Zack Zack - 9 months ago 60
C# Question

Writing C# Plugin System

I'm trying to write a plugin system to provide some extensibility to an application of mine so someone can write a plugin(s) for the application without touching the main application's code (and risk breaking something).

I've got the base "IPlugin" interface written (atm, nothing is implemented yet)

Here is how I'm loading:

public static void Load()
{
// rawr: http://www.codeproject.com/KB/cs/c__plugin_architecture.aspx
String[] pluginFiles = Directory.GetFiles(Plugins.PluginsDirectory, "*.dll");
foreach (var plugin in pluginFiles)
{
Type objType = null;
try
{
//Assembly.GetExecutingAssembly().GetName().Name
MessageBox.Show(Directory.GetCurrentDirectory());
Assembly asm = Assembly.Load(plugin);
if (asm != null)
{
objType = asm.GetType(asm.FullName);
if (objType != null)
{
if (typeof(IPlugin).IsAssignableFrom(objType))
{
MessageBox.Show(Directory.GetCurrentDirectory());
IPlugin ipi = (IPlugin)Activator.CreateInstance(objType);
ipi.Host = Plugins.m_PluginsHost;
ipi.Assembly = asm;
}
}
}
}
catch (Exception e)
{
MessageBox.Show(e.ToString(), "Unhandled Exception! (Please Report!)", System.Windows.Forms.MessageBoxButtons.OK, System.Windows.Forms.MessageBoxIcon.Information);
}
}
}


A friend tried to help but I really didn't understand what was wrong.

The folder structure for plugins is the following:

\

\Plugins\


All plugins reference a .dll called "Lab.Core.dll" in the [root] directory and it is not present in the Plugins directory because of duplicate references being loaded.

The plugin system is loaded from Lab.Core.dll which is also referenced by my executable. Type "IPlugin" is in Lab.Core.dll as well. Lab.Core.dll is, exactly as named, the core of my application.

EDIT:

Question: Why/What is that exception I'm getting and how could I go about fixing it?

FINAL EDIT:

Ok so I decided to re-write it after looking at some source code a friend wrote for a TF2 regulator.

Here's what I got and it works:

public class TestPlugin : IPlugin {
#region Constructor

public TestPlugin() {
//
}

#endregion

#region IPlugin Members

public String Name {
get {
return "Test Plugin";
}
}

public String Version {
get {
return "1.0.0";
}
}

public String Author {
get {
return "Zack";
}
}

public Boolean OnLoad() {
MessageBox.Show("Loaded!");
return true;
}

public Boolean OnAllLoaded() {
MessageBox.Show("All loaded!");
return true;
}

#endregion
}

public static void Load(String file) {
if (!File.Exists(file) || !file.EndsWith(".dll", true, null))
return;

Assembly asm = null;

try {
asm = Assembly.LoadFile(file);
} catch (Exception) {
// unable to load
return;
}

Type pluginInfo = null;
try {
Type[] types = asm.GetTypes();
Assembly core = AppDomain.CurrentDomain.GetAssemblies().Single(x => x.GetName().Name.Equals("Lab.Core"));
Type type = core.GetType("Lab.Core.IPlugin");
foreach (var t in types)
if (type.IsAssignableFrom((Type)t)) {
pluginInfo = t;
break;
}

if (pluginInfo != null) {
Object o = Activator.CreateInstance(pluginInfo);
IPlugin plugin = (IPlugin)o;
Plugins.Register(plugin);
}
} catch (Exception) {
}
}

public static void LoadAll() {
String[] files = Directory.GetFiles("./Plugins/", "*.dll");
foreach (var s in files)
Load(Path.Combine(Environment.CurrentDirectory, s));

for (Int32 i = 0; i < Plugins.List.Count; ++i) {
IPlugin p = Plugins.List.ElementAt(i);
try {
if (!p.OnAllLoaded()) {
Plugins.List.RemoveAt(i);
--i;
}
} catch (Exception) {
Plugins.List.RemoveAt(i);
--i;
}
}
}

Answer Source

It sounds like you have a circular reference. You said your plugins reference Lab.Core.DLL, but you also say the plugins are loaded from Lab.Core.DLL.

Am I misunderstanding what is happening here?

EDIT: OK now that you have added your question to the question...

You need to have Lab.Core.DLL accessible to the plugin being loaded since it is a dependency. Normally that would mean having it in the same directory or in the GAC.

I suspect there are deeper design issues at play here, but this is your immediate problem.

Recommended from our users: Dynamic Network Monitoring from WhatsUp Gold from IPSwitch. Free Download