IconOverlayHandler Doesn't overlay icon of the file

Question

namespace SyncFileIconOverlay
{
[ComVisible(true)]
public class SyncFileIconOverlay:SharpIconOverlayHandler
{
   
    protected override int GetPriority()
    {
        //  The read only icon overlay is very low priority
        return 90;
    }

    public int PriorityGetter()
    {
        return GetPriority();
    }

    protected override bool CanShowOverlay(string path, FILE_ATTRIBUTE attributes)
    {
        try
        {
            //  Get the file attributes
            var fileAttributes = new FileInfo(path);

            //  Return true if the file is read only, meaning we'll show the overlay
            return true;
        }
        catch (Exception)
        {
            return false;
        }
    }

    public bool CanShowOverlayGetter(string path)
    {
        return CanShowOverlay(path, FILE_ATTRIBUTE.FILE_ATTRIBUTE_NORMAL);
    }

    protected override System.Drawing.Icon GetOverlayIcon()
    {
        //  Return the read only icon
        return Properties.Resources.ReadOnly;
    }

    public System.Drawing.Icon OverlayIconGetter()
    {
        return GetOverlayIcon();
    }

   }
}

I am using the code above which I find from https://www.codeproject.com/Articles/545781/NET-Shell-Extensions-Shell-Icon-Overlay-Handlers

this is in a Class library and I reference this dll from my winform application when I need to overlayicon I am calling PriorityGetter then check with CanShowOverlayGetter finally call the OverlayIconGetter, If the CanShowOverlay function is returning true for a file it changes overlay icon but the problem is system uses this for every file in my computer without me doing anything when i register the dll and restart the explorer changes applies, but i want to check and change the icon overlay from a winform project that uploads and downloads files i want make icon overlay on those files that comes dynamically from the program. Do you guys have any idea how can i achieve this thanks!!!

Answer 1

You need to the some work before your icon overlay works because of the limit. You can check it here Making Icon Overlays Appear In Windows 7 and Windows 10.

...have a hard limit of 15 overlays. There’s a list in the registry, and no matter how many apps install overlays, only the first 15 are used. The rest are ignored.

Update 1
I couldn't find a better way to do it via file. But this sample will show overlay icon on specific folder.

Step 1: Set a file marker that can be hidden. In my sample i have .marker it's just a blank file.

Step 2: Your overlay icon handler.

[ComVisible(true)]
public class FileValidIconOverlayHandler : SharpIconOverlayHandler
{
    protected override int GetPriority()
    {
        return 10;
    }

    protected override bool CanShowOverlay(string path, FILE_ATTRIBUTE attributes)
    {
        var file = new FileInfo(path);
        var hasFileMarker = file.Directory.GetFiles(".marker").Length > 0;
        var isNotFileMarker = file.Name != ".marker";
        var isNotDirectory = !file.Attributes.HasFlag(FileAttributes.Directory);

        return hasFileMarker && isNotFileMarker && isNotDirectory;
    }

    protected override System.Drawing.Icon GetOverlayIcon()
    {
        return Properties.Resources.Valid;
    }
}

Output with .marker

Output without .marker