Test if DWORD value exists in registry using C#

Question

I have a Win Forms application that among other things, moves a PC to a new OU then writes a DWORD value to the registry to indicate whether the move succeeded or failed. It reboots the PC after the rest of the operations complete. Upon reboot the application re-launches itself and checks registry values for what was successful and what was not, and displays 'checks' or 'X's on the form.

I am wondering how I can test to see if the DWORD value exists, then read whether it is a '1' or not. I realize I can just make this easy on myself and just have the application write a string value, but I am trying to learn.

Using Visual Studio I receive a warning when I try to check if the DWORD value is null I get the following warning: The result of the expression is always true since a value of type int is never equal to null of type int

Ok, so an int value cannot be null, so how else could I test to see if it exists in the registry to avoid an exception? See my code below.

RegistryKey domainJoin = Registry.LocalMachine.OpenSubKey
                   (@"SOFTWARE\SHIELDING\5", RegistryKeyPermissionCheck.ReadWriteSubTree);


    //If the domain join was attempted, check outcome...
            if (domainJoin != null)
            {
                //Check if move to OU was successful
                int ouMoveVal = (int)domainJoin.GetValue("movePC");
                if (ouMoveVal != null) <-----HERE IS WHERE I GET THE WARNING
                {
                    //If PC move to new OU was successful
                    //show 'check' mark
                    if (ouMoveVal == 1)
                    {
                        picChkOU.Visible = true;
                    }
                    //If PC move to new OU was NOT successful
                    //show 'X' mark
                    else
                    {
                        picXOU.Visible = true;
                    }
                }

Answer 1

You could do something like this using a nullable int -- ie int? -- and the GetValue overload that takes a default value if the reg value doesn't exist:

int? ouMoveVal = (int?) domainJoin.GetValue("movePC", new int?());

if (ouMoveVal.HasValue)

More on nullable: https://msdn.microsoft.com/en-us/library/b3h38hb0%28v=vs.110%29.aspx?f=255&MSPPError=-2147217396

Answer 2

Change the order of the check so the object is checked for null before you cast it to an int :

//Check if move to OU was successful
object ouMoveVal = domainJoin.GetValue("movePC");

if (ouMoveVal != null)
{
    // try to convert to int here and continue...

This means you benefit from the information provided by a null object returned, indicating the key does not exist.

Then you can Int32.TryParse to see if it's an int after the null check.

Answer 3

Another solution...

using Microsoft.Win32;

private static int ReadRegistryIntValue(string sSubKey, string sKeyName)
{
    try
    {
        int retValue = 0;
        RegistryKey rkSearchFor = Registry.LocalMachine.OpenSubKey(sSubKey);
        if (rkSearchFor == null)
        {
            return retValue;
        }
        else
        {
            try
            {
                retValue = Convert.ToInt32(rkSearchFor.GetValue(sKeyName));
            }
            catch (Exception)
            {
                return 0;
            }
            finally
            {
                rkSearchFor.Close();
                rkSearchFor.Dispose();
            }
        }
        return retValue;
    }
    catch (Exception)
    {
        return 0;
    }
}