Correct Way to Load Assembly Find Class and Call Run Method

Question

Sample console program   class Program       static void Main string   args                       code to build dll     not written yet             Assembly assembly   Assembly LoadFile   C  dyn dll               don t know what or how to cast here            looking for a better way to do next 3 lines         IRunnable r   assembly CreateInstance  TestRunner            if  r    null  throw new Exception  broke            r Run               I want to dynamically build an assembly   dll   and then load the assembly  instantiate a class  and call the Run   method of that class  Should I try casting the TestRunner class to something  Not sure how the types in one assembly  dynamic code  would know about my types in my  static assembly   shell app   Is it better to just use a few lines of reflection code to call Run   on just an object  What should that code look like   UPDATE  William Edmondson - see comment

User · Accepted Answer

Use an AppDomain

It is safer and more flexible to load the assembly into its own AppDomain first.

So instead of the answer given previously:

var asm = Assembly.LoadFile(@"C:\myDll.dll");
var type = asm.GetType("TestRunner");
var runnable = Activator.CreateInstance(type) as IRunnable;
if (runnable == null) throw new Exception("broke");
runnable.Run();

I would suggest the following (adapted from this answer to a related question):

var domain = AppDomain.CreateDomain("NewDomainName");
var t = typeof(TypeIWantToLoad);
var runnable = domain.CreateInstanceFromAndUnwrap(@"C:\myDll.dll", t.Name) as IRunnable;
if (runnable == null) throw new Exception("broke");
runnable.Run();

Now you can unload the assembly and have different security settings.

If you want even more flexibility and power for dynamic loading and unloading of assemblies, you should look at the Managed Add-ins Framework (i.e. the System.AddIn namespace). For more information, see this article on Add-ins and Extensibility on MSDN.

User · Answer

I m doing exactly what you re looking for in my rules engine  which uses CS-Script for dynamically compiling  loading  and running C   It should be easily translatable into what you re looking for  and I ll give an example  First  the code  stripped-down    using System  using System Collections Generic  using System IO  using System Linq  using System Reflection  using CSScriptLibrary   namespace RulesEngine            lt summary gt          Make sure  lt typeparamref name  T   gt  is an interface  not just any type of class                   Should be enforced by the compiler  but just in case it s not  here s your warning           lt  summary gt           lt typeparam name  T  gt  lt  typeparam gt      public class RulesEngine lt T gt  where T   class               public RulesEngine string rulesScriptFileName  string classToInstantiate                this                         if  rulesScriptFileName    null  throw new ArgumentNullException  rulesScriptFileName                if  classToInstantiate    null  throw new ArgumentNullException  classToInstantiate                 if   File Exists rulesScriptFileName                                 throw new FileNotFoundException  Unable to find rules script   rulesScriptFileName                              RulesScriptFileName   rulesScriptFileName              ClassToInstantiate   classToInstantiate               LoadRules                       public T  Interface           public string RulesScriptFileName   get  private set            public string ClassToInstantiate   get  private set            public DateTime RulesLastModified   get  private set             private RulesEngine                          Interface   null                     private void LoadRules                         if   File Exists RulesScriptFileName                                 throw new FileNotFoundException  Unable to find rules script   RulesScriptFileName                              FileInfo file   new FileInfo RulesScriptFileName                DateTime lastModified   file LastWriteTime               if  lastModified    RulesLastModified                                   No need to load the same rules twice                  return                             string rulesScript   File ReadAllText RulesScriptFileName                Assembly compiledAssembly   CSScript LoadCode rulesScript  null  true                 Interface   compiledAssembly CreateInstance ClassToInstantiate  AlignToInterface lt T gt                  RulesLastModified   lastModified                      This will take an interface of type T  compile a  cs file into an assembly  instantiate a class of a given type  and align that instantiated class to the T interface  Basically  you just have to make sure the instantiated class implements that interface  I use properties to setup and access everything  like so   private RulesEngine lt IRulesEngine gt  rulesEngine   public RulesEngine lt IRulesEngine gt  RulesEngine       get               if  null    rulesEngine                        string rulesPath   Path Combine Application StartupPath   Rules cs                 rulesEngine   new RulesEngine lt IRulesEngine gt  rulesPath  typeof Rules  FullName                      return rulesEngine           public IRulesEngine RulesEngineInterface       get   return RulesEngine Interface        For your example  you want to call Run    so I d make an interface that defines the Run   method  like this   public interface ITestRunner       void Run        Then make a class that implements it  like this   public class TestRunner   ITestRunner       public void Run                    implementation goes here           Change the name of RulesEngine to something like TestHarness  and set your properties   private TestHarness lt ITestRunner gt  testHarness   public TestHarness lt ITestRunner gt  TestHarness       get               if  null    testHarness                        string sourcePath   Path Combine Application StartupPath   TestRunner cs                 testHarness   new TestHarness lt ITestRunner gt  sourcePath   typeof TestRunner  FullName                      return testHarness           public ITestRunner TestHarnessInterface       get   return TestHarness Interface        Then  anywhere you want to call it  you can just run   ITestRunner testRunner   TestHarnessInterface   if  null    testRunner        testRunner Run        It would probably work great for a plugin system  but my code as-is is limited to loading and running one file  since all of our rules are in one C  source file  I would think it d be pretty easy to modify it to just pass in the type source file for each one you wanted to run  though  You d just have to move the code from the getter into a method that took those two parameters   Also  use your IRunnable in place of ITestRunner

User · Answer

When you build your assembly  you can call AssemblyBuilder SetEntryPoint  and then get it back from the Assembly EntryPoint property to invoke it   Keep in mind you ll want to use this signature  and note that it doesn t have to be named Main   static void Run string   args

User · Answer

You will need to use reflection to get the type  TestRunner   Use the Assembly GetType method   class Program       static void Main string   args                Assembly assembly   Assembly LoadFile   C  dyn dll            Type type   assembly GetType  TestRunner            var obj    TestRunner Activator CreateInstance type           obj Run

User · Answer

If you do not have access to the TestRunner type information in the calling assembly  it sounds like you may not   you can call the method like this    Assembly assembly   Assembly LoadFile   C  dyn dll    Type     type       assembly GetType  TestRunner    var      obj        Activator CreateInstance type       Alternately you could get the MethodInfo for the TestRunner Run method type InvokeMember  Run                      BindingFlags Default   BindingFlags InvokeMethod                     null                    obj                    null     If you have access to the IRunnable interface type  you can cast your instance to that  rather than the TestRunner type  which is implemented in the dynamically created or loaded assembly  right       Assembly assembly    Assembly LoadFile   C  dyn dll      Type     type        assembly GetType  TestRunner      IRunnable runnable   Activator CreateInstance type  as IRunnable    if  runnable    null  throw new Exception  broke      runnable Run

[c#] Correct Way to Load Assembly, Find Class and Call Run() Method

Use an AppDomain

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