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C# programmatically edit my .NET assembly at runtime

I have a .NET assembly that is built by me but would like to be able rewrite the .DLL with some minor but arbitrary attribute change file at runtime. Specifically I would like to be able to change a property of an attribute of a class so that I can customize the binary depending on the situation.
To illustrate, I want to achieve the effect of editing the assembly being generated from the code
[SomeAttribute("Name")]
public class MyClass{
...
such that the new assembly is functionally the same as
[SomeAttribute("Custom Name")]
public class MyClass{
...
And this "Custom Name" could be anything (determined at runtime). Is this possible to do at runtime?
The reason why the actual .DLL needs to be modified is because it will get loaded up by a seperate process which cannot determine the runtime information (I do not control this process).
Experimentation so far has shown that it seems to work if the new "Custom Name" is the same length as the original, but not otherwise (even if you edit the preceding byte that specifies the length; presumably there are offsets stored in the file somewhere).
EDIT: Forgot to mention, solution needs to be under the .NET 2 framework as well.

Unclear what you really want to do (XY problem?)
Still, if you want to modify an assembly, you normally use Mono.Cecil that self-describes as: you can load existing managed assemblies, browse all the contained types, modify them on the fly and save back to the disk the modified assembly. .
Note that an attribute can contain extra data on top of the data that is passed as a parameter:
public class MyAttribute : Attribute
{
public MyAttribute(string str)
{
argument = str;
}
private string argument;
public string Argument { get; }
public string AssemblyName
{
get
{
return Assembly.GetEntryAssembly().FullName;
}
}
}
[MyAttribute("Hello")]
class Program
{
static void Main(string[] args)
{
var attr = typeof(Program).GetCustomAttribute<MyAttribute>();
Console.WriteLine(attr.Argument);
Console.WriteLine(attr.AssemblyName);
}
}

Using the extremely helpful suggestion from #xanatos I have made this solution:
Under .NET 2, you can install package Mono.Cecil 0.9.6.1.
The code then is as follows:
AssemblyDefinition assbDef = AssemblyDefinition.ReadAssembly("x.dll");
TypeDefinition type = assbDef.MainModule.GetType("NameSpace.MyClass").Resolve();
foreach (CustomAttribute attr in type.CustomAttributes)
{
TypeReference argTypeRef = null;
int? index = null;
for (int i = 0; i < attr.ConstructorArguments.Count; i++)
{
CustomAttributeArgument arg = attr.ConstructorArguments[i];
string stringValue = arg.Value as string;
if (stringValue == "Name")
{
argTypeRef = arg.Type;
index = i;
}
}
if (index != null)
{
attr.ConstructorArguments[(int)index] = new CustomAttributeArgument(argTypeRef, newName);
}
}
assbDef.Write("y.dll");
Which will search an assembly for any attribute arguments with value "Name" and replace their value with newName.

Rather than modifying the DLL, you can add attributes at run-time using the TypeDescriptor class; e.g.
TypeDescriptor.AddAttributes(typeof(MyClass), new SomeAttribute("Custom Name"));
The only caveat with this approach is that code which relies purely on reflection will not be able to read the added attribute(s) - you must use TypeDescriptor.GetAttributes(). However, most of the built-in .NET Framework methods that operate on attributes are aware of metadata added at run-time.
https://msdn.microsoft.com/en-us/library/system.componentmodel.typedescriptor_methods(v=vs.110).aspx

Get methods and attributes from dll assembly

I'm trying to get a small plugin mechanism running by reflecting an dll file providing my class Plugin (implementing my Plugin-Interface shared among dll and main project / sorry for naming both the same) offering an attribute of type string and a main-method activate:
Interface:
public interface Plugin
{
string pluginName{get;set;}
void activate(System.Windows.Forms.Form main);
}
dll class:
public class Plugin : WhiteA.Plugin
{
public string pluginName{get;set;}
public void activate(System.Windows.Forms.Form main){
//find the right form to modify it
IEnumerable<System.Windows.Forms.ComboBox> ie= GetControlsOfType<System.Windows.Forms.ComboBox>(main);
System.Windows.Forms.ComboBox cb=GetControlsOfType<System.Windows.Forms.ComboBox>(main).FirstOrDefault();
cb.Items.Add("Modification");
System.Windows.Forms.MessageBox.Show(cb.SelectedItem.ToString());
}
public static IEnumerable<T> GetControlsOfType<T>(System.Windows.Forms.Control root)
where T : System.Windows.Forms.Control
{
var t = root as T;
if (t != null)
yield return t;
var container = root as System.Windows.Forms.ContainerControl;
if (container != null)
foreach (System.Windows.Forms.Control c in container.Controls)
foreach (var i in GetControlsOfType<T>(c))
yield return i;
}
}
So here comes the problem, there is no type named "Plugin" to be found in the assembly. Tried to get all types from all assemblies in the directory, get all methods/members/custom attributes from them, have them logged etc, but there is nothing of my class Plugin to be found, while the dll definitely is being found, as it doesn't return the MessageBox.
string[] files=new string[]{};
string path="Error retrieving path";
try{
path = System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location);
files = System.IO.Directory.GetFiles(path, "*.dll");
}catch(Exception exF){
}
if(files.Length>0){
foreach (string dll in files){
try{
System.Reflection.Assembly sampleAssembly = System.Reflection.Assembly.LoadFrom(dll);
Type myType = sampleAssembly.GetType("Plugin");
System.Reflection.MethodInfo method = myType.GetMethod("activate");
object myInstance = Activator.CreateInstance(myType);
method.Invoke(myInstance, new object[]{this});
}catch(Exception exL){
}
}
}else{
MessageBox.Show("No working plugins detected in " + path.ToString(), "Nothing to activate", MessageBoxButtons.OK, MessageBoxIcon.Exclamation, MessageBoxDefaultButton.Button1);
}
I know my code probably looks really messy to you all - I think the last try-block is the only thing relevant here, wanted to put in the class itself and the interface for a little bit transparency though - and my english isn't perfect, but I hope someone can help me out finding my attribute+method in the assembly.
EDIT:
try{
System.Reflection.Assembly sampleAssembly = System.Reflection.Assembly.LoadFrom(dll);
List<Type> list= sampleAssembly.GetTypes().Where(p =>
p.Namespace == dll &&
p.Name.Contains("Plugin")
).ToList();
Type myType=list.FirstOrDefault();
//Type myType = sampleAssembly.GetType("Plugin");
System.Reflection.MethodInfo method = myType.GetMethod("activate");
object myInstance = Activator.CreateInstance(myType);
method.Invoke(myInstance, new object[]{this});
}
I did change it according to Getting all types in a namespace via reflection
Still the same result, what did I do wrong?

As pointed out by #stuartd:
Type myType = sampleAssembly.GetType("WhiteA_Plugin_PausedVideo.Plugin");
is the solution, missed the namespace
cb.Items.Add("Modification");
doesn't work though...any suggestions?
Got it to work getting the form's children by Controls["nameOfChild"] directly, that help method to fetch all objects by class seems to be wrong here.
Plugin works now, thanks!

Is there a better way to check if a project is NUnit or MSTest based?

I want to check if a c# project is NUnit or MSTest based. Currently, I read csproj's file and look for a specific string like below.
const string MSTEST_ELEMENT = "<TestProjectType>UnitTest</TestProjectType>";
const string NUNIT_ELEMENT = #"<Reference Include=""nunit.framework"">";
var file = File.ReadAllText("C:\myfile.csproj");
if (file.Contains(NUNIT_ELEMENT))
{
result = TestProjectType.NUnit;
}
else if (file.Contains(MSTEST_ELEMENT))
{
result = TestProjectType.MSTest;
}
It works as I expected but looking for a specific text in a file is ugly for me. Is there a better way to do this?

Check the solution for dll reference "NUnit.framework.dll" . For NUnit, it is neccesary to provide reference of that dll.

You could use a reflection-based approach - load the DLL from the test project, get all of the public types in it, and check for [TestClass] attributes to indicate if it's MSTest, etc.
This sample (works but not really tested) gives an example. You could make it better by referencing the test attribute types in whatever runs this code so you could do proper type comparisons instead of strings.
class Program
{
static void Main(string[] args)
{
var path = #"Path\To\Your\Test\Dll";
//load assembly:
var assembly = Assembly.LoadFile(path);
//get all public types:
var types = assembly.GetExportedTypes();
foreach (var t in types)
{
Console.WriteLine(t.Name);
//check for [TestClass] attribute:
var attributes = t.GetCustomAttributes();
foreach (var attr in attributes)
{
var typeName = attr.TypeId.ToString();
Console.WriteLine(attr.TypeId);
if (typeName== "Microsoft.VisualStudio.TestTools.UnitTesting.TestClassAttribute")
{
Console.WriteLine("It's MSTest");
}
else if (typeName == "Nunit.Tests.TestFixture") //not sure if that's the right type id :)
{
Console.WriteLine("It's NUnit");
}
else
{
Console.WriteLine("I Have no idea what it is");
}
}
}
Console.ReadLine();
}
}

.NET assemblies: understanding type visibility

I am trying to reproduce something that System.Xml.Serialization already does, but for a different source of data.
For now task is limited to deserialization only.
I.e. given defined source of data that I know how to read. Write a library that takes a random type, learns about it fields/properties via reflection, then generates and compiles "reader" class that can take data source and an instance of that random type and writes from data source into the object's fields/properties.
here is a simplified extract from my ReflectionHelper class
public class ReflectionHelper
{
public abstract class FieldReader<T>
{
public abstract void Fill(T entity, XDataReader reader);
}
public static FieldReader<T> GetFieldReader<T>()
{
Type t = typeof(T);
string className = GetCSharpName(t);
string readerClassName = Regex.Replace(className, #"\W+", "_") + "_FieldReader";
string source = GetFieldReaderCode(t.Namespace, className, readerClassName, fields);
CompilerParameters prms = new CompilerParameters();
prms.GenerateInMemory = true;
prms.ReferencedAssemblies.Add("System.Data.dll");
prms.ReferencedAssemblies.Add(Assembly.GetExecutingAssembly().GetModules(false)[0].FullyQualifiedName);
prms.ReferencedAssemblies.Add(t.Module.FullyQualifiedName);
CompilerResults compiled = new CSharpCodeProvider().CompileAssemblyFromSource(prms, new string[] {source});
if (compiled.Errors.Count > 0)
{
StringWriter w = new StringWriter();
w.WriteLine("Error(s) compiling {0}:", readerClassName);
foreach (CompilerError e in compiled.Errors)
w.WriteLine("{0}: {1}", e.Line, e.ErrorText);
w.WriteLine();
w.WriteLine("Generated code:");
w.WriteLine(source);
throw new Exception(w.GetStringBuilder().ToString());
}
return (FieldReader<T>)compiled.CompiledAssembly.CreateInstance(readerClassName);
}
private static string GetFieldReaderCode(string ns, string className, string readerClassName, IEnumerable<EntityField> fields)
{
StringWriter w = new StringWriter();
// write out field setters here
return #"
using System;
using System.Data;
namespace " + ns + #".Generated
{
public class " + readerClassName + #" : ReflectionHelper.FieldReader<" + className + #">
{
public void Fill(" + className + #" e, XDataReader reader)
{
" + w.GetStringBuilder().ToString() + #"
}
}
}
";
}
}
and the calling code:
class Program
{
static void Main(string[] args)
{
ReflectionHelper.GetFieldReader<Foo>();
Console.ReadKey(true);
}
private class Foo
{
public string Field1 = null;
public int? Field2 = null;
}
}
The dynamic compilation of course fails because Foo class is not visible outside of Program class. But! The .NET XML deserializer somehow works around that - and the question is: How?
After an hour of digging System.Xml.Serialization via Reflector I came to accept that I lack some kind of basic knowledge here and not really sure what am I looking for...
Also it is entirely possible that I am reinventing a wheel and/or digging in a wrong direction, in which case please do speak up!

You don’t need to create a dynamic assembly and dynamically compile code in order to deserialise an object. XmlSerializer does not do that either — it uses the Reflection API, in particular it uses the following simple concepts:
Retrieving the set of fields from any type
Reflection provides the GetFields() method for this purpose:
foreach (var field in myType.GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic))
// ...
I’m including the BindingFlags parameter here to ensure that it will include non-public fields, because otherwise it will return only public ones by default.
Setting the value of a field in any type
Reflection provides the function SetValue() for this purpose. You call this on a FieldInfo instance (which is returned from GetFields() above) and give it the instance in which you want to change the value of that field, and the value to set it to:
field.SetValue(myObject, myValue);
This is basically equivalent to myObject.Field = myValue;, except of course that the field is identified at runtime instead of compile-time.
Putting it all together
Here is a simple example. Notice you need to extend this further to work with more complex types such as arrays, for example.
public static T Deserialize<T>(XDataReader dataReader) where T : new()
{
return (T) deserialize(typeof(T), dataReader);
}
private static object deserialize(Type t, XDataReader dataReader)
{
// Handle the basic, built-in types
if (t == typeof(string))
return dataReader.ReadString();
// etc. for int and all the basic types
// Looks like the type t is not built-in, so assume it’s a class.
// Create an instance of the class
object result = Activator.CreateInstance(t);
// Iterate through the fields and recursively deserialize each
foreach (var field in t.GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic))
field.SetValue(result, deserialize(field.FieldType, dataReader));
return result;
}
Notice I had to make some assumptions about XDataReader, most notably that it can just read a string like that. I’m sure you’ll be able to change it so that it works with your particular reader class.
Once you’ve extended this to support all the types you need (including int? in your example class), you can deserialize an object by calling:
Foo myFoo = Deserialize<Foo>(myDataReader);
and you can do this even when Foo is a private type as it is in your example.

If I try to use sgen.exe (the standalone XML serialization assembly compiler), I get the following error message:
Warning: Ignoring 'TestApp.Program'.
- TestApp.Program is inaccessible due to its protection level. Only public types can be processed.
Warning: Ignoring 'TestApp.Program+Foo'.
- TestApp.Program+Foo is inaccessible due to its protection level. Only public types can be processed.
Assembly 'c:\...\TestApp\bin\debug\TestApp.exe' does not contain any types that can be serialized using XmlSerializer.
Calling new XmlSerializer(typeof(Foo)) in your example code results in:
System.InvalidOperationException: TestApp.Program+Foo is inaccessible due to its protection level. Only public types can be processed.
So what gave you the idea that XmlSerializer can handle this?
However, remember that at runtime, there are no such restrictions. Trusted code using reflection is free to ignore access modifiers. This is what .NET binary serialization is doing.
For example, if you generate IL code at runtime using DynamicMethod, then you can pass skipVisibility = true to avoid any checks for visibility of fields/classes.

I've been working a bit on this. I'm not sure if it will help but, anyway I think it could be the way. Recently I worked with Serialization and DeSerealization of a class I had to send over the network. As there were two different programs (the client and the server), at first I implemented the class in both sources and then used serialization. It failed as the .Net told me it had not the same ID (I'm not sure but it was some sort of assembly id).
Well, after googling a bit I found that it was because the serialized class was on different assemblies, so the solution was to put that class in a independent library and then compile both client and server with that library. I've used the same idea with your code, so I put both Foo class and FieldReader class in a independent library, let's say:
namespace FooLibrary
{
public class Foo
{
public string Field1 = null;
public int? Field2 = null;
}
public abstract class FieldReader<T>
{
public abstract void Fill(T entity, IDataReader reader);
}
}
compile it and add it to the other source (using FooLibrary;)
this is the code I've used. It's not exactly the same as yours, as I don't have the code for GetCSharpName (I used t.Name instead) and XDataReader, so I used IDataReader (just for the compiler to accept the code and compile it) and also change EntityField for object
public class ReflectionHelper
{
public static FieldReader<T> GetFieldReader<T>()
{
Type t = typeof(T);
string className = t.Name;
string readerClassName = Regex.Replace(className, #"\W+", "_") + "_FieldReader";
object[] fields = new object[10];
string source = GetFieldReaderCode(t.Namespace, className, readerClassName, fields);
CompilerParameters prms = new CompilerParameters();
prms.GenerateInMemory = true;
prms.ReferencedAssemblies.Add("System.Data.dll");
prms.ReferencedAssemblies.Add(Assembly.GetExecutingAssembly().GetModules(false)[0].FullyQualifiedName);
prms.ReferencedAssemblies.Add(t.Module.FullyQualifiedName);
prms.ReferencedAssemblies.Add("FooLibrary1.dll");
CompilerResults compiled = new CSharpCodeProvider().CompileAssemblyFromSource(prms, new string[] { source });
if (compiled.Errors.Count > 0)
{
StringWriter w = new StringWriter();
w.WriteLine("Error(s) compiling {0}:", readerClassName);
foreach (CompilerError e in compiled.Errors)
w.WriteLine("{0}: {1}", e.Line, e.ErrorText);
w.WriteLine();
w.WriteLine("Generated code:");
w.WriteLine(source);
throw new Exception(w.GetStringBuilder().ToString());
}
return (FieldReader<T>)compiled.CompiledAssembly.CreateInstance(readerClassName);
}
private static string GetFieldReaderCode(string ns, string className, string readerClassName, IEnumerable<object> fields)
{
StringWriter w = new StringWriter();
// write out field setters here
return #"
using System;
using System.Data;
namespace " + ns + ".Generated
{
public class " + readerClassName + #" : FieldReader<" + className + #">
{
public override void Fill(" + className + #" e, IDataReader reader)
" + w.GetStringBuilder().ToString() +
}
}";
}
}
by the way, I found a tiny mistake, you should use new or override with the Fill method, as it is abstract.
Well, I must admit that GetFieldReader returns null, but at least the compiler compiles it.
Hope that this will help you or at least it guides you to the good answer
regards

c# create an instance of an object from string

I have a string variable contain:
string classCode = "public class Person { public string Name{get;set;} }";
How can I create an instance of an object from the classCode ?
like
object obj = CreateAnInstanceAnObject(classCode);

You'll need to use CodeDom to compile an in-memory assembly, and then use reflection to create the type.
Here's a sample article on MSDN that walks through the process of code generation.
Once you've compiled the code, you can use Activator.CreateInstance to create an instance of it.

Building on the answers from above, here is a working demo to generate, compile and instantiate a class from an in-memory assembly:
namespace DynamicCompilation
{
using System;
using System.CodeDom;
using System.CodeDom.Compiler;
using System.Reflection;
using Microsoft.CSharp;
internal static class Program
{
private static void Main()
{
var ccu = new CodeCompileUnit();
var cns = new CodeNamespace("Aesop.Demo");
cns.Imports.Add(new CodeNamespaceImport("System"));
var ctd = new CodeTypeDeclaration("Test")
{
TypeAttributes = TypeAttributes.Public
};
var ctre = new CodeTypeReferenceExpression("Console");
var cmie = new CodeMethodInvokeExpression(ctre, "WriteLine", new CodePrimitiveExpression("Hello World!"));
var cmm = new CodeMemberMethod
{
Name = "Hello",
Attributes = MemberAttributes.Public
};
cmm.Statements.Add(cmie);
ctd.Members.Add(cmm);
cns.Types.Add(ctd);
ccu.Namespaces.Add(cns);
var provider = new CSharpCodeProvider();
var parameters = new CompilerParameters
{
CompilerOptions = "/target:library /optimize",
GenerateExecutable = false,
GenerateInMemory = true
};
////parameters.ReferencedAssemblies.Add("System.dll");
var results = provider.CompileAssemblyFromDom(parameters, ccu);
if (results.Errors.Count == 0)
{
var t = results.CompiledAssembly.GetType("Aesop.Demo.Test");
var inst = results.CompiledAssembly.CreateInstance("Aesop.Demo.Test");
t.InvokeMember("Hello", BindingFlags.Public | BindingFlags.Instance | BindingFlags.InvokeMethod, null, inst, null);
}
Console.ReadLine();
}
}
}

Simple put you cannot do this in one line as you are attempting. It is possible to create an instance of an existing class via it's name and one of the overloads of Activator.CreateInstance.
What you are trying to achieve here though is quite different. You are attempting to both 1) define a new class type and 2) create an instance of it. Defining new metadata in the running process dynamically is very difficult to achieve with static languages like C#. It requires a significant amount of work that can't easily be put into a StackOverflow answer.

The following project should guide you in what your trying to accomplish:
RunTime Code Compilation
However, if you are attempting to write code at runtime, you may want to rethink your architecture. You may be creating more of a headache for yourself than you need to be.
What are you trying to accomplish by creating this object?