I'm trying to use OpenCv 4 on Xamarin.Android by Java Binding Template. These are the steps that i've done:
0) I've compiled opencv binaries through cmake and mingw64 to get .jar and .a
I've put the .jar and the static libraries (.a) in Jars forlder of Xamarin Java Binding Template and i've compiled the template.
1.a) .jar Build Action is EmbeddedJar
1.b) libs Build Action is EmbeddedNativeLibrary
I've added a reference to that template in my Xamarin.Android project: the opencv methods were recognized correctly!
But, when i try to execute:
Mat Source = Imgcodecs.Imread(ImagePath, Imgcodecs.ImreadGrayscale);
i get an error:
Java.Lang.UnsatisfiedLinkError: 'No implementation found for long org.opencv.imgcodecs.Imgcodecs.imread_0(java.lang.String, int) (tried Java_org_opencv_imgcodecs_Imgcodecs_imread_10 and Java_org_opencv_imgcodecs_Imgcodecs_imread_10__Ljava_lang_String_2I)'
I think that there could be a missmatch of method name, maybe due to a wrong java parsing.
I've also tried to use shared libries (.so) by loading them through JavaSystem.LoadLibrary("LibraryNameWithoutInitialLib"), but i have the same error :/
Do you know why?
You cannot link static libraries with Xamarin.Android as the Xamarin/Mono NDK-based runtime is a static main entry executable and does not dynamically get built per project. If you do not need to use a .jar/.aar high-level wrapper, then you will need to use runtime shared libraries and define DllImportAttribute entries for the exported functions that you need to call.
Xamarin.Android supports the use of native libraries via the standard PInvoke mechanism.
Using Native Libraries
Use C/C++ libraries with Xamarin
Note: There are numerous OpenCV C# wrappers / DllImport files in open source ( i.e. a github search away 😁)
Note: If you are using a 3rd-party .jar/.aar , make sure that they are using OpenCV shared libraries and thus not requiring a gradle script to link them into an NDK-based Android app.
Related
I am sorry maybe this is stupid what I am asking, but I have a question about linking static/shared libraries in android.
I am creating a new C++ Native android studio project. After build, I open the apk file, and inside lib the folder there are placed libraries libnative-lib.so for every ABI. Size of APK is 3.580 KB.
But if I change inside CMakeLists.txt to build the native lib like Static lib, so now I got this:
add_library(native-lib
STATIC
native-lib.cpp)
When APK is built, I can not find the static library (libnative-lib.a). There is no lib folder in the apk. Also, the size is 2.836 KB.
Can someone please explain(or give me link for more info about this) where is the library placed in the STATIC build?
And on run I got error if I link static:
No implementation found for java.lang.String com.example.myapplication.MainActivity.stringFromJNI()
You can't use native static libraries directly in Android apps.
Android user space is basically a Java (or more precisely Dalvik VM).
So all user-facing applications must be written in Java or Kotlin (which both compile to Dalvik bytecode).
Static C/C++ libraries must be link in to a C/C++ executable or dynamic library to be used. They can not be loaded directly by Linux or Android.
Since Android app does not have a C/C++ executable in it, the only way to use a static library with an Android app is to link it with a dynamic library (*.so) that can be loaded via Java Native Interface.
Since JNI uses the system loader to load the library, it can only load dynamic libraries, and of those, only ones that export functions with proper naming conventions so they can be matched to a Java class that will be used to call the native code.
I have a pre-built java library as a compile time dependency for Android library project(AAR). So while building it in Android Studio, 'compileOnly' is used so that the same gets linked in runtime when deployed with an APK.
However, I should also write an equivalent Android.mk for the library project. I am not able to find any reference to include a prebuilt java library in Android.mk. Can someone help me on this part.
I tried using LOCAL_PREBUILT_JAVA_LIBRARIES attribute, but the system threw an error:
error: dont use LOCAL_PREBUILT_JAVA_LIBRARIES anymore LOCAL_PATH=xxx.
This kind of dependency linking may look strange. Let me give some insight into it also. Basically I am building an application that has one small part being developed by a third party. The setter interface APIs for the third party are shipped in by me in the form of a .jar file so that they use the same as a compile time dependency and build an AAR out of it.
Now the third party project is to be included in my project build(AOSP). This brings a dependency that their module should be compiled for the AAR to get generated and my project uses that AAR to generate the APK.
For the AAR to get compiled and built, I need to link the prebuilt java interface library that is shipped in by me(mentioned in the first step).
Need an equivalent of 'compileOnly' used in build.gradle.
I'm trying to integrate this specific library to my Android project, and the library is written in C/C++. I've miraculously gotten ndk-build to give me the needed .so file.
However, looking at it, there's a sample in the project, and they use a mysterious .jar with the API bindings of the .c/c++ files.
How do i either
create this special .jar file that has the API, based on the .so?
OR
directly add a method to the main c++ file and then call it from Java?
I've tried to re-wrap things using JNI, but it definitely doesn't seem to work. i keep getting UnsatisfiedLinkError.
A lot of the documentation online uses jni as the tutorial. i'm happy with just a few links to tutorials on JNA.
JNA provides a stub native library, libjnidispatch.so for a variety of platforms. You can build this library yourself, or extract one of the pre-built binaries from the project's lib/native/<platform>.jar packages.
You include libjnidispatch.so in your Android project the way you would any other JNI library. This is required; you cannot rely on JNA to dynamically unpack and use its native library automatically like on other platforms. The JNA project includes details for doing so (as well as instructions for building libjnidispatch.so yourself).
You then use jna.jar as you would any other Java jar file, and write your own (Java) mappings to match the native library you're trying to access. There's also a jna-min.jar which omits all the native platform libraries that are normally bundled in jna.jar.
Do go to project properties and build paths and remove JNA 4.0 and related classes.
This will work!
What I would like to do is to add C++ Library (.a) file into my C++ / Java Hybrid Project.
Actually, It's Android Project. I'm using C++ for native calls.
The problem is I can't find any "Tool Settings" under "C++ Build/
Settings" to add ".a" library file into the project.
I think it is because of the nature or type of the Project. (As my project is Android Project.) Any points would be much obliged.
I have .h file and .a file. I can include ".h" file. But, when I invoke the method, the compiler said "no such method".
I would like to add C++ Library (.a) file into Android Project. ( C++ / Java Hybrid Project.)
PS: I know Eclipse is poor in C++ Code Analysis. I have already turn off the Code Analysis in the project. So, It's obvious that the error is not C++ Code Analysis.
Check this link should help.
http://www.cmumobileapps.com/2011/08/31/compiling-open-source-libraries-with-android-ndk-part-1/
This explains how to compile c/c++ source to produce static library, and then use this static library.
Hello i'm using JNA to be able to use an external .dll(i don't have the header file but i have documentation thus the exposed function signatures).
I have managed to use my dll in a java project following the instructions here and now i'm trying to use the same thing on an android app.
I imporetd the jna jar in my libs and also added the jar in my buildpath and i'm getting an error
The library 'jna-3.5.1.jar' contains native libraries that will not run on the device.
The following libraries were found:
com/sun/jna/linux-amd64/libjnidispatch.so
com/sun/jna/darwin/libjnidispatch.jnilib
com/sun/jna/linux-i386/libjnidispatch.so
com/sun/jna/sunos-x86/libjnidispatch.so
com/sun/jna/sunos-amd64/libjnidispatch.so
com/sun/jna/sunos-sparc/libjnidispatch.so
com/sun/jna/sunos-sparcv9/libjnidispatch.so
Any ideas?
This deserves an answer...
Did you compile the lib you wanna use for android?
Why not write a JNI wrapper around those native libs, and invoke that from your android app?
Browse your jna.jar and delete the files displayed on your message :
com/sun/jna/linux-amd64/libjnidispatch.so
com/sun/jna/darwin/libjnidispatch.jnilib
com/sun/jna/linux-i386/libjnidispatch.so
com/sun/jna/sunos-x86/libjnidispatch.so
com/sun/jna/sunos-amd64/libjnidispatch.so
com/sun/jna/sunos-sparc/libjnidispatch.so
com/sun/jna/sunos-sparcv9/libjnidispatch.so
Then maybe you need to restart your IDE and that should work.