Plugin loading problem

I keep getting this error on the following code when I attempt to load my plugins from the Plugins folder. If I move my plugins out of the Plugin folder and into the Application.StartupPath, the problem disappears. In other words, if I try to load the plugins from c:\utils\C#\WinZm\bin\Debug\Plugins, the app generates the error. But if I load them from c:\utils\C#\WinZm\Bin\Debug (the ApplicationStartupPath) the plugins load without any problem. Any suggestions for a resolution?

Attachment 7096

Code:

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private void Form1_Load(object sender, System.EventArgs e)
        {
            string path = Application.StartupPath + @"\Plugins";
            //string path = "C:\\utils\\C#\\WinZM\\bin\\Debug";
            MessageBox.Show(path);
            string[] pluginFiles = Directory.GetFiles(path, "*.dll");
            ipi = new IPlugin[pluginFiles.Length];
            for (int i = 0; i < pluginFiles.Length; i++)
            {
                string args = pluginFiles[i].Substring(
                    pluginFiles[i].LastIndexOf("\\") + 1,
                    pluginFiles[i].IndexOf(".dll") -
                    pluginFiles[i].LastIndexOf("\\") - 1);
                Type ObjType = null;
                try
                {
                    // load it
                    Assembly ass = null;
                    ass = Assembly.Load(args);
                    if (ass != null)
                    {
                        ObjType = ass.GetType(args + ".PlugIn");
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
                try
                {
                    // Create the object as we have the Report Type
                    if (ObjType != null)
                    {
                        ipi[i] = (IPlugin)Activator.CreateInstance(ObjType);
                        ipi[i].Host = this;
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
            }
        }

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Why don't you keep the full path of the DLL? Without it, it just follows DLL lookup rules, and your plugin folder apparently isn't in the search path.

Quote:

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Why don't you keep the full path of the DLL? Without it, it just follows DLL lookup rules, and your plugin folder apparently isn't in the search path.

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I tried a full path for the dll and it generates the following error:
Attachment 7101

I remember coming across a site that explained a quirk with the Assembly Load method a while back when I was Googling for plugin info. I didn't pay much attention to the site because at the time I didn't have any plugin code. Now I just can't find that site.

Ahh, found it!!! The problem is that the Load method uses the Framework discovery rules. I.e., the Global Assembly Cache (GAC), the path in the app's manifest, the directory where your app resides etc. If the plugin is outside of the discovery rules, as in my case where it was located below the app's directory, it will not load. The solution is to use the LoadFile method which will always load the path requested.

Code:

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private void Form1_Load(object sender, System.EventArgs e)
        {
            string args1;
            string path = Application.StartupPath + @"\Plugins\";
            string[] pluginFiles = Directory.GetFiles(path, "*.dll");
            ipi = new IPlugin[pluginFiles.Length];
       
            for (int i = 0; i < pluginFiles.Length; i++)
            {
                    string args = pluginFiles[i].Substring(
                    pluginFiles[i].LastIndexOf("\\") + 1,
                    pluginFiles[i].IndexOf(".dll") -
                    pluginFiles[i].LastIndexOf("\\") - 1);
                    Type ObjType = null;
                try
                {
                    Assembly asm;
                    args1 = path + args + ".dll";
                    asm = Assembly.LoadFile(args1);
                    Type[] types = asm.GetTypes();

                    if (asm != null)
                    {
                        ObjType = asm.GetType(args + ".PlugIn");
                            ipi[i] = (IPlugin)Activator.CreateInstance(ObjType);
                            ipi[i].Host = this;
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.ToString());
                }
            }
        }

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