Develop Reference

can .net windows forms project and .net UWP project be merged?

I have a GUI windows form app written in .NET .
And I have a new .NET UWP app that has UWP camera and UWP sockets.
Can I port the UWP camera and UWP sockets code into the .NET Windows form app project?
(If I went the other way, it probably will take much longer to port the Windows forms GUI into a UWP GUI.)

WinForm project can use most new Windows 10 API designed for UWP. Check this post.
If went the other way, you need to port bit by bit of the existing GUI, so it all depends how complex your WinForm GUI is.
The first challenge is you are using XAML, another language instead of C# to write UWP UI.
Some WinForm controls you are using just do not have a UWP counterpart, you need to turn to the community to check if there are alternatives that are freely available l, or purchase proprietary product, or write your own control.

No. WinForm and UWP projects are very different. UWP are compiled to native code and WinForm are compiled to IL that are then run by the CLR. Microsoft is currently working on the ability to put a UWP control inside a WinForm application. You can check it out here.

Is it possible to Convert or wrap C# APP to IO Xcode Apple APP and Android

I have an app developed for windows 10 on C# and now I want to move to IOS and Android. I have heard of xamarin and used some of there stuff in C# but would it be possible to embed the C# code and move it to apple xcode without having to redevelop the app from again?

would it be possible to embed the C# code and move it to apple xcode without having to redevelop the app from again?
No, it is not possible. Basically you can share some UIs across different platforms, but I think redevelop your app for each platform is necessary.
Not sure if you want to use Xamarin.Android and Xamarin.iOS or Xamarin.Forms to develop your app, you can use C# for development by using Xamarin, it provides a cross-platform implementation of the extensive features in .Net framework, but the actual implementation on each system is very different. For more information, you can refer to Understanding the Xamarin Mobile Platform.
For Xamarin.Android and Xamarin.iOS, you can refer to Android Architecture and iOS Architecture.
For Xamarin.Forms, you can have your UIs and some basic features designed in the PCL in order to share across different platforms, but for most features just for example like working with files, we need to access the native method of each platform, therefor, Xamarin.Forms provides a locator named DependencyService to achieve this.

background task and SQLite in windows Universal 8.1

I created a project of Windows Universal app. Then I add a new Runtime Component (background task C#) for update my tile.
Then I install sqlite-net for background task. I want to read some data from my database.
When I want to run my app, I get some error from SQLite.cs.
http://borjianamin.persiangig.com/errors.png
I search a little and I found this Topic: (I'm sorry for this because I don't have enough reputation)
stackoverflow.com/questions/14812076/how-to-connect-to-sqlite-database-from-windows-runtime-component-which-is-for-ru
github.com/praeclarum/sqlite-net/issues/104
I use replace tool of VS2015 and replace all public with internal But I get about 300 errors this time.
This is my background task project only:
Link: http://www.rodfile.com/uu9viaaxsz91
Is it possible to help me?
Thanks.

Yes it is possible. You have to add a separate project for SQLite called Class Library.
Then you have to add sqlite.net in that class library. After that you need to add the reference of Class Library on Windows Runtime Component.

How can I port my Windows Phone game to a Silverlight thing that I can use on a webpage?

I'm confused about how to port my WP7 C# game to the web using Silverlight.
I know that code written in C# using the Windows Phone (add-in? plugin? other?) for Visual Studio makes a Silverlight app. But how can I embed my finished WP7 app in a webpage?
I've seen some things such as ExEn, SilverSprite, and XnaTouch {the page redirects to MonoGame}, but I'm confused if I even need something like this in order to make my game playable on the web. I've got a feeling the capability may even be embedded in Visual Studio. Is it even possible to do this without rewriting all the code?
Shortened version: How can I port my WP7 C# game to the web using Silverlight?

Create a new project in Visual Studio targeting Silverlight beside your WP7 project. Then if your existing code is structured nicely, you should be able to re-use most of your "back-end" code (the views, viewmodels people talk of). The best way to do this for files that are common is to add them as links to the new project, so you don't have to keep them both up to date - if there are small changes between versions you can use conditional compilation to do this.
You'll want to use some completely new classes for some things, such as probably the top level view. Some XAML (eg a UserControl definition) might be usable between both with changes, though some people will favour always creating different versions. Have a look at this extensive article on cross-platform SL/WPF/WP7 development.

What have you tried?
If you create a Silverlight application in Visual Studio, you should be able to include all your existing Views, ViewModels, resources and so on. I don't know if you'll be able to make a single project that both builds into a WP7 and a Silverlight application but I personally wouldn't bother trying.

You can't directly - there are missing runtime components and features that are only available to Windows Phone applications.
You can, however, reuse lots of code, especially C# - all XAML code, I beleive, you'll have to copy/paste from WP7 XAML to Silverlight XAML.

An embedded application for windows desktop using .NET platform?

I'm rebuilding an Embedded application:
Prebuild application Specifications:
Use : For dispaying the captured images/video from microscope image capturing device on windows based PC or Laptops.
Sepcifications: Prebuild on .NET plateform using VC++
Flaws : Lacks some specified features.
Current Requirement:
Want to rebuild that entire application using C# and add some additional client features.
My Questions:
Is it feasible to develop such application in C#.net?
If yeh,What kind of resources available in C# to develop desktop embedded application?
Any references which show any of such kind of application?
Your suggestions on building this kind of application.
P.S. It is essential to buid it on .NET platform.

I think by "Prebuild" you mean "Existing". Why do you want to rewrite the complete application? As you have stated that the application is written in C++.Net. You can easily add all the new functions in C# and use that code from your existing C++.Net code.

Note: I'm making this answer CW because the question is hard on the limit towards some close reasons. Everyone feel free to edit and extend it.
Is it feasible to develop such application in C#.net?
That's a tough one...from the top of my head I'd argue that it doesn't matter. If you know C#, then build it in C#, if the client wants it in C#, then build it in C#. You'll most likely have to use COM-Components or API-Invokes anyway to accomplish this.
If it is a TWAIN device, you might be better of to stick with VC++, I found TWAIN on .NET a real pain in the a** and have given up on such features. Same goes for WIA, but that might just be me.
If yes, what kind of resources available in C# to develop desktop embedded application?
I guess you mean a Widget? In that case I have no idea, I never really looked at that (at least not on Windows). But as far as I know widgets on Windows consist of a data-backend and a HTML/JavaScript-Frontend, so you'll most likely have to develop the two separately.
Any references which show any of such kind of application?
I guess any WIA/TWAIN application would be a reference, at least your description sounds so.
Your suggestions on building this kind of application.
See your first question.