是否可以阻止对类的成员变量的某些方法调用

Question

I require to create a Camera class on top of the default camera class for Windows Phone 8, PhotoCaptureDevice

Ideally I would have wanted to build a child class

class CustomCaptureDevice:PhotoCaptureDevice{
    ....
    ....
}

This would have allowed me to both configure the camera device, and also provide for some additional frame processing technique via CustomCaptureDevice. Unfortunately, PhotoCaptureDevice is a sealed class , hence I cannot do that.

Now I can think of two alternative methods which could help me tackle the problem:

(1)

class CustomCaptureDevice
{
    private PhotoCaptureDevice captureDevice;

    // Implement all the functions of PhotoCaptureDevice here. And internally redirect them to PhotoCaptureDevice

}

The above method would be too cumbersome. And in case of any API changes to PhotoCaptureDevice, could require significant updates to CustomCaptureDevice class.

(2)

class CustomCaptureDevice
{
    public PhotoCaptureDevice captureDevice;

    // Expose this variable to the user, who can set things in PhotoCaptureDevice as per his needs.

}

The above seems to be an easier solution, since it would require minimal updates in case of API changes to PhotoCaptureDevice.

It seems (2) could fit my requirement well. But I have an additional requirement, because of which (2) could prove unfit. I want to disable certain configuration capabilities in PhotoCaptureDevice, since I want to keep a few parameters like exposure and focus not configurable by the user.

How could I accomplish this in the design framework of (2). Is it possible at all?

I understand that it would be easy to implement by approach (1). Please take note of the constraint that PhotoCaptureDevice is a sealed class .

Answer 1

The first approach is usually called the decorator pattern (ie a wrapper). I believe that this is exactly the thing you need, as it allows you to provide any functionality for the given interface under the hood.

To make the class interchangeable with a PhotoCaptureDevice in other parts of your app, you will have to implement its relevant interfaces:

public class ExtendedPhotoCaptureDevice : IDisposable, ICameraCaptureDevice
{
    private readonly ICameraCaptureDevice _actualImplementation;
    ...
}