C# - on mouseover at taskbar, a preview is generat

Question

I am developing a winForm application in which i am list all the running processes. on mouseover of any process, i want preview window like (In Windows 7, when you mouse over an application in your task bar, a preview is generated showing the contents of the application window.) See Image.

Any idea how to achieve this, i am not able to get it. Any suggestion will be helpful. Thanks..

Answer 1

full example at this site
You need two functions :

[DllImport("dwmapi.dll")]
static extern int DwmRegisterThumbnail(IntPtr dest, IntPtr src, out IntPtr thumb);

[DllImport("dwmapi.dll")]
static extern int DwmUpdateThumbnailProperties(IntPtr hThumb, ref DWM_THUMBNAIL_PROPERTIES props);

usage of DwmRegisterThumbnail
you are at your form, and process it a external program that you want to paint at your program.

IntPtr hWnd = process.MainWindowHandle;
int i = DwmRegisterThumbnail(this.Handle, hWnd, out thumb);

after registration, you just saying to windows the location to paint the picture

            DWM_THUMBNAIL_PROPERTIES props = new DWM_THUMBNAIL_PROPERTIES();

            props.fVisible = true;
            props.dwFlags = DWM_TNP_VISIBLE | DWM_TNP_RECTDESTINATION | DWM_TNP_OPACITY;
            props.opacity = 255;
            props.rcDestination = new Rect(panel.Left, panel.Top, panel.Right, panel.Bottom);

            DwmUpdateThumbnailProperties(thumb, ref props);

Answer 2

You don't need to write any code to make this happen. It's part of the Aero theme, introduced with Windows Vista and still present in Windows 7. By default, a little thumbnail of the application's window is shown when you hover over its icon in the taskbar. That's true for the Skype example you showed, and also for a C# application that you write yourself.

If you want a finer level of control over exactly what gets shown in the preview (like if you only wanted to show a small portion of your app's window), you can write some code that calls one or more of the relevant DWM API functions.

But don't write all of the P/Invoke code yourself. Use one of the existing libraries that wraps it all up in a .NET friendly way, like Windows Forms Aero or the Windows API Code Pack.

Answer 3

If you want your own application to display an Aero thumbnail, maybe this C++ sample could help you. Apparently it uses DwmRegisterThumbnail() to say "This HWND will now display a thumbnail of this other one".

So, a little P/Invoke call and IWin32Window...