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Difference Between DLL Reference's? And Uses?

Please any one explain this. This Question helps to understand common things
Question:
What is the difference between when you 'add DLL reference from one project to another project via Browse Option and Add DLL reference from Solution project to another project and copy-paste from one project to another project'?
I have found an answer on google
Answer:
Adding a project reference adds a local project's DLL to the project that references it, and every time the solution compiles, the updated DLL for that project gets copied to the other project. So when you go through the build process, if you have 5 projects, each one rebuilds its DLL, and copies that DLL to its references.
But:
I don't know what the process is and the difference when we copy-paste from one project to another project?

When you do copy paste from One project to another, the dependent project add its reference of the file that you have paste in the project solution directory
When you do copy paste the dll of one project to the other project's directory and then Add its reference by browsing to that directory where you have pasted your dll. Then VS only add its reference and copy that dll to its bin folder and show you (allows you) all the method and properties that it contains.
If you do any change in your source project solution like adding or modifying methods then the updated dll of that project is not available in your dependent project solution.
So VS still points to the old dll file just because of the reference you added. So whenever you made any change in your source project solution, you have to add the reference of the updated dll to your dependent solution every time.
In Second Case: When you add reference of your source project into your dependent project solution, VS always take the most recent updated dll from your source project into your dependent project. So in this way you don't need to add reference every time you compile the code or debug.

When you just reference a DLL by browsing to it, VS would copy it to the output directory of the dependent project.
Suppose afterwards that DLL is updated - there is no guaranty that VS would retake that updated DLL, and copy it again to the output directory of the dependent project - which mean, that even after you fixed some bugs in the other project, those bug would persist in the dependent project (because it is still using the previous version of that DLL).
When you add reference to other project in the solution, VS would always take the most recent and updated DLL outputted from that project.

VisualStudio doesn't recognize a new reference that I add

I have written a DLL and then in my solution I am adding a reference to it, but when I declare it in the usings section, it gives me error that this is not recognized, are you missing a reference?
here is how I set up my solution...
1- First I had created my DLL. Let's name it MyDLLLibrary, sitting somewhere on hard drive.
2- I also had a solution, consisting of several other projects...for all of these I have created a folder like "C:\_debug" and I have set "Output Path" and "Reference Path" of all these projects to point to that common folder. So far, s good.
3- Now I add that MyDLLLibrary to this solution, change its "Output" and Reference Path to point to the same common debug folder, use Add Refrence and at the reference to MyDLLLibrary to the project I want in the solution and rebuild the solution...
Now if I use a using statement, still it doesn't recognize it.
I even tried the add refrence from projects tab..that didn't work either.

Check the project properties of both assemblies and make sure that the framework setting for both is .NET Framework 4 and not .NET 4.0 Client Profile or something else.

While using Visual Studio 2017, I had to close visual studio and delete the .vs folder (at the root of the solution). This fixed my issues

vs2010 - reference .exe not working

I've got a project (project A)in vs2010 (c#) that I want to reference another project (.exe) (project B) that I created. Project A is a quick, down & dirty util that I will only use once but I need all the function calls and db calls from project B, so rather than cut, copy, pasting from one to another, I thought I could just reference project B in my references. I am able to point to the .exe and in code i can use it, but when I compile it, it complains about not being able to see it (the infamous "are you missing a using directive or assembly reference?" error).
Does anyone know how I can do this?

Most probably, also it's hard to say, you have .NET Framework version conflict. One of your projects has .NET Framework version which is not compatible with other.
Check in project properties of both of them the version of the framework.
Make them the same
Recompile both of them
and most probably the trouble will gone.
Hope this helps.

Make sure the namespace of classes you want to use from project A is included in the files in your project B in a using directive:
using projA.ExampleNamespace;

I have the same problem. When I first added the reference all worked fine. But some time later after a rebuild there were errors and the classes and namespaces of "project A" were not longer recognized. Removing and re-adding the reference solved the problem immediately (without rebuiling or anything). There were no errors in other code and all DLLs and EXEs were build correctly. Build Order and Build Dependency settings were also correct. Seems to be a strange bug in Visual Studio (I use 2013 Professional).
I also checked how the reference was set in csproj file. The csproj file didn't change at all after removing and re-adding the reference. Neither did the sln file.
Maybe it's some strange caching behavior. But as I used "Rebuild All" which cleans up temporary files imho, this shouldn't happen. Even restarting VS or the PC didn't help.

Amazon Mechanical Turk DLL references keep disappearing during compilation

I've downloaded and compiled Amazon's .NET SDK for Mechanical Turk, producing two DLLs: Amazon.WebServices.MechanicalTurk.dll and Amazon.WebServices.MechanicalTurk.Domain.dll .
I then created a new WPF project and added the two DLLs as references. When I create objects from their space, Intellisense has no trouble browsing the assemblies- I can see the classes inside.
When I compile, however, I get an "type not found" error from the compiler. Intellisense no longer works for the Amazon namespace, and the DLLs have vanished from the Object Browser window inside Visual Studio, though they're still listed as references in Solution Explorer.
What's going on? I think I'm missing something obvious. I can see, for example, MTConfig, but when I try to instantiate it, it fails and I need to re-add the DLLs to try again.
Thanks!

How have you added the references? Did you copy the DLLs into your new project's output folder and add references to them there? I can imagine that giving the behaviour you describe, if VS wipes the output folder before a build. If that's what's happening, simply move the DLLs to a different directory (I typically create a "lib" directory) and point the reference there.

What I did to solve this same problem was to recompile the DLLs changing the .NET version from 2.0 to 4.0 in the project properties. Not sure why that works, but in my case it solved the issue.

C# dll not updating across projects

I've got a C# project in visual studio that is building a DLL, and another console project which includes the first as a reference. These are both in the same solution.
The trouble is when I add methods to the DLL, then rebuild the console project doesn't seem to pick them up.
For example, in the DLL I have a class Converters. If I add a method
public static void test() {}
it just doesnt' show up in the console app at all. Intellisense doesn't autocomplete it, and if I manually type it in it gives a compiler error.
If I go in and delete the dll files then rebuild that works (or better yet, delete the bin and obj directories) but that seems rather drastic.
I'm sure this is a basic error, but I can't seem to find the solution after some googling.

How are you adding the reference? As a project reference or by browsing to the DLL? If you're using the latter then it will copy it locally to the bin directory of your console app and won't refresh it unless you manually delete it. If you add it as a project reference it will copy it as and when it needs to.

The exact thing happened to me once on a project - it turned out the build command wasn't configured to build these DLLs.
Check Build - Configuration Manager, and make sure the project is checked:
(Image from msdb - Setting the Build Configuration)

close Project visualStudio and
rebuild again your dll (other project visualStudio)

One of the things to note is the Target Framework of the Projects, if you compile your Project A with target framework different then that of Project B and it is referencing the dlls of Project A you may run into this kind of trouble. So, make sure that the target framework for both Projects is same.

Check that you don't have the ddl inside the bin folder of your project. Whilst I was adding the reference by browsing for the dll, I had forgotten that I manually copy pasted a version into that folder. No matter how many times I cleaned and rebuilt, it didn't seem to update.
Deleting that dll and re-referencing fixed the issue.

Change the reference to the dll to the Project, instead of the output.

This is certainly unexpected behavior. It sounds like the reference between the two projects is broken in some way. Two issues come to mind.
Possible problem with the reference. Try deleting the reference in solution explorer and readding the reference and seeing if that fixes things. When you re-add make sure it's a project reference and not a file reference.
It's possible that the time stamps on the files in your project are off. See if they are in the future.

check the folder which contains the reference. does it contain a refresh file with a relative path in it? if so, and if assembly names in the location pointed to by the relative path are common with those in of (project) references which should auto update, then these references no longer auto update! what you end up is a static reference to the assemblies present in the relative path contained in the refresh file.
you may also have to delete the projectreferences key in the sln file and add references afresh

I hate to beat a dead SO question but 8 years after the original question and none of the above solving the issue for me, my problem was in VS2013, but to solve it I simply removed and re-added the reference to the DLL in the project that invokes it.
I hope this helps some people in the newer VS realm having the same issue.