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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

Swashbuckle parameter descriptions

I'm using SwaggerResponse attributes to decorate my api controller actions, this all works fine, however when I look at the generated documentation the description field for parameters is empty.
Is a there an attribute based approach to describe action parameters (rather than XML comments)?

With the latest Swashbuckle, or better said at least the Swashbuckle.AspNetCore variant which I'm using, the Description field for parameters can now be displayed correctly as output.
It does require the following conditions to be met:
XML comments must be enabled and configured with Swagger
Parameters should be explicitly decorated with either [FromRoute], [FromQuery], [FromBody] etc.
The same for the method type (get/post/put etc.), which should be decorated with [Http...]
Describe the parameter as usual with a <param ...> xml comment
A full sample looks like this:
/// <summary>
/// Short, descriptive title of the operation
/// </summary>
/// <remarks>
/// More elaborate description
/// </remarks>
/// <param name="id">Here is the description for ID.</param>
[ProducesResponseType(typeof(Bar), (int)HttpStatusCode.OK)]
[HttpGet, Route("{id}", Name = "GetFoo")]
public async Task<IActionResult> Foo([FromRoute] long id)
{
var response = new Bar();
return Ok(response);
}
Which produces the following output:

You should confirm you are allowing Swagger to use XML comments
httpConfig.EnableSwagger(c => {
if (GetXmlCommentsPath() != null) {
c.IncludeXmlComments(GetXmlCommentsPath());
}
...
...
);
protected static string GetXmlCommentsPath() {
var path = HostingEnvironment.MapPath("path to your xml doc file");
return path;
}
You should also check you are generating XML doc for your desired project. Under your desired project Properties (Alt + Enter on top of the project or Right Click -> Properties) -> Build -> Check XML documentation file

For completeness sake, when using latest version of Swashbuckle.AspNetCore (2.1.0) and Swashbuckle.SwaggerGen/Ui (6.0.0), enable Xml documentation file generation in your project's Build
Then the following to your ConfigureServices() method:
services.ConfigureSwaggerGen(options =>
{
options.SingleApiVersion(new Info
{
Version = "v1",
Title = "My API",
Description = "API Description"
});
options.DescribeAllEnumsAsStrings();
var xmlDocFile = Path.Combine(AppContext.BaseDirectory, $"{_hostingEnv.ApplicationName}.xml");
if (File.Exists(xmlDocFile))
{
var comments = new XPathDocument(xmlDocFile);
options.OperationFilter<XmlCommentsOperationFilter>(comments);
options.ModelFilter<XmlCommentsModelFilter>(comments);
}
});

MvvmCross ViewTypeResolver doesn't resolve Tag (fragment or custom type)

Actual situation is, that I added to the MvxViewTypeResolver class the "Fragment"-Case, so it does look like this:
#region Copyright
// <copyright file="MvxViewTypeResolver.cs" company="Cirrious">
// (c) Copyright Cirrious. http://www.cirrious.com
// This source is subject to the Microsoft Public License (Ms-PL)
// Please see license.txt on http://opensource.org/licenses/ms-pl.html
// All other rights reserved.
// </copyright>
//
// Project Lead - Stuart Lodge, Cirrious. http://www.cirrious.com
#endregion
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.Views;
using Cirrious.MvvmCross.Binding.Android.Interfaces.Binders;
namespace Cirrious.MvvmCross.Binding.Android.Binders
{
public class MvxViewTypeResolver : IMvxViewTypeResolver
{
private Dictionary<string, Type> _cache = new Dictionary<string, Type>();
public IDictionary<string, string> ViewNamespaceAbbreviations { get; set; }
#region IMvxViewTypeResolver Members
public virtual Type Resolve(string tagName)
{
Type toReturn;
if (_cache.TryGetValue(tagName, out toReturn))
return toReturn;
var unabbreviatedTagName = UnabbreviateTagName(tagName);
var longLowerCaseName = GetLookupName(unabbreviatedTagName);
var viewType = typeof(View);
#warning AppDomain.CurrentDomain.GetAssemblies is only the loaded assemblies - so we might miss controls if not already loaded
var query = from assembly in AppDomain.CurrentDomain.GetAssemblies()
from type in assembly.GetTypes()
where viewType.IsAssignableFrom(type)
where (type.FullName ?? "-").ToLowerInvariant() == longLowerCaseName
select type;
toReturn = query.FirstOrDefault();
_cache[tagName] = toReturn;
return toReturn;
}
private string UnabbreviateTagName(string tagName)
{
var filteredTagName = tagName;
if (ViewNamespaceAbbreviations != null)
{
var split = tagName.Split(new char[] {'.'}, 2, StringSplitOptions.RemoveEmptyEntries);
if (split.Length == 2)
{
var abbreviate = split[0];
string fullName;
if (ViewNamespaceAbbreviations.TryGetValue(abbreviate, out fullName))
{
filteredTagName = fullName + "." + split[1];
}
}
}
return filteredTagName;
}
#endregion
protected string GetLookupName(string tagName)
{
var nameBuilder = new StringBuilder();
switch (tagName)
{
case "View":
case "ViewGroup":
nameBuilder.Append("android.view.");
break;
case "fragment":
nameBuilder.Append("android.app.");
break;
default:
if (!IsFullyQualified(tagName))
nameBuilder.Append("android.widget.");
break;
}
nameBuilder.Append(tagName);
return nameBuilder.ToString().ToLowerInvariant();
}
private static bool IsFullyQualified(string tagName)
{
return tagName.Contains(".");
}
}
}
Now it is submitting the correct longLowerCaseTagName (android.app.fragment) but in the query it isn't able to resolve the type.
My suggestion is, that the fragment-control isn't loaded when the type should be resolved. Maybe there is an other way to get the type resolved?
Also if I add a custom type (giving the tag Mvx.MyCustomType in the axml) it doesn't get resolved. Do I have to add something in the MvxBindingAttributes.xml in this case?
Thanks for the help!

First an explanation of the code:
The custom XML inflater factory used by the MvvmCross Binder tries to load Views in a very similar way to the standard 2.x Android XML inflater.
The default code for the view type resolution is indeed in: https://github.com/slodge/MvvmCross/blob/master/Cirrious/Cirrious.MvvmCross.Binding/Android/Binders/MvxViewTypeResolver.cs
If your xml contains a name such as <MyCompany.MyProject.MyViews.MyFirstView /> then the view type resolver:
first checks for abbreviations and expands these into full namespaces - by default the only known abbreviation is Mvx. which is expanded to: Cirrious.MvvmCross.Binding.Android.Views.. If you want to add more abbrevations then override ViewNamespaceAbbreviations in https://github.com/slodge/MvvmCross/blob/master/Cirrious/Cirrious.MvvmCross.Binding/Android/MvxBaseAndroidBindingSetup.cs
then checks to see if the unabbreviated name is a non-namespaced name. If it is, then it assumes that the class is the Android namespace and prepends it with android.view. or android.widget.
then converts the fully namespaced name to all lowercase as a case-insensitive lookup key
uses that lowercase key to search all Types which derive from View in all loaded assemblies.
caches the result (whether its null or not) in order to speed up subsequent inflations.
All of this behaviour was designed to match the default Android xml view inflation code in http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/2.3.6_r1/android/view/LayoutInflater.java#LayoutInflater.createViewFromTag%28java.lang.String%2Candroid.util.AttributeSet%29
With that explanation out of the way - here's an answer to your questions:
MvvmCross does not yet currently contain any Fragment support. The official MonoDroid fragment support itself was only released last week, and I've not yet had anybody request fragments - Android "fragmentation" seems to have kept most people back on Activity and Dialog based code.
Briefly ;ooking at the documentation, fragment isn't an Android View - it looks like Fragment inherits directly from Java.Lang.Object - see http://developer.android.com/reference/android/app/Fragment.html
Because of this, there's no way that the MvvmCross ViewTypeResolver will currently work with fragments.
I would suggest that if you need both mvvmcross and fragments today, then your best bet is to replace the default resolver (using IoC) with your own resolver - but I can't offer much advice on this as I haven't yet fully read and understood the droid docs on http://developer.android.com/guide/topics/fundamentals/fragments.html
From my experience in creating the current inflation code, then I think you will find the source essential reading when you do this - e.g. see : http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.0.1_r1/android/view/LayoutInflater.java#LayoutInflater.createViewFromTag%28android.view.View%2Cjava.lang.String%2Candroid.util.AttributeSet%29
I can't give you any information on when official mvvmcross fragment support will be available - it's not something that is currently scheduled.
Custom views are supported, but will not normally live in the Mvx. abbreviated namespace.
They are much more likely to live in your UI application namespace, or in some shared library.
To see a custom view in action, see the PullToRefresh example in the tutorial - https://github.com/slodge/MvvmCross/blob/master/Sample%20-%20Tutorial/Tutorial/Tutorial.UI.Droid/Resources/Layout/Page_PullToRefreshView.axml

How do I programmatically get the GUID of an application in C# with .NET?

I need to access the assembly of my project in C#.
I can see the GUID in the 'Assembly Information' dialog in under project properties, and at the moment I have just copied it to a const in the code. The GUID will never change, so this is not that bad of a solution, but it would be nice to access it directly. Is there a way to do this?

Try the following code. The value you are looking for is stored on a GuidAttribute instance attached to the Assembly
using System.Runtime.InteropServices;
static void Main(string[] args)
{
var assembly = typeof(Program).Assembly;
var attribute = (GuidAttribute)assembly.GetCustomAttributes(typeof(GuidAttribute),true)[0];
var id = attribute.Value;
Console.WriteLine(id);
}

Or, just as easy:
string assyGuid = Assembly.GetExecutingAssembly().GetCustomAttribute<GuidAttribute>().Value.ToUpper();
It works for me...

Another way is to use Marshal.GetTypeLibGuidForAssembly.
According to MSDN:
When assemblies are exported to type libraries, the type library is assigned a LIBID. You can set the LIBID explicitly by applying the System.Runtime.InteropServices.GuidAttribute at the assembly level, or it can be generated automatically. The Tlbimp.exe (Type Library Importer) tool calculates a LIBID value based on the identity of the assembly. GetTypeLibGuid returns the LIBID that is associated with the GuidAttribute, if the attribute is applied. Otherwise, GetTypeLibGuidForAssembly returns the calculated value. Alternatively, you can use the GetTypeLibGuid method to extract the actual LIBID from an existing type library.

You should be able to read the GUID attribute of the assembly via reflection. This will get the GUID for the current assembly:
Assembly asm = Assembly.GetExecutingAssembly();
object[] attribs = asm.GetCustomAttributes(typeof(GuidAttribute), true);
var guidAttr = (GuidAttribute) attribs[0];
Console.WriteLine(guidAttr.Value);
You can replace the GuidAttribute with other attributes as well, if you want to read things like AssemblyTitle, AssemblyVersion, etc.
You can also load another assembly (Assembly.LoadFrom and all) instead of getting the current assembly - if you need to read these attributes of external assemblies (for example, when loading a plugin).

For an out-of-the-box working example, this is what I ended up using based on the previous answers.
using System.Reflection;
using System.Runtime.InteropServices;
label1.Text = "GUID: " + ((GuidAttribute)Attribute.GetCustomAttribute(Assembly.GetExecutingAssembly(), typeof(GuidAttribute), false)).Value.ToUpper();
Alternatively, this way allows you to use it from a static class:
/// <summary>
/// public GUID property for use in static class </summary>
/// <returns>
/// Returns the application GUID or "" if unable to get it. </returns>
static public string AssemblyGuid
{
get
{
object[] attributes = Assembly.GetEntryAssembly().GetCustomAttributes(typeof(GuidAttribute), false);
if (attributes.Length == 0) { return String.Empty; }
return ((System.Runtime.InteropServices.GuidAttribute)attributes[0]).Value.ToUpper();
}
}

There wasn't any luck here with the other answers, but I managed to work it out with this nice one-liner:
((GuidAttribute)(AppDomain.CurrentDomain.DomainManager.EntryAssembly).GetCustomAttributes(typeof(GuidAttribute), true)[0]).Value

To get the appID you could use the following line of code:
var applicationId = ((GuidAttribute)typeof(Program).Assembly.GetCustomAttributes(typeof(GuidAttribute), true)[0]).Value;
For this you need to include the System.Runtime.InteropServices;

Use:
string AssemblyID = Assembly.GetEntryAssembly().GetCustomAttribute<GuidAttribute>().Value;
Or in VB.NET:
Dim AssemblyID As String = Assembly.GetEntryAssembly.GetCustomAttribute(Of GuidAttribute).Value

How can I discover the "path" of an embedded resource?

I am storing a PNG as an embedded resource in an assembly. From within the same assembly I have some code like this:
Bitmap image = new Bitmap(typeof(MyClass), "Resources.file.png");
The file, named "file.png" is stored in the "Resources" folder (within Visual Studio), and is marked as an embedded resource.
The code fails with an exception saying:
Resource MyNamespace.Resources.file.png cannot be found in class MyNamespace.MyClass
I have identical code (in a different assembly, loading a different resource) which works. So I know the technique is sound. My problem is I end up spending a lot of time trying to figure out what the correct path is. If I could simply query (eg. in the debugger) the assembly to find the correct path, that would save me a load of headaches.

This will get you a string array of all the resources:
System.Reflection.Assembly.GetExecutingAssembly().GetManifestResourceNames();

I find myself forgetting how to do this every time as well so I just wrap the two one-liners that I need in a little class:
public class Utility
{
/// <summary>
/// Takes the full name of a resource and loads it in to a stream.
/// </summary>
/// <param name="resourceName">Assuming an embedded resource is a file
/// called info.png and is located in a folder called Resources, it
/// will be compiled in to the assembly with this fully qualified
/// name: Full.Assembly.Name.Resources.info.png. That is the string
/// that you should pass to this method.</param>
/// <returns></returns>
public static Stream GetEmbeddedResourceStream(string resourceName)
{
return Assembly.GetExecutingAssembly().GetManifestResourceStream(resourceName);
}
/// <summary>
/// Get the list of all emdedded resources in the assembly.
/// </summary>
/// <returns>An array of fully qualified resource names</returns>
public static string[] GetEmbeddedResourceNames()
{
return Assembly.GetExecutingAssembly().GetManifestResourceNames();
}
}

I'm guessing that your class is in a different namespace. The canonical way to solve this would be to use the resources class and a strongly typed resource:
ProjectNamespace.Properties.Resources.file
Use the IDE's resource manager to add resources.

I use the following method to grab embedded resources:
protected static Stream GetResourceStream(string resourcePath)
{
Assembly assembly = Assembly.GetExecutingAssembly();
List<string> resourceNames = new List<string>(assembly.GetManifestResourceNames());
resourcePath = resourcePath.Replace(#"/", ".");
resourcePath = resourceNames.FirstOrDefault(r => r.Contains(resourcePath));
if (resourcePath == null)
throw new FileNotFoundException("Resource not found");
return assembly.GetManifestResourceStream(resourcePath);
}
I then call this with the path in the project:
GetResourceStream(#"DirectoryPathInLibrary/Filename");

The name of the resource is the name space plus the "pseudo" name space of the path to the file. The "pseudo" name space is made by the sub folder structure using \ (backslashes) instead of . (dots).
public static Stream GetResourceFileStream(String nameSpace, String filePath)
{
String pseduoName = filePath.Replace('\\', '.');
Assembly assembly = Assembly.GetExecutingAssembly();
return assembly.GetManifestResourceStream(nameSpace + "." + pseduoName);
}
The following call:
GetResourceFileStream("my.namespace", "resources\\xml\\my.xml")
will return the stream of my.xml located in the folder-structure resources\xml in the name space: my.namespace.