I can't reference ImageSearch.dll in my project. I've been trying for days and can't get any further. it seems to me that i'm the only one with this problem and i don't know what to do next. Is it possible to reference a .dll manually, for example via lines of code? It's nerve wracking and need this or a similar feature.
I keep getting the following error:
Could not add a reference to imagesearch.dll. Make sure the file is accessible and is a valid assembly or COM component.
enter image description here
Hope someone can help me...
That message is telling you that the dll you're trying to reference is something that .NET doesn't know how to work with automatically. This means it has no idea what functions are in the dll or how they work. So, if a dll isn't a .NET assembly or exposed via COM, then you can use PInvoke (Platform Invoke).
Don't add the dll as a reference to your project at all, instead add it as a content file that gets output with the rest of your compiled code. Getting PInvoke to work with an arbitrary DLL can be quite complicated, so be prepared for some headaches. There's an entire website with examples of how to pinvoke for all sorts of libraries at http://pinvoke.net/ that will give you lots of ideas.
Then you can call methods in the dll by doing something like:
// Import ImageSearch.dll (containing the function we need) and define
// the method corresponding to the native function.
[DllImport("ImageSearch.dll"]
private static extern int FindImage(string imagePath);
Obviously I have no idea what imagesearch.dll is or does, so I have no idea what the actual PInvoke function should look like, you'll have to figure that out from the dll's interface.
https://learn.microsoft.com/en-us/dotnet/standard/native-interop/pinvoke
Related
I have a situation where I have a C# Managed DLL that is handling incoming real time data. The DLL filters and saves up to 200 of the most recent data points in a FIFO. I also have a C# application that on occasion needs to get some of the data from the DLL. I can easily setup methods in the DLL to return single values of the built in data types.
What I need is a way to pass a reference to my user defined type (EX: List ) to the DLL and have it fill it in. I cannot seem to find any way to tell the DLL about my types and the compiler complains that I do not know what I am doing. This is true. I have tried everything I can find on the internet.
Further my application already has a reference to the DLL so that it can start it up and respond to events, therefor I cannot add a reference to my application within the DLL without creating a circular reference.
So how can I inform my managed DLL about my managed application types? The end goal is to be able to pass an ObservableCollection and have the DLL fill in MyObject with data from its local cache of data points.
When searching the internet it seems that the managed to unmanaged scenario outweighs the managed to managed scenario by 98 plus percent.
Any ideas would be greatly appreciated.
To compile my comment as an answer:
You should have (naming is just ilustrative):
DataContract.dll with the definition of your types.
BusinessLogic.dll with the logic.
And Application.exe with your presentation logic.
DataContract.dll can then be referenced by both - BusinessLogic.dll and Application.exe.
I'm trying to use the SPARK particle system in OpenTK.
my project contains the header files in folders, with just two header files which only includes the others, and the folders contain the source files too.
I have tried several approaches so far, but nothing has worked for me yet, those are what I've tried:
1. P/Invoke
This is writing some code in your C++ project which built the dll and then using the DllImport attribute in C# (which obviously needs using System.Runtime.InteropServices;). I discovered the hard way that this doesn't work with classes, it only works for methods outside classes, so this approach was ineffective.
2. Wrapper classes
This is writing a class that contains a pointer to the original class. I discovered that the difficulty actually arises from calling unmanaged code(no automatic memory management) from managed code, that's why wrapper classes are needed, and that's why you have to redefine methods' signatures and let them call the original methods.
Of course this has advantages, like naming the classes and methods in a better way, but the library is so big so you can see the effort of this.
3. Use of an automatic wrapper:
This is a good approach, especially with xInterop++. I was really optimistic about this and thought it would work, it says "give me the .h files and the dll and I'll build the .NET dll for you". Good but doing so gives an error; in brief:
You must make sure .h files and the dll are consistent and that the
library works in a C++ project.
I have tried several things to deal with this error:
Knowing what the dll contains: it is difficult as I learned from Googling and from this site, so my try failed.
Putting header files in a new project and building it: received errors, fixed them, and then built the project and it worked well. I uploaded the dll file with the header files to xInterop. It then told the classes that were found but would then state that nothing was found! I searched and learned that the compiler must be told which classes are needed to be exposed by the dll by marking every class that is needed using the following statement:_declspec(dllexport).
I used Find & Replace to fix this thing and tried again and classes were shown, so I launched xInterop and received the same error.
It asked to ensure that the dll works. After verifying that the file worked I launched the program and linker errors were produced.
Here is where I'm stuck, these are the linker errors I get:
main.obj : error LNK2019: unresolved external symbol "void __cdecl
SPK::swapParticles(class SPK::Particle &,class SPK::Particle &)"
(?swapParticles#SPK##YAXAAVParticle#1#0#Z) referenced in function
"private: void __thiscall SPK::Pool::swapElements(class SPK::Particle &,class SPK::Particle
&)" (?swapElements#?$Pool#VParticle#SPK###SPK##AAEXAAVParticle#2#0#Z)
main.obj : error LNK2001: unresolved external symbol "unsigned int
SPK::randomSeed" (?randomSeed#SPK##3IA) main.obj : error LNK2001:
unresolved external symbol "unsigned long const SPK::NO_ID"
(?NO_ID#SPK##3KB) main.obj : error LNK2001: unresolved external symbol
"public: static float const * const SPK::Transformable::IDENTITY"
(?IDENTITY#Transformable#SPK##2QBMB)
This is the code that produced those errors:
#include "Extensions/Emitters/SPK_RandomEmitter.h"
using namespace SPK;
int main()
{
RandomEmitter e;
e.changeFlow(6);
e.getFlow();
return 0;
}
So that's my problem, I'm sorry for explaining too much but I've done a three days search without finding any solution.
PS:
the library is very big, so an automatic solution is a must.
This is a very, very unfriendly C++ library to have to interop with. Scratch the idea that pinvoke can work, C++ classes require C++/CLI wrappers. There are a great many classes with many small methods. The library depends on composition to generate effects so any approach that tries to do the interop with a few God classes is a dead avenue.
The most significant hazard is that it heavily relies on multiple inheritance. Not supported in .NET, this will defeat any tool that auto-generate wrappers. Also note that it only supports OpenGL rendering, not a terribly popular graphics api on Windows.
The library is attractive, and has been around for quite a while, but nobody has successfully ported it to .NET yet. This is unsurprising. In my opinion, you don't stand a chance. Only a rewrite could work.
PInvoke is the way to do what you are looking for. Doesn't matter if you have or do't have the code for that DLL so long you know the function signature.
Have a look at these articles from MSDN and code project that cover basics of PInvoke:
Platform Invoke Tutorial
P/Invoke Tutorial: Basics (Part 1)
Edit:
There are tools that can possibly generate DllImport signature for you. I have NOT tried any of these myself. Have a look:
P/Invoke Signature Generator
Easiest way to generate P/Invoke code?
This one
http://www.swig.org/
Hope that helps.
If your native dll exports some classes, then I would strongly suggest creating another native DLL wrapper for the original one. It should export a few functions and no classes at all.
Exported functioned could be something like:
my_lib_create_context( void ** const ppContext );
my_lib_delete_context( void * const pContext );
my_lib_do_something( void * const pContext, T param1, T param2 );
Inside my_lib_create_context() create an instance of your class and pass the pointer back through the ppContext parameter.
Inside my_lib_do_something() cast the pContext to a pointer of your class type and use it.
Also, when writing your wrapper, pay attention to calling convention, because you will need to pass that information to the .NET world (I think stdcall is default if not explicitly defined).
EDIT:
Regarding that part on how to do it:
Create a new C++ solution/project, select DLL type. Then add .def file to that project. Add to that file this:
EXPORTS
my_lib_create_context #1
my_lib_delete_context #2
my_lib_do_something #3
Then add some header file where you will put function signatures like this:
typedef void * SomeContext;
extern "C"
{
int __stdcall my_lib_create_context( /* [ out ] */ SomeContext * ppContext );
int __stdcall my_lib_delete_context( /* [ in ] */ SomeContext pContext );
// TO DO: ... you get it by now...
}
Implement these functions in .cpp file. Once you are done, create a wrapper in C# for this DLL and use it.
Hmm P/Invoke call GetProcessAdress .. so importing ABI problem is so so..
http://www.codeproject.com/Articles/18032/How-to-Marshal-a-C-Class
here are your answer give credit to those guy
Update 1:
I am wondering whether I can reference to a .lib file, but it seems that I cannot.
If this is true, and I have no source code of the C++ project, How can I use its methods?
Btw, I'm using FastCV library.
I come across a situation that I need to call C++ methods from C# code.
The C++ generated files structure:
lib
--libfastcv.lib
--vc120.pdb inc
--fastcv.h
--fastcv.inl
--stdint.h
I know how to call C++ methods from C# :
[DllImport("libfastcv.lib",CallingConvention=CallingConvention.Cdecl)]
public static extern <ReturnType> <MethodName>(<Parameters>);
But I think the .h and .inl files need to be included in my C# project as well.
So how to include them?
Thank you very much.
They don't. Instead, you need to build/use binary-compatible types in your own code, and use them. (And, you importing a method from dll, not from lib).
You dont have to do any includes. The DLLImport should be enough.
To see the Methods you can import you can use DependencyWalker or my favourite Tool CFF Explorer
I often used any WINAPI functions where i need some constants defined in headers. I always had to define them in my C# code too, theres no way to "import" them.
I am trying to make a program which will need to execute a lengthy algorithm over and over again, so C++seemed like the obvious choice to me. However, in order to make it look aesthetically pleasing, and to make its other functions easier to make, I built it in C# and made the algorithm in C++.
As far as I am aware, the best way for me to use the C++ function in my C# program is to PInvoke it. However, when I try to PInvoke the function from the DLL, I get an error saying
"Unable to find an entry point named <name> in DLL"
When I made my DLL, I used Visual C++ and created a Win32 Console application, selected DLL from the choices, and created the function in the test.cpp file. What did I do wrong?
You need to export the function in the native DLL.
I am not sure the best way to explain this so please leave comments if you do not understand.
Basically, I have a few libraries for various tasks to work with different programs - notification is just one example.
Now, I am building a new program, and I want it to be as lightweight as possible. Whilst I would like to include my notification engine, I do not think many people would actually use its functionality, so, I would rather not include it by default - just as an optional download.
How would I program this?
With unmanaged Dlls and P/Invoke, I can basically wrap the whole lot in a try/catch loop, but I am not sure about the managed version.
So far, the best way I can think of is to check if the DLL file exists upon startup then set a field bool or similar, and every time I would like a notification to be fired, I could do an if/check the bool and fire...
I have seen from the debug window that DLL files are only loaded as they are needed. The program would obviously compile as all components will be visible to the project, but would it run on the end users machine without the DLL?
More importantly, is there a better way of doing this?
I would ideally like to have nothing about notifications in my application and somehow have it so that if the DLL file is downloaded, it adds this functionality externally. It really is not the end of the world to have a few extra bytes calling notification("blabla"); (or similar), but I am thinking a lot further down the line when I have much bigger intentions and just want to know best practices for this sort of thing.
I do not think many people would
actually use its functionality, so, I
would rather not include it by default
- just as an optional download.
Such things are typically described as plugins (or add-ons, or extensions).
Since .NET 4, the standard way to do that is with the Managed Exensibility Framework. It is included in the framework as the System.ComponentModel.Composition assembly and namespace. To get started, it is best to read the MSDN article and the MEF programming guide.
You can use System.Reflection.Assembly and its LoadFile method to dynamically load a DLL. You can then use the methods in Assembly to get Classes, types etc. embedded in the DLL and call them.
If you just check if the .dll exists or load every .dll in a plugin directory you can get what you want.
To your question if the program will run on the user's machine without the dlls already being present - yes , the program would run. As long as you dont do something that needs the runtime to load the classes defined in the dll , it does not matter if the dll is missing from the machine. To the aspect you are looking for regarding loading the dll on demand , I think you are well of using some sort of a configuration and Reflection ( either directly or by some IoC strategy. )
Try to load the plugin at startup.
Instead of checking a boolean all over the place, you can create a delegate field for the notification and initialize it to a no-op function. If loading the plugin succeeds, assign the delegate to the plugin implementation. Then everywhere the event occurs can just call the delegate, without worrying about the fact that the plugin might or might not be available.