当游戏最小化时，RenderTarget内容会更改

Question

So I'm working on a GUI library for XNA and I've come across an issue I can't find a solution to. I'm working with rendertargets a lot, which is annoying in itself, but I have a really weird and specific issue.

In my ProgressBar class I'm drawing the individual components when the element is Validated and the object size has changed. If the object is Validated but the object size did not change, I use the filled rendertargets as textures to draw the final product onto a buffer-texture (again a rendertarget). Now, whenever I minimize the application, and tab in again, the background layer of the progressbar will have an imprint of the striped texture above it on it. The rendertargets are set to preserve content and I made sure that the correct rendertargets are set. ALSO clearing the graphicsDevice (just below the "Actual Drawing" line) does not do anything. Why?

So basically the game creates a screenshot of the area, and draws it into my texture. What the hell?

Here is the code for the ProgressBar:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
namespace PixLib
{
    public class ProgressBar : UIElement
    {
        private float stripeThickness = 5;
        private float stripeGapFactor = 3f;
        private float animationSpeed = 1f;
        private float at = 0;
        private RenderTarget2D stripesBg, stripes;
        private Coordinate2 lastSize;
        protected override Coordinate2 InnerArea
        {
            get { return Coordinate2.Zero; }
        }
        protected Color color;
        public Color Color
        {
            get
            {
                return color;
            }
            set
            {
                color = value;
                Invalidate();
            }
        }
        protected float value;
        public float Value
        {
            get
            {
                return value;
            }
            set
            {
                float t = Math.Min(1, Math.Max(0, value));
                if (t != this.value)
                {
                    this.value = t;
                    Invalidate();
                }

            }
        }
        public ProgressBar(string name,Color color, Rectangle elementRect, bool localPos = true)
            : base(name, elementRect, localPos)
        {
            lastSize = new Coordinate2();
            this.color = color;
            value = 0;
            at = 0;
        }
        protected override void OnUpdate(MouseState mouseState, KeyboardState keyboardState)
        {

        }
        protected override void OnInit()
        {

        }
        protected override void Redraw(SpriteBatch spriteBatch)
        {

            if (lastSize.X != Width || lastSize.Y != Height)
            {

                Console.WriteLine("Redrawing Progressbar");
                //redraw textures!
                stripesBg = new RenderTarget2D(graphicsManager.GraphicsDevice, Width, Height, false, graphicsManager.GraphicsDevice.DisplayMode.Format, DepthFormat.Depth24, 1, RenderTargetUsage.PreserveContents);
                stripes = new RenderTarget2D(graphicsManager.GraphicsDevice, Width, Height * 2, false, graphicsManager.GraphicsDevice.DisplayMode.Format, DepthFormat.Depth24, 1, RenderTargetUsage.PreserveContents);

                spriteBatch.Begin();
                spriteBatch.Draw(pixel, new Rectangle(0, 0, Width, Height), Color.White);
                spriteBatch.End();

                SetRenderTarget(stripesBg);
                spriteBatch.Begin();
                spriteBatch.Draw(pixel, new Rectangle(0, 0, Width, Height), Color.White);
                spriteBatch.End();

                /*SetRenderTarget(border);
                spriteBatch.Begin();
                int si = (int)(stripeThickness*0.5f + 0.5f);
                DrawLine(new Coordinate2(si, 0), new Coordinate2(Width, 0), spriteBatch, Color.White, si);
                DrawLine(new Coordinate2(si, Height - si), new Coordinate2(Width, Height - si), spriteBatch, Color.White, si);
                DrawLine(new Coordinate2(si, 0), new Coordinate2(si, Height), spriteBatch, Color.White, si);
                DrawLine(new Coordinate2(Width, 0), new Coordinate2(Width, Height - si), spriteBatch, Color.White, si);
                spriteBatch.End();*/

                SetRenderTarget(stripes);
                spriteBatch.Begin();
                int fy = (int)(stripeThickness +0.5f);
                int s = (Height + fy) * 2;
                int fx = -s;
                at = 0;
                while (fx < Width + stripeThickness * stripeGapFactor)
                {

                    DrawLine(new Coordinate2(fx, -fy), new Coordinate2(fx+s, s-fy), spriteBatch, Color.White, stripeThickness);
                    fx += (int)(stripeThickness * stripeGapFactor);
                }
                spriteBatch.End();


                SetRenderTarget(null);


                lastSize.X = Width;
                lastSize.Y = Height;
            }

            //actual drawing
            spriteBatch.Begin();
            spriteBatch.Draw(pixel, SizeRect, Darken(color, 2));
            int cv = (int)(Value * Width + 0.5f);
            spriteBatch.Draw(stripesBg, new Rectangle(cv - Width, 0, Width, Height), Darken(Color));
            graphicsManager.GraphicsDevice.Clear(Color.Transparent);
            spriteBatch.Draw(stripes, new Rectangle(cv - Width, -(int)(at + 0.5f), Width, Height * 2), color);
            spriteBatch.End();

            at += animationSpeed;
            if (at >= Height)
                at -= Height - (int)(stripeThickness + .5f);
        }
    }
}

Answer 1

Okay, it seems that the solution to this problem was to make the rendertargets not keep their content, and to redraw the whole damn thing whenever the content is lost.

 if (lastSize.X != Width || lastSize.Y != Height || stripesBg.IsContentLost || stripes.IsContentLost)
            {

                Console.WriteLine("Redrawing Progressbar");
                //redraw textures!
                //stripesBg = new RenderTarget2D(graphicsManager.GraphicsDevice, Width, Height, false, graphicsManager.GraphicsDevice.DisplayMode.Format, DepthFormat.Depth24, 1, RenderTargetUsage.PreserveContents);
                //stripes = new RenderTarget2D(graphicsManager.GraphicsDevice, Width, Height * 2, false, graphicsManager.GraphicsDevice.DisplayMode.Format, DepthFormat.Depth24, 1, RenderTargetUsage.PreserveContents);
                stripesBg = new RenderTarget2D(graphicsManager.GraphicsDevice, Width, Height);
                stripes = new RenderTarget2D(graphicsManager.GraphicsDevice, Width, Height * 2);
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