从内部SoundEffectInstance继承，未定义构造函数

Question

I'm trying to create a new class FadableSoundEffectInstance , that inherits from SoundEffectInstance .

My FadableSoundEffectInsance will allow SoundEffectInstances to be easlily faded in and out, however after finishing the class, I was rewarded with this lovely error here:

The type 'Microsoft.Xna.Framework.Audio.SoundEffectInstance' has no constructors defined

After a while of research and digging into the XNA source, I found this.

internal SoundEffectInstance(SoundEffect parentEffect, bool fireAndForget)
{
...
}

So it does have a constructor, but I cannot access it.

How can I work around this to be able to create my class?

Note for people who have not used XNA before, you DO NOT create a new class with blah = new SoundEffectInstance instead you load a SoundEffect and use the method CreateInstance() . Also, SoundEffect is a sealed class. Also, adding a constructor to my new class will throw the same error, but for SoundEffectInstance instead.

Here is my relevant code incase you need to look in depth

FadableSoundEffectInstance

    public sealed class FadableSoundEffectInstance : SoundEffectInstance
    {
        public float FadeSpeed = .01f;
        public AudioFadeState FadeState = AudioFadeState.Normal;

        public void FadeOut()
        {
            //Logic
        }
        public void FadeIn()
        {
            //Logic
        }
        public void Update(GameTime gameTime)
        {
            //Logic
        }
    }

And an extension method so I can call SoundEffect.CreateFadableInstance()

    public static FadableSoundEffectInstance CreateFadableInstance(this SoundEffect soundEffect)
    {
        return (FadableSoundEffectInstance)soundEffect.CreateInstance();
    }

Answer 1

Your question is not unique.
You don't have access to the constructor, so you can't create a derived class. This is the same whether you use XNA or not.

If you want to use your new sound effect directly, you can create a pseudo-decorator, that takes in the actual SoundEffectInstance and wraps it.

However, this doesn't help you if you want to pass your sound effect to XNA methods that want a SoundEffectInstance .

Answer 2

I solved this by adding a SoundEffectInstance to the class instead of inheriting it, it's probably not the most elegant solution, but it works.

public SoundEffectInstance BaseInstance;

And changing my extension method to this:

    public static FadableSoundEffectInstance CreateFadableInstance(this SoundEffect soundEffect)
    {
        return new FadableSoundEffectInstance(soundEffect);
    }

And my class to handle the sound effect, turn it into a SoundEffectInstance , and do any initialization the class may need

    public FadableSoundEffectInstance(SoundEffect soundEffect, float fadeSpeed = .1f)
    {
        BaseInstance = soundEffect.CreateInstance();
        BaseInstance.Volume = 0;
        FadeSpeed = fadeSpeed;
    }