如何在C#中获得更多的封装？

发布于 2024-12-06 14:21:21 字数 455 浏览 1 评论 0原文

我最近大约完全学习了 C#。然而，在 C++ 中，当将对象传递给方法时，我可以使用 const 修饰符实现更好的封装。但在C#中，可以通过引用参数修改对象，例如Graphics对象上的Dispose。

有时我需要更多的封装。属性可以给出更好的解决方案。但是，我发现，例如，不允许修改 Form.Location 属性甚至其 X 成员。虽然 Form.Location 是 get; set; 属性，其成员不能修改。我尝试用 Point {get; 来做到这一点set;} 属性，但我仍然可以修改 X 成员。

正如前面提到的，当诸如 Dispose 之类的方法是对象时，这也是一个问题。

如何在C#中实现更多的封装？

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笙痞 2024-12-13 14:21:21

您不能使用 Form.Location 的 X 属性，因为 Form.Location 是返回值类型的属性（点）。一旦您访问 Form.Location，您就会获得该位置的副本；因此，更改此副本中的某些内容是没有意义的。由于 this.Location.X = ... 是一个明显的错误，C# 编译器会阻止您这样做。

但是，您可以替换 Form.Location 的完整值，因为它的属性设置器是 public：

private void button1_Click(object sender, EventArgs e)
{
    // move window to the left edge of the screen
    this.Location = new Point(0, this.Location.Y);    
}

或者，

private void button1_Click(object sender, EventArgs e)
{
    // move window to the left edge of the screen
    var loc = this.Location;
    loc.X = 0;               // yes, it's a mutable struct
    this.Location = loc;
}

回到您原来的问题：如果您愿意要使对象可访问，但不希望它被修改，您需要自己封装它。例如，如果您希望类的使用者能够在 Graphics 对象上进行 Draw，但不希望他们调用 Dispose，只是无法直接公开 Graphics 对象。相反，您需要包装允许消费者调用的每个方法：

// bad, consumer can do anything with the Graphics object
public Graphics Graphics
{
    get { return graphics; }
}

// good, consumer can only do specific stuff
public void Draw(...)
{
    graphics.Draw(...);
}

You cannot the X property of Form.Location, because Form.Location is a property that returns a value type (Point). As soon as you access Form.Location, you get a copy of the location; thus, changing something in this copy is meaningless. Since this.Location.X = ... is an obvious mistake, the C# compiler prevents you from doing it.

You can, however, replace the complete value of Form.Location, since its property setter is public:

private void button1_Click(object sender, EventArgs e)
{
    // move window to the left edge of the screen
    this.Location = new Point(0, this.Location.Y);    
}

or, alternatively,

private void button1_Click(object sender, EventArgs e)
{
    // move window to the left edge of the screen
    var loc = this.Location;
    loc.X = 0;               // yes, it's a mutable struct
    this.Location = loc;
}

To get back to your original question: If you want to make an object accessible, but do not want it to be modified, you will need to encapsulate it yourself. For example, if you want the consumers of your class to be able to Draw on your Graphics object but do not want them to call Dispose, just cannot expose the Graphics object directly. Instead, you need to wrap every method that the consumer is allowed to call:

// bad, consumer can do anything with the Graphics object
public Graphics Graphics
{
    get { return graphics; }
}

// good, consumer can only do specific stuff
public void Draw(...)
{
    graphics.Draw(...);
}

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