
     get { return this.gradientLayer.Colors; } 
     set { this.gradientLayer.Colors = value; } 
    } 

    public GradientView() 
    { 
     PointF pointA = new PointF (0, this.Bounds.Height); 
     PointF pointB = new PointF (this.Bounds.Width, this.Bounds.Height); 
     line = new CAShapeLayer(); 
     UIBezierPath linePath = new UIBezierPath(); 
     linePath.MoveTo (pointA); 
     linePath.AddLineTo(pointB); 
     line.Path = linePath.CGPath; 
     line.FillColor = null; 
     line.Opacity = 1.0f; 
     line.StrokeColor = UIColor.Black.CGColor; 
     line.LineWidth = 1.0f; 

     this.gradientLayer.AddSublayer (line); 
    } 

    [Export ("layerClass")] 
    public static Class LayerClass() 
    { 
     // use a different Core Animation layer for its backing store 
     // normally a CALayer is used for a UIView 
     return new Class (typeof(CAGradientLayer)); 
    } 

    public override void LayoutSubviews() 
    { 
     PointF pointA = new PointF (0, this.Bounds.Height-2); 
     PointF pointB = new PointF (this.Bounds.Width, this.Bounds.Height-2); 
     UIBezierPath linePath = new UIBezierPath(); 
     linePath.MoveTo (pointA); 
     linePath.AddLineTo(pointB); 

     line.Path = linePath.CGPath; 

     base.LayoutSubviews(); 
    } 
} 

這似乎做我想做的只是行不薄的髮際線。是CAShapeLayer不適合這個嗎？

解決方案：

當然有可能使用CAShapeLayer，但如果我必須設置事情drawRect，然後我徹底劃清我行那裏。現在對我來說，解決方案看起來像下面這樣：

public class GradientView : UIView 
{ 
    // accessors 
    private CAShapeLayer line; 

    private CAGradientLayer gradientLayer { 
     // read-only 
     get { return (CAGradientLayer)this.Layer; } 
    } 

    public CGColor[] Colors { 
     // set the colors of the gradient layer 
     get { return this.gradientLayer.Colors; } 
     set { this.gradientLayer.Colors = value; } 
    } 

    public GradientView() 
    { 
     this.BackgroundColor = UIColor.Clear; 
    } 

    [Export ("layerClass")] 
    public static Class LayerClass() 
    { 
     // use a different Core Animation layer for its backing store 
     // normally a CALayer is used for a UIView 
     return new Class (typeof(CAGradientLayer)); 
    } 

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

     // get graphics context 
     CGContext context = UIGraphics.GetCurrentContext(); 

     // start point 
     context.MoveTo (0, rect.Height); 

     // end point 
     context.AddLineToPoint (rect.Width, rect.Height); 

     context.SetLineWidth (1.0f); 

     context.SetShouldAntialias(false); 

     // draw the path 
     context.DrawPath (CGPathDrawingMode.Stroke); 
    } 

Answer 1

使用您的視圖的CAGradientLayer作爲襯裏層不會阻止你加入另一個CAShapeLayer在初始化您的視圖中。然後，您可以使用此形狀圖層繪製直線，方法是相應地設置其path屬性（並在任何時候邊界發生更改時重新計算它，-layoutSubviews以對方向/佈局更改作出正確反應）。