private String[] DiscoverPluginAssembliesHelper(
String path, PluginCriteria criteria, Type criteriaType)
{
String[] assemblies;
// Get .dll names
path = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, path);
assemblies = Directory.GetFiles(path, "*.dll");
if(assemblies.Length != 0){
ArrayList assembliesIncluded = new ArrayList();
foreach(String s in assemblies){
// Load the assembly
Assembly assembly = Assembly.LoadFrom(s);
// Find matching type?
Type[] types = assembly.GetTypes();
foreach(Type t in types){
if(IncludeType(t, criteria, criteriaType)){
assembliesIncluded.Add(s);
break; // match found, move on
}
}
}
// Get array of matching assemblies
assemblies = (String[])assembliesIncluded.ToArray(
typeof(String));
}
return assemblies;
}
// Test a type for matching the plugin criteria
private static Boolean IncludeType(
Type type, PluginCriteria criteria, Type criteriaType)
{
Boolean judgement = false;
// Switch on criteria type
switch(criteria){
case PluginCriteria.Interface: // interface
if(!criteriaType.IsInterface){
throw new ArgumentException(
"Criteria does not match criteria type.");
}
// If compatible with the interface type, thumbs-up
judgement = criteriaType.IsAssignableFrom(type);
break;
case PluginCriteria.BaseClass:
if(!(criteriaType.IsClass && !criteriaType.IsSealed)){
throw new ArgumentException(
"Criteria does not match criteria type.");
}
// If compatible with the base type, thumbs-up
judgement = criteriaType.IsAssignableFrom(type);
break;
case PluginCriteria.CustomAttribute:
if(!typeof(Attribute).IsAssignableFrom(criteriaType)){
throw new ArgumentException(
"Criteria does not match criteria type.");
}
// If the attribute is defined on the type, then true
judgement = type.IsDefined(criteriaType, true);
break;
default:
throw new ArgumentException("Invalid plugin criteria.");
}
return judgement;
}
// From an array of assemblies find the plugin types
private static Type[] LoadPluginTypesHelper(
String[] assemblies, PluginCriteria criteria, Type criteriaType)
{
ArrayList typesIncluded = new ArrayList();
foreach(String s in assemblies){
// Load the assembly
Assembly assembly = Assembly.LoadFrom(s);
// Find the plugin types
Type[] types = assembly.GetExportedTypes();
foreach(Type t in types){
if(IncludeType(t, criteria, criteriaType)){
typesIncluded.Add(t);
}
}
}
// Return an array of types
return (Type[])typesIncluded.ToArray(typeof(Type));
}
// Get an array of plugin types using a
// plugin criteria and trust level
public static Type[] LoadPluginTypes(
PluginTrustLevel level, PluginCriteria criteria, Type criteriaType)
{
// Build the path for plugins we are searching for
// also, if secure plugins won't work, throw
String pluginPath;
if(level == PluginTrustLevel.Full){
pluginPath = fullTrustPath;
}else{
if(!supportSecurePlugins){
throw new SecurityException(
"Semi-trusted plugins were not enabled!");
}
pluginPath = semiTrustPath;
}
// Create a temporary app domain so that we can unload assemblies
AppDomain domain =
AppDomain.CreateDomain("TempDom"+Guid.NewGuid().ToString());
// Find the name of this assembly and load it into the domain
String assemblyName = Assembly.GetExecutingAssembly().FullName;
domain.Load(assemblyName);
// Create an instance of the PluginManager type
// in the temporary domain
BindingFlags binding = BindingFlags.CreateInstance |
BindingFlags.NonPublic | BindingFlags.Instance;
ObjectHandle handle = domain.CreateInstance(
assemblyName, typeof(PluginManager).ToString(), false,
binding, null, null, null, null, null);
PluginManager helper = (PluginManager)handle.Unwrap();
try{
// Get an array of assemblies that include matching plugins
String[] assemblies= helper.DiscoverPluginAssembliesHelper(
pluginPath, criteria, criteriaType);
// return loaded plugin types
return LoadPluginTypesHelper(assemblies, criteria, criteriaType);
}catch(ReflectionTypeLoadException){
return new Type[0];
}finally{
// Unload any unwanted assemblies
AppDomain.Unload(domain);
}
}
