c# - 如何在 C# 中处理组合类

Question

我在问一个关于设计模式的问题。我有一个 IDrawing 接口(interface)，以及实现此接口(interface)的两个名为 TextDrawing 和 ShapeDrawing 的类。我还有一个 View 类，它知道如何绘制这些类。但是，我有更复杂的绘图类，它们也实现了 IDrawing 接口(interface)，但由其他几个 IDrawing 类组成。

我不确定如何在我的 View 类中绘制这些复杂的类。我不想教 View 类如何绘制每个新的 IDrawing 类，因为这不是一个好的设计。我还有哪些其他选择？我的设计是否不正确，如果是这样，我如何告诉 View 的 Draw 方法了解复杂类的原始部分并绘制它们？这是我的代码:

   public interface IDrawing
   {
   }

   public class TextDrawing : IDrawing
   {
   }

   public class ShapeDrawing : IDrawing
   {      
   }

   public class SignDrawing : IDrawing
   {
      public TextDrawing Text { get; set; }
      public ShapeDrawing Border { get; set; }
   }

   public class MoreComplexDrawing : IDrawing
   {
      public TextDrawing Text { get; set; }
      public ShapeDrawing Border1 { get; set; }
      public ShapeDrawing Border2 { get; set; }
   }

   public class View
   {
      public void Draw(IDrawing drawing)
      {
           // The View only knows how to draw TextDrawing and ShapeDrawing.
           // These as the primitive building blocks of all drawings.
           // How can it draw the more complex ones!
           if (drawing is TextDrawing)
           {
              // draw it
           }
           else if (drawing is ShapeDrawing)
           {
              // draw it
           }
           else
           {
              // extract the drawings primitive parts (TextDrawing and ShapeDrawing) and draw them!
           }
      }
   }

更新:

我收到了在我的绘图类中实现 Draw() 方法的建议，但如果我这样做，它们将不再通用。例如，我将无法在我有不同绘图策略的其他项目中使用它们。有没有办法让我的设计更加灵活并保持其通用性？

Answer 1

我会向接口(interface)添加一个 Draw() 方法，并在您的每个类中实现它。

这样做的好处是您的 View 不关心实际类型是什么。

public interface IDrawing
{
    void Draw();
}

public class TextDrawing : IDrawing
{
    public void Draw()
    {
        // Draw a TextDrawing
    }
}

public class ShapeDrawing : IDrawing
{      
    public void Draw()
    {
        // Draw a ShapeDrawing
    }
}

public class SignDrawing : IDrawing
{
    public TextDrawing Text { get; set; }
    public ShapeDrawing Border { get; set; }

    public void Draw()
    {
        // Draw a SignDrawing
    }
}

public class MoreComplexDrawing : IDrawing
{
    public TextDrawing Text { get; set; }
    public ShapeDrawing Border1 { get; set; }
    public ShapeDrawing Border2 { get; set; }

    public void Draw()
    {
        // Draw a MoreComplexDrawing
    }
}

public class View
{
    public void Draw(IDrawing drawing)
    {
        //Draw the drawing
        drawing.Draw();
    }
}

更新 - 抽象掉对 SkiaSharp 的依赖

您需要为 SkiaSharp 或实际执行绘图的任何外部依赖项创建一个包装器。这应该与您的 IDrawing 接口(interface)和派生类存在于同一个程序集中。

public interface IDrawingContext
{
    // Lots of drawing methods that will facilitate the drawing of your `IDrawing`s
    void DrawText(...);
    void DrawShape(...);
    void DrawBorder(...);
}

以及SkiaSharp具体实现

public class SkiaSharpDrawingContext IDrawingContext
{
    // Lots of drawing methods that will facilitate the drawing of your IDrawings
    public void DrawText(...) { /* Drawing code here */ }
    public void DrawShape(...) { /* Drawing code here */ }
    public void DrawBorder(...) { /* Drawing code here */ }
}

更新IDrawing界面为

public interface IDrawing
{
    void Draw(IDrawingContext drawingContext);
}

也更新您的类(class)以反射(reflect)这一变化。您的类将调用 IDrawingContext 实现上的方法来进行绘图。

在您的应用程序中创建依赖项特定实现并更新您的 View 类以使用新的 SkiaSharpDrawingContext

public class View
{
    public void Draw(IDrawing drawing)
    {
        // This should ideally be injected using an IOC framework
        var drawingContext = new SkiaSharpDrawingContext(...);

        //Draw the drawing
        drawing.Draw(drawingContext);
    }
}