如何解决无法从密封类继承的问题? [英] How to workaround impossible inheritance from sealed class?

问题描述

今天我正在WPF中工作.

Today im working in WPF.

我试图从System.Windows.Shapes.Line类继承，像这样:

I tried to inherit from System.Windows.Shapes.Line class, like this:

class MyLine : System.Windows.Shapes.Line
{
    public Ln()
    {
        this.Stroke = Brushes.Black;
    }
}

我刚刚意识到Line类是密封的.

I just realized, that Line class is sealed.

我的目标是创建一个类，该类的工作方式类似于Line类(将其放置在Canvas上)，但是我不想每次都在其上添加画笔来弄乱我的代码，可以说总是想要黑色画笔/笔触，宽度为2px.

My goal is to create a class, that will work like Line class (to put it on Canvas), but I don't want to mess my code with adding brush to it everytime, lets say always want black brush/stroke with 2px width.

我觉得我想做错事.

我应该怎么做?

推荐答案

您可以创建工厂类:

public class LineFactory
{
    public Line Create(<parameters here>)
    {
        //create and return a Line object
    }
}

工厂也可以是static，但这可能会影响可测试性.

The factory could also be static, but that could hinder testability.

请注意，此解决方案不允许您像继承那样扩展 Line类.为此，您需要返回一个MyLine类，该类将嵌入Line对象以及您希望MyLine具有的其他属性.

Note that this solution doesn't let you extend the Line class as inheritance would. To do that you would need to return a MyLine class which would embed a Line object along with the additional properties you'd want MyLine to have.

public class MyLine
{
    private Line _theBoringOriginal; // composition: "has-a" (vs inheritance "is-a")
    public MyLine(Line line)
    {
        _theBoringOriginal = line;
    }

    public foo SomeProperty { get; set; }
}

如果只是要扩展Line类的方法，则不需要新的类，则可以在静态类中编写扩展方法:

If it's just methods you want to extend the Line class with, you don't need a new class, you could just write extension methods in a static class:

public static foo DoSomethingCool(this Line line, <parameters here>)
{
    // whatever
}

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