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Converting a C# class I created inside a project to a separate reusable class

I'm not new to C# programming, but I suppose I'm new to programing "the right way" in C#. I've worked in C on embedded devices for years and have written desktop apps to support them. First in VB6, then in C#.
I recently started making better use of classes for reusing code (and for instantiating more than one instance of the class in a program). For example, I "wrapped" a UART interface with some additional functionality so I can use the same code for multiple ports by creating an instance of the class for each one.
It is in a separate file, but still in the same program namespace, so when I want to reuse it, I have to copy the file and change the namespace to the new project.
I'm sure there's a way to create it such that I can just reference it like everything else with either a "using..." reference at the top of the program or with a "Project | References..." checkbox. But for the life of me I can't find a good learning journey for this.
Any direction would help.

You want to create your reuseable class in an assembly - this is the equivalent of a dll from your C experience.
To create an assembly, have a separate project of type assembly (instead of exe) . You can reference the assembly from other projects. If your project is in the same solution you can reference the project, otherwise you can reference the compiled assembly.
C# uses a packaging system called Nuget, so you can package your assemblies into "Nugets" which you host in a Nuget Server. You can then use tooling to discover and import these.

Please create a Class Library project and include your class into that project. Make sure your class is public. Once you build this project you'll get an assembly which can be referenced from other projects. See Tutorial: Create a .NET class library using Visual Studio
There are different ways of referencing it.
You can have the class library project in the same solution as the main project. In this case you should add a project reference.
You can copy the compiled *.dll file to some folder in your solution (e.g. Lib) and add an assembly reference.
If this assembly is to be used in multiple projects please consider creating a NuGet package with this library and pushing it to some repository. Then other projects can add a package reference to this package.
Details:
How to: Add or remove references by using the Reference Manager
Install and manage packages in Visual Studio using the NuGet Package Manager

It is in a separate file, but still in the same program namespace, so when I want to reuse it, I have to copy the file and change the namespace to the new project.
Well, it isn't the best practice but (unfortunatly) still a common behavior. So don't worry to much about it.
What you could do to improve it place the file (and other reusable parts) in a seperated csproj.
For example name the project of the type class library and name it VinDag.Tools. Within the project create a folder UART and place the wrapper there. The namespace of the wrapper would then be VinDag.Tools.UART.
From know on you can just reference the class library instead of renaming the file. It's not necessarily required to be the same namespace as the project.
From there you can start considering (private) nugets. This would prevent you from copying files/csproj around.

Using third party controls

I am pretty new to WPF Developing and i am trying work with the GraphSharp lib within my project but I cant access the GraphSharp.Controls dll classes.
i declared this row in my mainwindows.xaml file
xmlns:gsc = "clr-namespace:GraphSharp.Controls;assembly=GraphSharp.Controls"
and when I try to write
<gsc:GraphLayout/>
Note-GraphLayout is a class that represents a graph in xaml
I tried to look on how to declare namespace in xaml and other resources but couldn't find a good answer for my problem...

Did you try to rebuild the solution after adding the GraphSharp lib? In order for the XAML designer/editor to see it, it needs to have the solution rebuilt. Otherwise it will give you an error stating it could not be found.
I just added the GraphSharp lib to a project and was able to use the same namespace you provided, so the namespace is valid.
Also make sure you have added a reference to the GraphSharp library in your project. The best way to do this is via NuGet. Right-Click on your project References and chose to add a new NuGet package. Search for GraphSharp and install it.

Referencing a Windows Phone Runtime Component DLL/WinMD from another project

I need to implement a wrapper to expose some native C++ code to C#, and have followed this tutorial:
http://www.silverlightshow.net/items/Windows-Phone-8-Native-Code-Support.aspx
So far in my C# test project, I don't have problems instantiating a class written in C++/CX from the Runtime Component project and using methods from that class, so long as I reference the entire project (.sln).
Visual Studio doesn't allow me to reference the Runtime Component DLL alone, but does allow me to reference the .winmd file in the project. C# then recognizes the namespace correctly, however at runtime I get a TypeLoadException when trying to create the same object.
This doesn't appear to be a namespace problem (as mentioned here: Changing namespace name of C++ component in Windows Phone causes exception), since everything is alright so long as I create a project reference (or does referencing a project vs a .winmd affect the namespace somehow?).
Is it possible to bundle the Runtime Component in some form that an end user can reference it without needing to provide the entire project?

You need to add following the to WMAppManifest.xml
<ActivatableClasses>
<InProcessServer>
<Path>YourComponent.dll</Path>
<ActivatableClass ThreadingModel="both" ActivatableClassId="YourComponentNamespace.YourComponent"/>
</InProcessServer>
</ActivatableClasses>
With YourComponent being the name of your WinMD.

I think what you are seeing is a manifestation of the problem described here.
In short, when creating a WinRT component using C++, just referencing the output DLL or the output winmd is not sufficient. You need both.

I had this same problem, and (eventually) figured out that the .dll and .winmd file needed to have the same name (which was the same as the namespace they defined) and be in the same directory.
For example, if your classes are in the X::Y namespace, the files must be X.Y.dll and X.Y.winmd.
Then all I needed to do was add a reference to the .winmd file in my project (by right-clicking on the References folder for that project in the Solution Explorer, choosing "Add Reference...", then choosing "Browse" from the dialog that comes up). I didn't need to add anything to the manifest file.

Create a component for the palette

I have never created a component before, but now have a few which are basically .cs files. They are of type System.Windows.Forms.Control.
But they are only available on the control palette when I am using the solution they are part of. It makes use of a few images which are in the /Resources folder.
Is there a way to make the component into a DLL, so that I can use it in any project by simply referencing it? Or else, make it into a component that always appears in my palette?

You need to create a Control Library project, which is a Class Library (DLL) that contains public classes that inherit Control.
You can then add a reference to the compiled DLL (or to the project if it's in the same solution) and the controls will appear in your toolbox.

Read resources from a DLL file

I've two Visual Basic 2008 projects - one is a class library project and another is a Windows Forms project. In the class library project, I've defined some strings in the project resources (project properties > Resources tab).
I build that class library project and get the DLL file from the debug folder and added up as a reference in my Windows Forms project.
How do I read those strings from the referenced DLL file?

While you can dynamically load the DLL as ho suggests, it's fine to use a reference as you have done. In fact I would recommend using a reference unless you had a particular requirement to dynamically load the resource assembly.
As to accessing the resources there are a few things you need to do.
In the resource assembly you will need to ensure the resources are public. By default resources are set to internal which means you will not see the resources in the winforms app. Double click on Properties\Resources.resx to open the resources view. In the top toolbar you will see a label "Access Modifier" next to a combo box drop down. Change the selection to public.
You will need to reference the assembly from the forms app. You have stated you have already done this. Just a note that a better way to do this is to create a solution that contains both projects. Then in the forms app choose add reference. Click on the Projects tab up the top. Double click on the resource DLL project name. This works better than referencing the debug DLL directly since it means if you change between a release build and debug build in your forms app, it will automatically build a matching release/debug version of your resource assembly.
Once you have added the reference you can simply reference the type out of the resources DLL, e.g.
ResourceDLLNamespace.Properties.Resource.ResourceName
Just a note, you need to be aware of type name clashes if you are using the same namespace for your forms app and resource DLL. In this situation both your forms app will have access to it's own Properties.Resources class as well as that of the resource DLL. You can do two things to avoid this:
Use a different namespace between the two assemblies
In the resource assembly don't include a default Properties\Resources.resx resource dictionary. Delete it and manually add a new resource, i.e. Add New Item and select "Resources File". You should find that you will not be able to add the new resource dictionary to the Properties folder - add it to the root or some other folder as you require. This will automatically give it a different type name by virtue of being in a different folder. You still may want to avoid using the resource file name of "Resources" however, as if you have all the relevant namespaces in scope via using statements you will get the same issue that the compiler won't know which version of Resources to use.
-Donovan

I think you just use System.Reflection.Assembly.Load to load the other assembly then use the constructor of System.Resources.ResourceManager that takes an assembly.
Note, I don't think it needs to a reference for this to work.