是否需要鎖定才能修復？

Question

我有有錯誤一些代碼「AccessViolationException是由用戶代碼未處理：嘗試讀取或寫入受保護的內存...」

一個下調違規版本功能如下：

protected override void OnPaint(PaintEventArgs pe) 
{ 
    if ((updatingFastBackground) || (Calculating)) return; //ADDED FOR DEBUGGING, SEE BELOW 
      BitmapData canvasData = Canvas.LockBits(new Rectangle(Point.Empty, Canvas.Size), ImageLockMode.WriteOnly, FastPixelFormat); 
      BitmapData fbgData = fastBackground.LockBits(new Rectangle(Point.Empty, fastBackground.Size), ImageLockMode.ReadOnly, FastPixelFormat); 
      try 
      { 
       unsafe 
       { 
        byte* canvasDataScan0 = (byte*)canvasData.Scan0.ToPointer(); 
        byte* fbgDataScan0 = (byte*)fbgData.Scan0.ToPointer(); 
        Rectangle spriteBounds = new Rectangle(Point.Empty, ButtonImages.ImageSize); 
        for (int i = 0; i < ButtonImages.Images.Count; i++) 
        { 
         // Button offset location 
         Point l = new Point(
          (int)((i % columnCount) * hStep + myIVM.Location.X), 
          (int)((i/columnCount) * vStep + myIVM.Location.Y)); 
         // Paint at current location? 
         if (buttonPaintBounds.Contains(l)) 
         { 
          BitmapData spriteData = buttonBitmaps[i].LockBits(spriteBounds, ImageLockMode.ReadOnly, FastPixelFormat); 
          try 
          { 
           int spriteLeft = Math.Max(l.X, 0); 
           int spriteRight = Math.Min(l.X + ButtonImages.ImageSize.Width, canvasData.Width); 
           int spriteTop = Math.Max(l.Y, 0); 
           int spriteBottom = Math.Min(l.Y + ButtonImages.ImageSize.Height, canvasData.Height); 
           int spriteWidth = spriteRight - spriteLeft; 
           int spriteHeight = spriteBottom - spriteTop; 
           byte* canvasRowLeft = canvasDataScan0 + (spriteTop * canvasData.Stride) + spriteLeft * 4; 
           byte* spriteRowLeft = 
            (byte*)spriteData.Scan0.ToPointer() + 
            Math.Max((spriteTop - l.Y), 0) * spriteData.Stride + 
            Math.Max((spriteLeft - l.X), 0) * 4; 
           for (int y = 0; y < spriteHeight; y++) 
           { 
            canvasRowLeft += canvasData.Stride; 
            spriteRowLeft += spriteData.Stride; 
            Byte* canvasWalk = (Byte*)canvasRowLeft; 
            Byte* spriteWalk = (Byte*)spriteRowLeft; 
            for (int x = 0; x < spriteWidth; x++) 
            { 
             if (spriteWalk[3] != 255) 
             { 
              canvasWalk[0] = (byte)(canvasWalk[0] * spriteWalk[3]/255 + spriteWalk[0]); 
              canvasWalk[1] = (byte)(canvasWalk[1] * spriteWalk[3]/255 + spriteWalk[1]); 
              canvasWalk[2] = (byte)(canvasWalk[2] * spriteWalk[3]/255 + spriteWalk[2]); 
             } 
             canvasWalk += 4; 
             spriteWalk += 4; 
            } 
           } 
           thesePoints.Add(l); 
          } 
          finally 
          { 
           buttonBitmaps[i].UnlockBits(spriteData); 
          } 
         } 

canvasWalk[0] = 0; 

：當與替換

canvasWalk[0] = (byte)(canvasWalk[0] * spriteWalk[3]/255 + spriteWalk[0]); 

甚至：在線路中發生

錯誤

迭代變量y和x每次崩潰時都有不同的值，所以這讓我相信一個外部函數正在修改位圖。

如果這實際上是我的問題，是否有辦法阻止fastBackground和Canvas被外部修改？我以爲LockBits是應該做的是...

如果這還不夠回答，這裏的多一些我已經試過： 我增加了行

if ((updatingFastBackground) || (Calculating)) return; 

如果fastBackgroundCanvas或退出的OnPaint其他功能正在修改尺寸。

我能使用互斥來防止修改從在同一時間油漆中運行（因爲我認爲他們必須）的位圖fastBackground和Canvas的功能，但我寧願阻止他們的另一種方式爲畫布是公開的，我不想要求在課堂上傳遞互斥鎖。

每@usr的建議，這個進一步修剪版本不會失敗......必須是PTD錯誤。 （程序員太愚蠢），即算術錯誤

protected override void OnPaint(PaintEventArgs pe) 
{ 
    if ((updatingFastBackground) || (Calculating)) return; //ADDED FOR DEBUGGING, SEE BELOW 
      BitmapData canvasData = Canvas.LockBits(new Rectangle(Point.Empty, Canvas.Size), ImageLockMode.WriteOnly, FastPixelFormat); 
      BitmapData fbgData = fastBackground.LockBits(new Rectangle(Point.Empty, fastBackground.Size), ImageLockMode.ReadOnly, FastPixelFormat); 
      try 
      { 
       unsafe 
       { 
        byte* canvasDataScan0 = (byte*)canvasData.Scan0.ToPointer(); 
        byte* fbgDataScan0 = (byte*)fbgData.Scan0.ToPointer(); 
        Rectangle spriteBounds = new Rectangle(Point.Empty, ButtonImages.ImageSize); 
        for (int i = 0; i < ButtonImages.Images.Count; i++) 
        { 
         // Button offset location 
         Point l = new Point(
          (int)((i % columnCount) * hStep + myIVM.Location.X), 
          (int)((i/columnCount) * vStep + myIVM.Location.Y)); 
         // Paint at current location? 
         if (buttonPaintBounds.Contains(l)) 
         { 
          BitmapData spriteData = buttonBitmaps[i].LockBits(spriteBounds, ImageLockMode.ReadOnly, FastPixelFormat); 
          try 
          { 
           byte* canvasRowLeft = canvasDataScan0; 
           byte* spriteRowLeft = (byte*)spriteData.Scan0.ToPointer(); 
           for (int y = 0; y < 145; y++) 
           { 
            canvasRowLeft += canvasData.Stride; 
            spriteRowLeft += spriteData.Stride; 
            Byte* canvasWalk = (Byte*)canvasRowLeft; 
            Byte* spriteWalk = (Byte*)spriteRowLeft; 
            for (int x = 0; x < 145; x++) 
            { 
             if (spriteWalk[3] != 255) 
             { 
              canvasWalk[0] = 0; 
              canvasWalk[1] = 0; 
              canvasWalk[2] = 0; 
             } 
             canvasWalk += 4; 
             spriteWalk += 4; 
            } 
           } 
           thesePoints.Add(l); 
          } 
          finally 
          { 
           buttonBitmaps[i].UnlockBits(spriteData); 
          } 
         } 

Answer 1

移動我的評論到答案，因爲它幫助解決的問題：

固定不需要通過LockBits返回的緩衝區，因爲它是託管內存。你的指針算術是錯誤的。找到錯誤。創建一個簡單的repro來幫助查找錯誤。