C#:将派生类作为一个泛型参数传递 [英] C#:Passing derived classes as one generic parameter

问题描述

我最近开始更多地了解事件/委托以及课程的扩展.

I recently started learning more about events/delegates in conjunction with extensions to a class.

我想通过向 Windows 窗体控件添加一个名为 SetDraggable() 的扩展方法来将我学到的知识付诸实践，该方法又使用了一个 MouseDown 和 MouseMove 事件来移动控件.

I wanted to put what I learned into practice by adding an extension method to Windows Form controls called SetDraggable(), which in turn uses a MouseDown and MouseMove events to move the control around.

一切正常，除了它只适用于特定控件的想法——在我的例子中，是一个 Button.

All works fine, except for the idea that it only applies to a specific control -- in my case, a Button.

namespace Form_Extensions
{
    public static class Extensions
    {
        private static System.Windows.Forms.Button StubButton;
        private static Point MouseDownLocation;
        public static void SetDraggable(this System.Windows.Forms.Button b)
        {
            b.MouseDown += b_MouseDown;
            b.MouseMove += b_MouseMove;
            StubButton = b;
        }

        private static void b_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
        {
            if (e.Button == System.Windows.Forms.MouseButtons.Left)
            {
                MouseDownLocation = e.Location;
            }
        }

        static void b_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
        {
            if (e.Button == System.Windows.Forms.MouseButtons.Left)
            {
                StubButton.Left = e.X + StubButton.Left - MouseDownLocation.X;
                StubButton.Top = e.Y + StubButton.Top - MouseDownLocation.Y;
            }
        }

    }
}

可以看出，我需要特定的控件来调用鼠标事件——我无法从 父 类 System.Windows.Forms 访问这些事件.

As can be seen, I need the specific control in order to call the Mouse events -- I cannot access those events from the parent class System.Windows.Forms.

所以我的问题仍然存在 -- 是否有一个概念允许程序员一般地将所有派生类作为参数传递.我基本上是试图避免为每个控件复制粘贴以下代码，并希望将其概括为从 System.Windows.Forms 派生的所有类.

So my question remains -- is there a concept that allows programmers to generically pass all derived classes as an argument. I am basically trying to avoid copy pasting the below code for every single control and would like to generalize it for all classes derived from System.Windows.Forms.

据我所知，这个想法的主要缺陷是我假设所有派生类都会有我需要的事件；然而，由于委托形式的函数也存在类似的情况，我希望有人可以权衡涉及对象或参数的情况.

As far as I can tell, the main flaw in that idea is the fact that I am ASSUMING that all derived classes will have the event I need; however, since a similar thing exists for functions in the form of Delegates, I was hoping someone could weigh in for cases involving objects or parameters.

推荐答案

父类不是 System.Windows.Forms，那只是命名空间.实际的父类是 Control，你当然可以使用它:) 使用泛型方法也是可能的，但不是真正必要的.

The parent class isn't System.Windows.Forms, that's just the namespace. The actual parent class is Control, and you can certainly use that :) Using a generic method is also possible, but not really necessary.

理想情况下，您还希望避免使用那些静态字段，因为可能有多个并发可拖动对象；SetControlDraggable 方法中的闭包效果会更好:

Ideally, you'd also want to avoid those static fields, since it's possible to have multiple concurrent draggables; a closure in the SetControlDraggable method will work a lot better:

public static void SetControlDraggable(this Control control)
{
  Point mouseDownLocation = Point.Empty;

  control.MouseDown += (s, e) =>
    {
      if (e.Button == MouseButtons.Left) mouseDownLocation = e.Location;
    }
  control.MouseUp += (s, e) =>
    {
      if (e.Button == MouseButtons.Left)
      {
        control.Left = e.X + control.Left - mouseDownLocation.X;
        control.Top = e.Y + control.Top - mouseDownLocation.Y;
      }
    }
}

这篇关于C#:将派生类作为一个泛型参数传递的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！