使用Android studio导入opencv几个sample示例代码

  • calibration
  • colorblob
  • facedection

其中facedection用到jni，环境配置需要配置ndk，以及编写cmakelist文件。

简单导入

  1. 下载opencv sdk

    下载 opencv 的 Android sdk，并解压到电脑某个路径

  2. 模块导入opencv sdk

    参考 opencv 开发环境搭建 将sdk/java中的代码通过 file-new-Import Module导入。

  3. 添加项目依赖

    在 file-Project Structure中选择应用模块，在dependencies 标签下添加dependence，选择刚才导入的opencv模块openCVLibrary341

  4. 添加jniLibs

    如果此时项目不加jniLibs，项目可以编译，但是运行时，回先提示安装open cv manager。就是要另外安装 sdk 目录中apk文件夹下对应的apk，例如 OpenCV_3.4.1_manager_arm64-v8a.apk。

    如果不想要另外安装的，则需要将 sdk-native-libs下的 so 文件复制导入项目的jniLibs中。

    这样编译之后的apk比较大，要好几十M。

    如果是简单的使用opencv 的sdk，例如sample中的color bob示例，这这里的配置就可以了，以下是涉及到ndk编程，项目需要编写cpp文件然后再参与编译，例如示例代码中的facedetection。

涉及jni

  1. 下载ndk

    File-Project structure - sdk Location。 查看Android NDK location，如果为空，点击底部的Download 即可自动下载，并配置好nkd的位置，如 …../sdk/android-sdk-macosx/ndk-bundle

    还需要下载cmake：Android studio打开preference对话框，查找 android sdk，在sdk tools标签下勾选下载 cmake。

  2. c/c++源码文件夹

    在main目录下创建cpp文件夹，用于存放cpp文件。

  3. 编写CMakeLists.txt

    cmake文件可以参考在Android studio中新建一个c++ support项目而自动生成的cmakelist文件。参考如下：

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    cmake_minimum_required(VERSION 3.4.1)

    #include open cv sdk中的jni include路径，不然
    include_directories(/Users/zowee-laisc/lynn/opencv/OpenCV-android-sdk/sdk/native/jni/include)

    #导入项目jniLibs文件夹下载 so库
    add_library( # Sets the name of the library.
                 lib_opencv

                 # Sets the library as a shared library.
                 SHARED

                 IMPORTED)

    set_target_properties(lib_opencv
                          PROPERTIES IMPORTED_LOCATION
                          ${CMAKE_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libopencv_java3.so)

    #编译添加自己的jni 库
    add_library( # Sets the name of the library.
                 detection_based_tracker

                 # Sets the library as a shared library.
                 SHARED

                 # Provides a relative path to your source file(s).
                 src/main/cpp/DetectionBasedTracker_jni.cpp )

    # Searches for a specified prebuilt library and stores the path as a
    # variable. Because CMake includes system libraries in the search path by
    # default, you only need to specify the name of the public NDK library
    # you want to add. CMake verifies that the library exists before
    # completing its build.

    find_library( # Sets the name of the path variable.
                  log-lib

                  # Specifies the name of the NDK library that
                  # you want CMake to locate.
                  log )

    # Specifies libraries CMake should link to your target library. You
    # can link multiple libraries, such as libraries you define in this
    # build script, prebuilt third-party libraries, or system libraries.

    target_link_libraries( # Specifies the target library.
                           detection_based_tracker

                           lib_opencv

                           # Links the target library to the log library
                           # included in the NDK.
                           ${log-lib} )

  1. 修改gradle文件

    修改应用gradle文件，主要是

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    externalNativeBuild {
               cmake {
                   cppFlags "-frtti -fexceptions"
                   abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'
                   arguments "-DANDROID_STL=gnustl_static"
               }
           }

    完整文件如下：

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apply plugin: 'com.android.application'

android {
    compileSdkVersion 27



    defaultConfig {
        applicationId "com.zowee.facedection"
        minSdkVersion 21
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
                abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'
                arguments "-DANDROID_STL=gnustl_static"
            }
        }
    }

    sourceSets {
        main {
            jniLibs.srcDirs = ['src/main/jniLibs']
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }

    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }

}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:27.1.1'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    implementation project(':openCVLibrary341')
}

  1. 注意事项

    构建项目的时候，遇到的主要报错信息和解决方案

    • 用<>来导入文件出错，该用双引号导入

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      Error:(1, 10) error: 'DetectionBasedTracker_jni.h' file not found with <angled> include; use "quotes" instead

  • 无法找到 opencv2/core.hpp

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    Error:(2, 10) fatal error: 'opencv2/core.hpp' file not found
    Error:(2, 10) fatal error: 'opencv2/core.hpp' file not found

    在cmakelist文件中添加

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    include_directories(/Users/zowee-laisc/lynn/opencv/OpenCV-android-sdk/sdk/native/jni/include)

  • Linker命令错误

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    /Measurebox2/facedection/src/main/cpp/DetectionBasedTracker_jni.cpp
    Error:(36) undefined reference to `cv::CascadeClassifier::detectMultiSc
    Error:error: linker command failed with exit code 1 (use -v to see invocation)

    或者
    Error:(36) undefined reference to `cv::CascadeClassi

    解决方案

    检查gradle文件

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    cmake {
        cppFlags "-frtti -fexceptions"
        abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'
        arguments "-DANDROID_STL=gnustl_static"
    }

  • 删除部分libs文件夹

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    Error:Execution failed for task ':facedection:transformNativeLibsWithStripDebugSymbolForDebug'.
    > A problem occurred starting process 'command '/Users/zowee-laisc/lynn/sdk/android-sdk-macosx/ndk-bundle/toolchains/mips64el-linux-android-4.9/prebuilt/darwin-x86_64/bin/mips64el-linux-android-strip''

    解决方法将jniLibs下的mips64的so 库文件夹删除