C＃中的OO问题

Question

class Frame
{
    static int X;
    static int Y;
    static uint Color;

    static protected bool Check()
    {
        return (Coords.GetPixelColor(X, Y) == Color);
    }
}

class frameBeginning : Frame
{
    static int X = 1;
    static int Y = 2;
    static int Color = 3;
}

frameBeginning.Check(); cannot compile, because Check() is inaccessible due to its protection level.

But why, Check() is protected?

Answer 1

This is not a problem. The behavior you are seeing is part of the definition of protected . If you want to call frameBeginning.Check from outside the code of the frameBeginning or frame class, the method needs to be public or internal .

Answer 2

Because you declared it as protected in the code shown above.

But different rules apply to static methods. Check out the SO question below:

C#: Can a base class use a derived class's variable in a static function?

Answer 3

You could call Check from within frameBeginning , but not outside the class. This is what protected means: visible to derived classes, not to external code.

Answer 4

Using frameBeginning.Check() from outside needs that Check() is public. Being protected is only visible to derived clasess, but not from outside. You're trying to access the Check() method from outside, so you need to do Check() public or internal.

In other words, you could acess Check() from a frameBeginning instance, but Check() is static, if you want to access Check() from outside, you need to change the visibility to public (or internal).

Answer 5

这样类本身和所有继承的类都可以使用该方法，独立于对象的实例，但是类之外的任何东西都不能使用该方法。

Answer 6

There are 5 access modifiers... you need to understand what kind of access you can get by each.

private - Function can only be called from within the class

protected - Function can be called only from within the class and all its derived classes

internal protected - Function can be called by the class and all its derived classes inside the Assembly

internal - Almost like public - Can be called from anywhere inside the Assembly ... Used for Incapsulation

public - Can be called from anywhere