function Set-RegistryKey_AppInstalled
{
    <#
        .SYNOPSIS
         Detection Method for successful installed program.
        .DESCRIPTION
         Creates a registry key under HKLM\software\RM\AppStatus. The Key value is set to "Installed" or "Uninstalled"
         The Variables are from the Deploy-Application.ps1 script.
         The Function Call has to be made in the POST INSTALLATION part.

         If UninstallOldVersions does not work, you are most likly not complying with the naming standard.
        .PARAMETER Uninstall
            Switch parameter to set the application as uninstalled
        .PARAMETER Remove
            Switch parameter to remove the key, use the Uninstall parameter instead.
        .PARAMETER UninstallOldVersions
            Switch parameter to set the all old versions of the application as uninstalled
            Normaly set in PRE-INSTALLATION after the removal of old versions
        .EXAMPLE
         Set-registryKey_AppInstalled

         Set-registryKey_AppInstalled -Uninstall

         Set-registryKey_AppInstalled -UninstallOldVersions
        .LINK
         http://psappdeploytoolkit.com/
    #>
    [CmdletBinding(DefaultParameterSetName = "Uninstalled", SupportsShouldProcess = $True)]
    Param (
        [parameter(Mandatory = $false, ParameterSetName = "Uninstalled")]
        [switch]$Uninstall,
        [parameter(Mandatory = $false, ParameterSetName = "Remove")]
        [switch]$Remove,
        [parameter(Mandatory = $false, ParameterSetName = "UninstallOldVersions")]
        [switch]$UninstallOldVersions
    )

    Initialize-ADTFunction -Cmdlet $PSCmdlet -SessionState $ExecutionContext.SessionState
    $AppVendor = $adtSession.AppVendor
    $AppName = $adtSession.AppName
    $AppVersion = $adtSession.AppVersion
    $AppRevision = $adtSession.AppRevision

    if ($Uninstall)
    {
        Write-ADTLogEntry -Message "Writing registry detection Method for successful Uninstalled program" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'
        if (-not (Test-path -Path "HKLM:\SOFTWARE\RM\AppStatus")) { New-Item -Path "HKLM:\SOFTWARE\RM\AppStatus" }
        Set-ItemProperty -Path "HKLM:\SOFTWARE\RM\AppStatus" -Name "$AppVendor $AppName $AppVersion $AppRevision" -Value "Uninstalled"
        Write-ADTLogEntry -Message "Registry -> $AppVendor $AppName $AppVersion $AppRevision=Uninstalled" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'

    }
    elseif ($Remove)
    {
        Write-ADTLogEntry -Message "Deleting registry detection Method for program" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'
        Remove-ItemProperty -Path "HKLM:\SOFTWARE\RM\AppStatus" -Name "$AppVendor $AppName $AppVersion $AppRevision" -ErrorAction SilentlyContinue
        Write-ADTLogEntry -Message "Registry -> $AppVendor $AppName $AppVersion $AppRevision" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'
    }
    elseif ($UninstallOldVersions)
    {
        Write-ADTLogEntry -Message "Writing registry detection Method for successful Uninstalled old versions of the program" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'
        $AppCount = 0
        $AppStatus = Get-RegistryKey -Key "HKLM:SOFTWARE\RM\AppStatus"
        foreach ($item in $AppStatus.PSObject.Properties)
        {
            if ($item.name -like "$AppVendor $AppName *")
            {
                if ($item.Value -eq "Installed" -and $item.Name -notlike "$AppVendor $AppName $AppVersion $AppRevision")
                {
                    Set-ItemProperty -Path "HKLM:\SOFTWARE\RM\AppStatus" -Name $item.name -Value "Uninstalled"
                    Write-ADTLogEntry -Message "Registry -> $($item.name)=Uninstalled" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'
                    $AppCount++
                }
            }
        }
        if ($AppCount -eq 0)
        {
            Write-ADTLogEntry -Message "No old application detection rule found" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'
        }
        elseif ($AppCount -eq 1)
        {
            Write-ADTLogEntry -Message "1 detection rule set to uninstalled" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'
        }
        else
        {
            Write-ADTLogEntry -Message "$AppCount detection rules set to uninstalled" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'
        }
    }
    else
    {
        Write-ADTLogEntry -Message "Writing registry detection Method for successful installed program" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'
        if (-not (Test-path -Path "HKLM:\SOFTWARE\RM")) { New-Item -Path "HKLM:\SOFTWARE\RM" }
        if (-not (Test-path -Path "HKLM:\SOFTWARE\RM\AppStatus")) { New-Item -Path "HKLM:\SOFTWARE\RM\AppStatus" }
        Set-ItemProperty -Path "HKLM:\SOFTWARE\RM\AppStatus" -Name "$AppVendor $AppName $AppVersion $AppRevision" -Value "Installed"
        Write-ADTLogEntry -Message "Registry -> $AppVendor $AppName $AppVersion $AppRevision=Installed" -Source 'Set-RegistryKey_AppInstalled' -LogType 'CMTrace'
    }
}