C# XNA 4.0 textures disappearing when minimized

Question

I'm fairly new to XNA, and I've been running into some problems. Whenever I minimize the game, the screen turns black when I open it back up again. What could be the cause of this and how could it be solved?

Here's my Image class:

 public class Image
 {
    public float Alpha;
    public string Text, FontName, Path;
    public Vector2 Position, Scale;
    public Rectangle SourceRect;
    public bool IsActive;
    public bool Logo;
    public Texture2D Texture;
    Vector2 origin;
    ContentManager content;
    RenderTarget2D renderTarget;
    SpriteFont font;
    Dictionary<string, ImageEffect> effectList;
    public string Effects;

    public FadeEffect FadeEffect;

    void SetEffect<T>(ref T effect)
    {
        if (effect == null)
            effect = (T)Activator.CreateInstance(typeof(T));
        else
        {
            (effect as ImageEffect).IsActive = true;
            var obj = this;
            (effect as ImageEffect).LoadContent(ref obj);
        }

        effectList.Add(effect.GetType().ToString().Replace("RPG.", ""), (effect as ImageEffect));
    }

    public void ActivateEffect(string effect)
    {
        if (effectList.ContainsKey(effect))
        {
            effectList[effect].IsActive = true;
            var obj = this;
            effectList[effect].LoadContent(ref obj);
        }
    }

    public void DeactivateEffect(string effect)
    {
        if (effectList.ContainsKey(effect))
        {
            effectList[effect].IsActive = false;
            effectList[effect].UnloadContent();
        }
    }

    public void StoreEffects()
    {
        Effects = String.Empty;
        foreach (var effect in effectList)
        {
            if (effect.Value.IsActive)
                Effects += effect.Key + ":";
        }

        if(Effects != String.Empty)
            Effects.Remove(Effects.Length - 1);
    }

    public void RestoreEffects()
    {
        foreach (var effect in effectList)
            DeactivateEffect(effect.Key);
        string[] split = Effects.Split(':');
        foreach (string s in split)
            ActivateEffect(s);
    }

    public Image()
    {
        Path = Text = Effects = String.Empty;
        FontName = "Fonts/FixedSys Ex";
        Position = Vector2.Zero;
        Scale = Vector2.One;
        Alpha = 1.0f;
        SourceRect = Rectangle.Empty;
        effectList = new Dictionary<string, ImageEffect>();
    }

    public void LoadContent()
    {
        content = new ContentManager(ScreenManager.Instance.Content.ServiceProvider, "Content");


        if (Path != String.Empty)
            Texture = content.Load<Texture2D>(Path);

        font = content.Load<SpriteFont>(FontName);

        Vector2 dimensions = Vector2.Zero;

        if (Texture != null)
            dimensions.X += Texture.Width;
        dimensions.X += font.MeasureString(Text).X;

        if (Texture != null)
            dimensions.Y = Math.Max(Texture.Height, font.MeasureString(Text).Y);
        else
            dimensions.Y = font.MeasureString(Text).Y;

        if (SourceRect == Rectangle.Empty)
            SourceRect = new Rectangle(0, 0, (int)dimensions.X, (int)dimensions.Y);

        renderTarget = new RenderTarget2D(ScreenManager.Instance.GraphicsDevice, (int)dimensions.X, (int)dimensions.Y);
        ScreenManager.Instance.GraphicsDevice.SetRenderTarget(renderTarget);
        ScreenManager.Instance.GraphicsDevice.Clear(Color.Transparent);
        ScreenManager.Instance.SpriteBatch.Begin();
        if (Texture != null)
            ScreenManager.Instance.SpriteBatch.Draw(Texture, Vector2.Zero, Color.White);
        ScreenManager.Instance.SpriteBatch.DrawString(font, Text, Vector2.Zero, Color.White);
        ScreenManager.Instance.SpriteBatch.End();

        Texture = renderTarget;

        ScreenManager.Instance.GraphicsDevice.SetRenderTarget(null);

        SetEffect<FadeEffect>(ref FadeEffect);

        if (Effects != string.Empty)
        {
            string[] split = Effects.Split(':');
            foreach (string item in split)
                ActivateEffect(item);
        }


    }

    public void UnloadContent()
    {
        content.Unload();
        foreach (var effect in effectList)
        {
            DeactivateEffect(effect.Key);
        }
    }

    public void Update(GameTime gameTime)
    {
        foreach (var effect in effectList)
        {
            if(effect.Value.IsActive)
                effect.Value.Update(gameTime);
        }
    }

    public void Draw(SpriteBatch spriteBatch)
    {
        origin = new Vector2(SourceRect.Width / 2, SourceRect.Height / 2);
        spriteBatch.Draw(Texture, Position + origin, SourceRect, Color.White * Alpha, 0.0f, origin, Scale, SpriteEffects.None, 0.0f);
    }
}

EDIT:

I've finally managed to get it working properly!

Fixed code:

public class Image
{
    public float Alpha;
    public string Text, FontName, Path;
    public Vector2 Position, Scale;
    public Rectangle SourceRect;
    public bool IsActive;
    public bool Logo;
    public Texture2D Texture;
    Vector2 origin;
    Vector2 dimensions;
    ContentManager content;
    RenderTarget2D renderTarget;
    SpriteFont font;
    Dictionary<string, ImageEffect> effectList;
    public string Effects;

    public FadeEffect FadeEffect;

    void SetEffect<T>(ref T effect)
    {
        if (effect == null)
            effect = (T)Activator.CreateInstance(typeof(T));
        else
        {
            (effect as ImageEffect).IsActive = true;
            var obj = this;
            (effect as ImageEffect).LoadContent(ref obj);
        }

        effectList.Add(effect.GetType().ToString().Replace("RPG.", ""), (effect as ImageEffect));
    }

    public void ActivateEffect(string effect)
    {
        if (effectList.ContainsKey(effect))
        {
            effectList[effect].IsActive = true;
            var obj = this;
            effectList[effect].LoadContent(ref obj);
        }
    }

    public void DeactivateEffect(string effect)
    {
        if (effectList.ContainsKey(effect))
        {
            effectList[effect].IsActive = false;
            effectList[effect].UnloadContent();
        }
    }

    public void StoreEffects()
    {
        Effects = String.Empty;
        foreach (var effect in effectList)
        {
            if (effect.Value.IsActive)
                Effects += effect.Key + ":";
        }

        if(Effects != String.Empty)
            Effects.Remove(Effects.Length - 1);
    }

    public void RestoreEffects()
    {
        foreach (var effect in effectList)
            DeactivateEffect(effect.Key);
        string[] split = Effects.Split(':');
        foreach (string s in split)
            ActivateEffect(s);
    }

    public Image()
    {
        Path = Text = Effects = String.Empty;
        FontName = "Fonts/FixedSys Ex";
        Position = Vector2.Zero;
        Scale = Vector2.One;
        Alpha = 1.0f;
        SourceRect = Rectangle.Empty;
        effectList = new Dictionary<string, ImageEffect>();
    }

    public void LoadContent()
    {
        content = new ContentManager(ScreenManager.Instance.Content.ServiceProvider, "Content");


        if (Path != String.Empty)
            Texture = content.Load<Texture2D>(Path);

        font = content.Load<SpriteFont>(FontName);

        dimensions = Vector2.Zero;

        if (Texture != null)
            dimensions.X += Texture.Width;
        dimensions.X += font.MeasureString(Text).X;

        if (Texture != null)
            dimensions.Y = Math.Max(Texture.Height, font.MeasureString(Text).Y);
        else
            dimensions.Y = font.MeasureString(Text).Y;

        if (SourceRect == Rectangle.Empty)
            SourceRect = new Rectangle(0, 0, (int)dimensions.X, (int)dimensions.Y);

        SetEffect<FadeEffect>(ref FadeEffect);

        LoadDevice();

        if (Effects != string.Empty)
        {
            string[] split = Effects.Split(':');
            foreach (string item in split)
                ActivateEffect(item);
        }

    }

    public void LoadDevice()
    {
        if (Path != String.Empty)
            Texture = content.Load<Texture2D>(Path);

        font = content.Load<SpriteFont>(FontName);

        renderTarget = new RenderTarget2D(ScreenManager.Instance.GraphicsDevice, (int)dimensions.X, (int)dimensions.Y);
        ScreenManager.Instance.GraphicsDevice.SetRenderTarget(renderTarget);
        ScreenManager.Instance.GraphicsDevice.Clear(Color.Transparent);
        ScreenManager.Instance.SpriteBatch.Begin();
        if (Texture != null)
            ScreenManager.Instance.SpriteBatch.Draw(Texture, Vector2.Zero, Color.White);
        ScreenManager.Instance.SpriteBatch.DrawString(font, Text, Vector2.Zero, Color.White);
        ScreenManager.Instance.SpriteBatch.End();

        Texture = renderTarget;

        ScreenManager.Instance.GraphicsDevice.SetRenderTarget(null);
    }

    public void UnloadContent()
    {
        content.Unload();
        foreach (var effect in effectList)
        {
            DeactivateEffect(effect.Key);
        }
    }

    public void Update(GameTime gameTime)
    {
        foreach (var effect in effectList)
        {
            if(effect.Value.IsActive)
                effect.Value.Update(gameTime);
        }
    }

    public void Draw(SpriteBatch spriteBatch)
    {
        origin = new Vector2(SourceRect.Width / 2, SourceRect.Height / 2);
        spriteBatch.Draw(Texture, Position + origin, SourceRect, Color.White * Alpha, 0.0f, origin, Scale, SpriteEffects.None, 0.0f);

        if (renderTarget.IsContentLost)
        {
            ScreenManager.Instance.SpriteBatch.End();
            LoadDevice();
            ScreenManager.Instance.SpriteBatch.Begin();
        }
    }
}

The contents of renderTarget are now drawn in a seperate method, and is being called in LoadContent() once, and in the Draw() method whenever the contents are lost.

Answer 1

So the problem here arises from the fact that you're using a RenderTarget2D as your texture.

In pure DirectX, both textures and render targets lose their contents whenever the graphics device is lost. This is because everything in video memory--where your textures live--has to be unloaded. XNA abstracts this away from you with respect to textures: it keeps a copy of the texture in CPU memory so that it can automatically recreate it after the device is reset.

Render targets are a trickier thing, however. You're not usually loading a render target from a pre-existing image; rather, you're generating the render target contents directly on the GPU itself. So how does XNA recreate your render targets for you, if it can't hold a copy of their contents in CPU memory? The answer is that it can't. When the device is lost, your render targets lose their contents and there's nothing that XNA can do about it.

This is why the RenderTarget2D class exposes a property called IsContentLost. This allows you to determine when the above scenario has happened and respond appropriately. You don't need to create a new render target--the object still exists in memory--but you need to tell the graphics device what it contains again.

Right now, you're drawing your render target in LoadContent(), which is only ever called once. You need to move the part of that code responsible for drawing the render target into another method, and call that method whenever the render target is lost.

Now, to draw the render target, you need to set it on the graphics device using SetRenderTarget(myRenderTarget). Once you're done drawing it, you need to unset it again using SetRenderTarget(null), which restores the backbuffer as the primary render target. This is important because a render target can't be both a source of rendering (i.e. a texture) and a target of rendering at the same time. If you try to do that, you'll get an exception.

Your situation seems to be complicated by the fact that you're loading a texture into the Texture field, then drawing it to a render target, then replacing the Texture field with the render target. If you try to do what I just described with what you have, you're going to end up trying to draw the render target onto itself--that's probably what's causing the exception that you're seeing. So don't do that. Store the original texture in a different field, because you'll need it later to regenerate the target.

Answer 2

I ran into the same problem and found a (more elegant?) way to fix this. Which doesn't involve redrawing the initial textures (since switching render targets is costly).

public void Initialize(GraphicsDevice graphics)
{
    Color[] colors = new Color[Width * Height];
    RenderTarget2D target = new RenderTarget2D(graphics, Width, Height);
    gridTexture = new Texture2D(graphics, Width, Height);

    graphics.SetRenderTarget(target);
    graphics.Clear(Color.Black);

    SpriteBatch.Begin();
    // drawing code...
    SpriteBatch.End();

    graphics.SetRenderTarget(null);

    target.GetData<Color>(colors);
    gridTexture.SetData<Color>(colors);
}

I realize it's a bit late but hopefully it will help someone who comes along...