如何在 C# 中处理组合类

Question

我问的部分与设计模式有关。

假设我有一个 IDrawing 界面。另外两个名为 TextDrawing 和 ShapeDrawing 的基本 classes 实现了这个，我有一个 View class 知道如何画这些！

但是我有更复杂的绘图 classes 也实现了 IDrawing 接口但是由几个 IDrawing class他们自己！

如何在我的 View class 中绘制这些？显然教 View class 绘制每个新的 IDrawing 不是一个好主意！但是我还有什么选择呢？也许设计不正确？我如何告诉 View 的 Draw 方法了解复杂 classes 的原始部分并绘制它们？

   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中实施 Draw() 方法的建议 classes。 View 中的 Draw 方法依赖外部库进行绘制（在我的例子中，它是 SkiaSharp 库）。如果我在这些 classes 中实现 Draw，它们将不再通用！例如，我将无法在其他项目中使用它们，在这些项目中我有不同的绘制策略。

Answer 1

您可以选择强制 classes 执行名为 Draw() 的方法。

public interface IDrawing
{
    void Draw(); 
}

现在您可以简单地调用此方法并将内部实现的责任交给 classes 自己。

public void Draw(IDrawing drawing)
{

     drawing.Draw();

例如TextDrawing将被迫实施此方法

public class TextDrawing : IDrawing
{
    public void Draw()
    {
        // draw Text-like
    }
}

在您的 View class 中，对 drawing.Draw(); 的调用将导致正确的实现。

How can I tell the View's Draw method to know the primitive parts of the complex classes and draw them?

现在在复杂的 classes 中，您只需使用简单绘图中已经实现的方法 classes

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

    public void Draw()
    {
        Text.Draw();

        Border.Draw();

        Text.Draw();
    }
}

Answer 2

我会向界面添加一个 Draw() 方法，并在您的每个 classes 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。这应该存在于与您的 IDrawing 接口相同的程序集中并派生 classes.

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 */ }
}

将 IDrawing 界面更新为

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

也在更新您的 classes 以反映这一变化。您的 classes 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 class 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);
    }
}

Answer 3

you can polymorphically draw without checking the type.

 public class View
   {
      public void Draw(IDrawing drawing)
      {
         drawing.Draw();
      }
   }
Encapsulate each drawing strategy (Strategy Pattern) in different class and you could inject each strategy via DI.

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