在Winforms中显示动画gif而不锁定文件

Question

I'm trying to display images of various file types (including animated .gif files) in my Winforms application. I also have to be able to modify the files that are shown . (change the file name, delete them).

The problem is that a Picturebox locks the image file until the application is closed when using the normal way.

That means I can't do this:

private void Form1_Load(object sender, EventArgs e)
    {

        PictureBox pic = new PictureBox();
        pic.Size = new Size(250, 250);
        pic.Image = Image.FromFile("someImage.gif");
        this.Controls.Add(pic);

                    //No use to call pic.Image = null or .Dispose of it
        File.Delete("someImage.gif"); //throws exception
    }

The workaround in the link above is as follows:

    private void Form1_Load2(object sender, EventArgs e)
    {
        PictureBox pic = new PictureBox();
        pic.Size = new Size(250, 250);
                    //using a FileStream
        var fs = new System.IO.FileStream("someImage.gif", System.IO.FileMode.Open, System.IO.FileAccess.Read);
        pic.Image = System.Drawing.Image.FromStream(fs);
        fs.Close();

        this.Controls.Add(pic);

        pic.MouseClick += pic_MouseClick;
    }

That works fine for normal image types, but it won't load animated .gifs, which is important to me. Trying to load one will make it look like this .

I've found a few other topics about it ( this and this ) but they're all about WPF and use BitmapImage. I've searched about how to use BitmapImage in a Winforms application, but haven't found anything apart from that it is supposed to somehow work.

I would like to stay with Winforms because I'm just getting used to it, but that's not a necessity.

To summarize: I need a way to show common image types (png, jpg, bmp, and animated gif) while still being able modify the file on the HDD. It is OK if that means unloading->modifying->reloading the file. I'd prefer Winforms, but other Frameworks would do.

Thanks for your help.

Edit: Another way I've tried

using (System.IO.FileStream fs = new System.IO.FileStream("E:\\Pics\\small.gif", System.IO.FileMode.Open, System.IO.FileAccess.Read))
        {
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            fs.CopyTo(ms);
            pic.Image = Image.FromStream(ms);
        } 

But shows the same problem as the second example. The gif doesn't load.

Answer 1

Using a MemoryStream is indeed the right way to avoid the file lock. Which is a strong optimization btw, the lock is created by the memory-mapped file that the Image class uses to keep the pixel data out of the paging file. That matters a great deal when the bitmap is large. Hopefully not on an animated gif :)

A small mistake in your code snippet, you forgot to reset the stream back to the start of the data. Fix:

 using (var fs = new System.IO.FileStream(...)) {
     var ms = new System.IO.MemoryStream();
     fs.CopyTo(ms);
     ms.Position = 0;                               // <=== here
     if (pic.Image != null) pic.Image.Dispose(); 
     pic.Image = Image.FromStream(ms);
 } 

In case it needs to be said: do not dispose the memory stream. That causes very hard to diagnose random crashes later, pixel data is read lazily.

Answer 2

Essentialy you'll have to make a copy of the image file in your memory .

Pre .Net 4.0 (2.0,3.0,3.5) you'd have to create a FileStream and copy it to a MemoryStream and rewind it, as seen in another answer.

Since .Net 4.0 (4.0,4.5,...) Image.FromFile supports animated GIF's

---

If you work with .Net 4.0 or later following method will suffice:

Using System.IO , System.Drawing and System.Drawing.Imaging

 private void Form1_Load(object sender, EventArgs e)
    {
        string szTarget = "C:\\someImage.gif";

        PictureBox pic = new PictureBox();
        pic.Dock = DockStyle.Fill;

        Image img = Image.FromFile(szTarget);   // Load image fromFile into Image object

        MemoryStream mstr = new MemoryStream(); // Create a new MemoryStream
        img.Save(mstr, ImageFormat.Gif);        // Save Image to MemoryStream from Image object

        pic.Image = Image.FromStream(mstr); // Load Image from MemoryStream into PictureBox
        this.Controls.Add(pic); 

        img.Dispose(); // Dispose original Image object (fromFile)
        // after this you should be able to delete/manipulate the file

        File.Delete(szTarget);
    }