OpenCV - undefined reference to 'cv::CascadeClassifier::detectMultiScale() after NDK update

Question

Yesterday I updated my Android Studio included NDK to version 17.0.4754217and since then I can\'t run my app anymore. When I tried to rerun the code after the u

Answer 1

I solved this problem by using mix with this OpenCV + contrib lib (opencv4_1_0_contrib) and official Java OpenCV classes (4.3). Successfully run official OpenCV FaceDetection example on Android 9.

---

Some usefull code:

App level build.gradle:

android{defaultConfig{
//...
externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
                abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'
                //I import OpenCV as module and provide it path to CMake
                arguments "-DOpenCV_DIR=/" + rootProject.projectDir.path + "/sdk/native"
             }
        }
}}

externalNativeBuild {
        cmake {
            path "src/main/cpp/CMakeLists.txt"
            version "3.10.2"
        }
    }

My CMakeLists.txt:

# Sets the minimum version of CMake required to build the native library.
cmake_minimum_required(VERSION 3.4.1)

#Add OpenCV 4 lib
include_directories(${OpenCV_DIR}/jni/include) #Path from gradle to OpenCV Cmake
add_library( lib_opencv SHARED IMPORTED )
set_target_properties(lib_opencv PROPERTIES IMPORTED_LOCATION ${OpenCV_DIR}/libs/${ANDROID_ABI}/libopencv_java4.so)

#Add Your Native Lib
add_library(native-lib SHARED native-lib.cpp)
add_library(detection_based_tracker SHARED detectionbasedtracker_jni.cpp)

#Add&Link Android Native Log lib with others libs
find_library(log-lib log)
target_link_libraries(detection_based_tracker lib_opencv ${log-lib})

---

NDK version was 21.0.611669. Also I don't use arguments for CMake like -DANDROID_STL=gnustl_static.