c#-对于循环,应用程序挂起

好吧,我正在创建一个应用程序,我在使用for循环来基本上读取图像的每个像素,寻找像素颜色(简单的东西)中的图案.无论如何,由于某种原因,我的应用程序只是锁定而从未恢复到正常状态.我一次又一次地遍历代码,而没有看到任何实际的问题.

我唯一注意到的是ScanPixelsLater中的for循环可能提前退出.我已经尽可能地注释了代码,

private Point topLeftc, bottomLeftc, topRightc, bottomRightc;

/// <summary>
/// Starts the initial looping process, designed only to loop through ONCE, ScanPixelsLater takes over
/// </summary>
/// <param name="img">Image to scan</param>
public void ScanPixels(Bitmap img)
{
    int whitePixel = 0;

    for (int y = 100; y < img.Height; y++)
    {

        for (int x = 100; x < img.Width; x++)
        {

            if (img.GetPixel(x, y) == Color.FromArgb(255, 255, 255, 255))
            {
                // img.SetPixel(x, y, Color.Green);
                whitePixel++;

            }
            else { whitePixel = 0; }


            if (whitePixel == 18)
            {
                whitePixel = 0;
                topLeftc = new Point(x - 18, y);
                DetectNextWhiteLine(topLeftc, img);

            }
        }
    }


}


/// <summary>
/// First creates the TopRight value via using the last pixel in x range, and using the current Y value
/// Then a Y loop is started 10 pixels down, within this loop is another X loop which scans the X range
/// If 10 consecutive white pixels are found, the TopLeft X value and the current Y value are used to map the 
/// BottomLeft and BottomRight coordinates. Finally a new Point is created which starts (x = 1) and (y = currentYValue + 2)
/// The ScanPixelsLater method is then called, passing the new Point (newLocation).
/// 
/// </summary>
/// <param name="p">The x and y value of where the pixels were found</param>
/// <param name="img">Image being used</param>
private void DetectNextWhiteLine(Point p, Bitmap img)
{

    int whitePixel = 0;
    topRightc = new Point(img.Width, topLeftc.Y);

    for (int y = p.Y + 10; y < img.Height; y++)
    {

        for (int x = p.X - 5; x < img.Width; x++)
        {
            if (img.GetPixel(x, y) == Color.FromArgb(255, 255, 255, 255))
            {
                whitePixel++;
            }
            else
            {
                whitePixel = 0;
            }

            if (whitePixel == 10)
            {
                bottomLeftc = new Point(topLeftc.X, y);
                bottomRightc = new Point(img.Width, y);
                Cords.Add(new Coordinates(topLeftc, topRightc, bottomLeftc, bottomRightc));

                Point newLocation = new Point(1, y + 2);
                calls++;
                ScanPixelsLater(newLocation, img); //rescan the image from new y axis 
            }
        }
    }

}



/// <summary>
/// Loops through the pixels based on the p parameter, if 15 white pixels are found, the location (x & y) is
/// passed to the DetectNextWhiteLine method which fixes the next line with a similar number of white pixels.
/// </summary>
/// <param name="p">The Point(x,y) at which to start scanning</param>
/// <param name="img"></param>
private void ScanPixelsLater(Point p, Bitmap img)
{

    int whitePixel = 0;

    for (int y = p.Y; y < img.Height; y++)
    {

        for (int x = p.X; x < img.Width; x++)
        {
            if (img.GetPixel(x, y) == Color.FromArgb(255, 255, 255, 255))
            {
                whitePixel++;
            }
            else
            {
                whitePixel = 0;
            }

            if (whitePixel == 15)
            {
                bottomLeftc = new Point(topLeftc.X, y);
                topLeftc = new Point(x - 15, y);
                calls++;
                DetectNextWhiteLine(topLeftc, img);
            }

        }
    }

    // only want this to execute after all the pixels within the entire img have been read
    // possibly executing early.

    DrawWhiteLines(img);
    AppArgs aa = new AppArgs(true);
    Change(this, aa); // custom event handler, fired behind form to update GUI

}

解决方法:

因此,要了解您的应用程序为何挂起,您需要了解WinForm应用程序的工作原理.

您的UI所运行的线程也具有所谓的消息泵.此消息泵包含从操作系统(和其他来源)传递到所有UI元素的消息.他们告诉他们何时更改状态,何时重绘自身等.当您的循环很长时,消息泵将无法处理消息.获取排队,但从未处理,这就是应用程序“挂起”的含义.

您的应用程序永远都不可能恢复.您的循环最终将结束,您的UI将再次变得响应(假设我没有在某个地方错过无限循环,但我不认为我做到了).但是,GDI GetPixel方法确实非常慢,并且如果您的图像很大,那么这组循环将需要很长时间才能完成.您可能必须深入研究不安全的上下文,并使用LockBits获取指向图像内存的指针.这里有很多如何做到这一点的例子.

编辑：在更仔细地查看您的代码后,也很明显它效率相对较低.那里至少有6个嵌套的for循环嵌套层,因此当您只需要单次扫描时,实际上就需要多次扫描图像.

图像处理是一个资源密集的过程.您需要小心,以尽可能高效地完成所有性能密集型工作.

标签：loops,for-loop,c,nested-loops
来源： https://codeday.me/bug/20191105/1995526.html