Listing 4 A better base class for implementing a custom license provider

using System;
using System.ComponentModel;

public abstract class CustomLicenseProvider : LicenseProvider
{
    public override License GetLicense(LicenseContext context, Type type, 
        object instance, bool allowExceptions)
    {
        // Step 1: locate the license key
        string licenseKey = null;
        switch ( context.UsageMode )
        {
            case LicenseUsageMode.Designtime:
                licenseKey = GetDesignTimeLicenseKey(type);
                context.SetSavedLicenseKey( type, licenseKey );
                break;
            case LicenseUsageMode.Runtime:
                licenseKey = context.GetSavedLicenseKey( type, null );
                break;
        }
        if ( licenseKey == null )
        {
            if ( allowExceptions ) throw new LicenseException(type, instance, 
                                    "No appropriate license key was located.");
            else return null;
        }


        // Step 2: validate the license key
        bool isValid = IsLicenseKeyValid( type, licenseKey );
        if ( !isValid )
        {
            if ( allowExceptions ) throw new LicenseException(type, instance, 
                                        "License key is not valid.");
            else return null;
        }


        // Step 3: grant a license        
        License license = CreateLicense(type, licenseKey);
        if ( license == null )
        {
            if ( allowExceptions ) throw new LicenseException(type, instance, 
                                       "license could not be created.");
            else return null;
        }

        return license;
    }

    protected abstract string GetDesignTimeLicenseKey(Type type);
    protected abstract bool IsLicenseKeyValid(Type type, string licenseKey);
    protected abstract License CreateLicense(Type type, string licenseKey);
}