我有一些代码出现错误“AccessViolationException 未被用户代码处理：尝试读取或写入受保护的内存......”
违规函数的精简版本如下：
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);
}
}
错误发生在该行：
canvasWalk[0] = (byte)(canvasWalk[0] * spriteWalk[3] / 255 + spriteWalk[0]);
甚至替换为：
canvasWalk[0] = 0;
迭代变量在每次崩溃时都有不同的值，所以这让我相信外部函数正在修改y位图。xCanvas
如果这实际上是我的问题，有没有办法防止fastBackground和Canvas被外部修改？我以为LockBits应该这样做...
如果这还不足以回答，这里有一些我已经尝试过：我添加了这一行
if ((updatingFastBackground) || (Calculating)) return;
fastBackground Canvas如果或尺寸正在被其他函数修改，则退出 OnPaint 。
我可以使用互斥锁来防止修改位图的函数fastBackground与Canvas绘图同时运行（我认为它们必须如此）但我宁愿以另一种方式阻止它们，因为 Canvas 是公共的，我不想要要求将互斥锁从类中传递出去。
根据@usr 的建议，这个进一步精简的版本不会失败……一定是 PTD 错误。（程序员太笨了）即算术错误
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);
}
}