JAJAH Development Blog

While looking for a full article about this I found out it won’t hurt to have another quick explanation about this process.

Sometimes when creating an application you want some sort of verification about which phone is accessing your service (service-client application). A good way to do this is to use the unique device id.

Now I will explain how we do it, we are going to get a 40 char string that is hashed with an AppString we will provide which will be unique to each and every device, and will be constant for this device and AppString.

First we define the P/Invoke signature:

[DllImport("coredll.dll")]
private static extern int GetDeviceUniqueID([In, Out] byte[] appdata, int cbApplictionData,
                                            int dwDeviceIDVersion,
                                            [In, Out] byte[] deviceIDOuput, ref uint pcbDeviceIDOutput);

Now we are going to define a private static member so we don’t go through the entire process every time we need this and then create it with a public static method:

private static string s_UniqueDeviceID;

/// <summary>
/// Gets the unique device id, this is an unique id of the phone
/// which is hashed with the AppString
/// </summary>
/// <returns>a 40 characters unique id</returns>
public static string GetUniqueDeviceID()
{
    if (string.IsNullOrEmpty(s_UniqueDeviceID))
    {
        // define AppString
        string AppString = "MyAppString";

        // get the byte array for the string
        byte[] AppData = Encoding.ASCII.GetBytes(AppString);

        // some parameters for the native call
        int appDataSize = AppData.Length;
        uint SizeOut = 20;

        // our out parameter
        byte[] DeviceOutput = new byte[20];

        // Call the native GetDeviceUniqueID method from coredll.dll
        GetDeviceUniqueID(AppData, appDataSize, 1, DeviceOutput, ref SizeOut);

        // check that we got something
        if (SizeOut > 0)
        {
            // build text from received bytes
            StringBuilder resultText = new StringBuilder();
            for (int i = 0; i < DeviceOutput.Length; i++)
            {
                resultText.Append(string.Format("{0:x2}", DeviceOutput[i]));
            }

            // set up result
            s_UniqueDeviceID = resultText.ToString();
        }
    }

    return s_UniqueDeviceID;
}

As you can see the AppString can really be whatever we want it to be. the rest is a little work in order to transform it all from bytes to string but that is why we do it only once!

The only important thing I can see about the AppString is that it won’t be null\empty and that it will be constant throughout your application and usage.

Hope this was clear.

Cheers,

Nadav

Using a Native DLL (c++) in a managed (c#) project is  straightforward. you just write the following in your managed code:

[DllImport("coredll.dll")]
public static extern bool CeRunAppAtEvent(string AppName, int Event);

and use the native function like it was managed.

The problem happens when you want to write your own native dll. It seems that the function in the native code must look like this

extern "C" __declspec(dllexport) void function()

confusing a bit, since when not programming for  Windows Mobile you may also write your native function without extern "C"  and add the EntryPoint attribute, and it will work… (for Windows Mobile this is not the case, you have to make sure you write extern "C") 

This topic is one I have been spending some time studying.
How do you get your program to the foreground when a certain event accurse ?

The answer is quite simple actually, you just need to call a UI component. like:

MessageBox.Show("Show Me");

And it will show the top most form in your application. Another thing you can do is call a form with Show().

Now, for a little bonus I have for you the…

How to send it back to the background!

What we need to do here is to call Hide() on all the visible forms in our application, this will essentially cause all our UI to go to the background and will bring back the last active application.

A little hint, you might want to use what you learned, and combine it with the previous post ;].

Nadav