我应该如何以及在哪里放置旧图像？ 以及将pictureBox中的图像设置为最小和最大的大小是多少？

Question

Im using the mouse wheel to zoom in/out an image in a pictureBox:

In the top of form1:

double increment = 1.25;
double factor = 1.0;
Image img;

In the constructor:

img = new Bitmap(@"d:\radar000075.png");
pictureBox1.Load(@"d:\radar000075.png");

Then two events and resize mthod:

void pictureBox1_MouseHover(object sender, EventArgs e)
        {
            pictureBox1.Focus();
        }

        void pictureBox1_MouseWheel(object sender, MouseEventArgs e)
        {
            if (e.Delta > 0)
                factor *= increment;
            else
                factor /= increment;
            pictureBox1.Image = resizeImage(img, new Size((int)(img.Width * factor), (int)(img.Height * factor)));
        }

        public static Image resizeImage(Image imgToResize, Size size)
        {
            return (Image)(new Bitmap(imgToResize, size));
        }

Now its working without any problems but:

1. In the mouse wheel event i assign to the pictureBox.Iamge each time the original image and using the resizeImage method. Do i need to dispose somewhere each time the original image (img) ? Or the old image i assigned somehow ?

2. How and where do i set the limits for the image resize now its resizing the image by 25% small or big but there should be a limit how big i can zoom in and how small i can zoom out where and how do i set this limits ?

Answer 1

Bitmap implements the IDisposable interface so, yes, technically you should dispose of it once you're finished using it. Otherwise it will be up to the Garbage Collector to do it, and you never know when it will trigger. So you may see your memory consumption go up and down if you resize a lot of times because of the new bitmap you're creating each time.

For the factor limitation, personally I'd extract the current factor calculation code from pictureBox1_MouseWheel and add it in the new method. It's not really the event business to know about resizing so it should be in a separate method (You should take a look at the Single Responsibility Principle ). Simply adding an other condition to your already existing if could easily do the job. It could be something along those lines :

void pictureBox1_MouseWheel(object sender, MouseEventArgs e)
{
    CalculateNewSizeFactor(e.Delta);
    pictureBox1.Image = resizeImage(img, new Size((int)(img.Width * factor), (int)(img.Height * factor)));
}

private void CalculateNewSizeFactor(int delta)
{
    if (delta > 0 && factor < 2)
    {
        factor *= increment;
    }
    else if (delta < 0 && factor > 0.25)
    {
        factor /= increment;
    }
}

Basically you resize only if the factor is smaller than, let's say, 2 and greater than 0.25.

Also, here's some quick recommendations for your code :

• Methods in C# are usually typed in CamelCase, so resizeImage should be ResizeImage .
• img is already declared at class level, you do not need to pass it to resizeImage as a parameter
• avoid using the static modifier if you don't intend to use the method statically.
• You do not need to cast the bitmap as an Image

so your method can be simplified to

public Image ResizeImage(Size size)
{
    return new Bitmap(img, size);
}