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You can determine the total size of a Storage Card and available free bytes using the GetDiskFreeSpaceEx API function. Below is a “mini-wrapper” around the function which returns a structure with the three return values. You’ll notice in this example I’m marshalling longs (64bit Integers), values greater than 32bit cannot be marshalled by value but can be marshalled by reference as in this case. The DiskFreeSpace struct contains three long members to hold the accessible free bytes, total bytes and total free bytes.

public static DiskFreeSpace GetDiskFreeSpace(string directoryName)

{

    DiskFreeSpace result = new DiskFreeSpace();

    if(!GetDiskFreeSpaceEx(directoryName, ref result.FreeBytesAvailable,

        ref result.TotalBytes, ref result.TotalFreeBytes))

    {

        throw new Win32Exception(Marshal.GetLastWin32Error(), “Error retrieving free disk space”);

    }

    return result;

}

public struct DiskFreeSpace

{

    public long FreeBytesAvailable;

    public long TotalBytes;

    

    public long TotalFreeBytes;

}

[DllImport(“coredll”)]

private static extern bool GetDiskFreeSpaceEx(string directoryName,

    ref long freeBytesAvailable,

    ref long totalBytes,

    ref long totalFreeBytes);

I’ve posted a new
article to OpenNETCF.org about hosting Native windows controls from within the
.NET Compact Framework. The approach used allows you to host the control within a
Control object and receive notification back from the control thus supporting Events.
The first control to use this technique was the HTMLViewer in the Smart Device Framework
v1.0, but this has already been supplemented with InkX and MonthCalendar controls
in our latest source code. The
bulk of the work required is encapsulated in the ControlMessageWindow so it is a fairly
quick process to implement new controls in this way.

I sincerely hope that we get some extra power in the .NET Compact Framework v2.0 such
as the ability to override the WndProc of the control itself, and built in support
for the Handle property. Of course it is only a week until the Mobility
Developer Conference when more should become clear… I can’t wait!

In the full desktop framework all Controls and Forms expose the Handle property which
represents the native window handle of the control – this can be passed to API functions.
In the Compact Framework this property is not implemented. In the Smart
Device Framework we have created the OpenNETCF.Windows.Forms.IWin32Window interface
which matches the equivalent interface on the full framework. You can implement this
interface in your custom controls and forms to provide a standard way of exposing
the window handle.

Getting the handle to any control requires just one P/Invoked API function – GetCapture
which returns the window handle of the control with capture (able to receive mouse/stylus
input). First Capture is set on the control, then this API call will return the HWND
of the control, finally capture is optionally release from the control. The GetCapture
function is implemented in the OpenNETCF.Win32.Win32Window class,
or you can P/Invoke it directly. The following code illustrates adding IWin32Window
support to your control:-

[VB]

Imports OpenNETCF.Windows.Forms
Imports OpenNETCF.Win32

Public Class MyControl
    Inherits System.Windows.Forms.Control
    Implements IWin32Window
    

    Overridable ReadOnly Property Handle() As System.IntPtr
        Get
            Me.Capture = True

            Dim thishandle As IntPtr
            thishandle = Win32Window.GetCapture()
            Me.Capture = False
            Handle = thishandle
        End Get
    End Property
End Class


[C#]

using OpenNETCF.Windows.Forms;
using OpenNETCF.Win32;

public class MyControl : Control, IWin32Window
{
   public IntPtr Handle
   {
       get
       {
           this.Capture = true;
           IntPtr thishandle = Win32Window.GetCapture();
           this.Capture = false;
           return thishandle;
       }
   }
}

By using the Interface approach rather than adding in support for handles on an ad-hoc
basis you have a garunteed signature for your handle implementation. Therefore
if you have a method which requires a native window handle you can accept an IWin32Window
as an argument. We will be ensuring that all our OpenNETCF controls in the future
implement this interface so you can rely on the Handle property to get the native
window handle.

To co-incide with our latest source-code release of the Smart
Device Framework, we’ve implemented an online
source browser which you can use to view our complete portfolio of code.

One of the features of this is the ability to search for keywords in the code. A good
example of why you might want to do this is when looking for a specific P/Invoke definition,
for example CreateProcess. Doing a search on “CreateProcess” results in a reference
in OpenNETCF.Diagnostics.Process –
and we can see that on line 402 and 403 the function is declared.

To give an overview of the various namespaces, classes, structures and interfaces
which make up the OpenNETCF Smart Device Framework, I have created a poster – which
you can now download in PDF format and print out as big as you want from the
link below:-

OpenNETCF Posters

I’ll also be uploading shortly a further refresh to the online
documentation. This will hopefully fill in a few of the gaps in the documentation,
and also add details of some of the new functionality which is currently being added
to the source. Chris recently posted
the latest
source packages which include his cool
new instrumentation controls.