这是我的解决方案。

特征

1. 适用于Android和iOS。
2. 使用静态链接而不是动态链接。（因此，代码大小要小得多。）
3. 最新版本为2020.07.28。（由于这些API的变化很快，而且许多文章都有些陈旧。）

入门

注意：如果您已经有一个应用程序，则可以跳过本节：)本节假定您根本没有任何代码。

可以从此处下载示例代码。

步骤0 ：确保您具有Flutter环境，并遵循官方的“使用Flutter编写C
++”教程。

注意 ： 必须 遵循“在iOS上，您需要告诉Xcode静态链接文件：…”的步骤。否则，在我们的最后一步，iOS将抱怨找不到该符号。

第1步
：使用OpenCV编写所需的任何代码。例如，我更改ios/Classes/native_add.cpp为以下愚蠢的代码，与官方教程中的代码几乎相同：

#include <stdint.h>
#include <opencv2/core.hpp>

extern "C" __attribute__((visibility("default"))) __attribute__((used))
int32_t native_add(int32_t x, int32_t y) {
    cv::Mat m = cv::Mat::zeros(x, y, CV_8UC3);
    return m.rows + m.cols;
}

安卓系统

步骤0
：从官方网站下载Android OpenCV sdk
。假设我将其放在桌面上。/Users/tom/Others/OpenCVRelease/OpenCV- android-sdk

步骤1.1 ：将更android/CMakeLists.txt改为以下内容。 注意
：首先将更OPENCV_BASE_DIR改为您的文件夹。

cmake_minimum_required(VERSION 3.4.1)

# TODO please change me!
set(OPENCV_BASE_DIR "TODO PLEASE PUT YOUR DIR HERE!!!")

set(OPENCV_INCLUDE_DIR "${OPENCV_BASE_DIR}/sdk/native/jni/include/")
set(OPENCV_STATIC_LIB_DIR "${OPENCV_BASE_DIR}/sdk/native/staticlibs/${ANDROID_ABI}")
set(OPENCV_3RDPARTY_STATIC_LIB_DIR "${OPENCV_BASE_DIR}/sdk/native/3rdparty/libs/${ANDROID_ABI}")

include_directories(${OPENCV_INCLUDE_DIR})

find_library(log-lib log)

add_library(highgui STATIC IMPORTED)
set_target_properties(highgui PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_highgui.a)

add_library(calib3d STATIC IMPORTED)
set_target_properties(calib3d PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_calib3d.a)

add_library(core STATIC IMPORTED)
set_target_properties(core PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_core.a)

add_library(dnn STATIC IMPORTED)
set_target_properties(dnn PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_dnn.a)

add_library(flann STATIC IMPORTED)
set_target_properties(flann PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_flann.a)

add_library(imgproc STATIC IMPORTED)
set_target_properties(imgproc PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_imgproc.a)

add_library(videoio STATIC IMPORTED)
set_target_properties(videoio PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_videoio.a)

add_library(imgcodecs STATIC IMPORTED)
set_target_properties(imgcodecs PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_imgcodecs.a)

add_library(features2d STATIC IMPORTED)
set_target_properties(features2d PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_features2d.a)

add_library(ml STATIC IMPORTED)
set_target_properties(ml PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_ml.a)

add_library(photo STATIC IMPORTED)
set_target_properties(photo PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_photo.a)

add_library(shape STATIC IMPORTED)
set_target_properties(shape PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_shape.a)

add_library(objdetect STATIC IMPORTED)
set_target_properties(objdetect PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_objdetect.a)

add_library(stitching STATIC IMPORTED)
set_target_properties(stitching PROPERTIES IMPORTED_LOCATION ${OPENCV_STATIC_LIB_DIR}/libopencv_stitching.a)

include(AndroidNdkModules)
android_ndk_import_module_cpufeatures()

set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
set(THREADS_PREFER_PTHREAD_FLAG TRUE)
find_package(Threads REQUIRED)

add_library(tbb STATIC IMPORTED)
set_target_properties(tbb PROPERTIES IMPORTED_LOCATION ${OPENCV_3RDPARTY_STATIC_LIB_DIR}/libtbb.a)

add_library(tegra_hal STATIC IMPORTED)
set_target_properties(tegra_hal PROPERTIES IMPORTED_LOCATION ${OPENCV_3RDPARTY_STATIC_LIB_DIR}/libtegra_hal.a)

add_library(ittnotify STATIC IMPORTED)
set_target_properties(ittnotify PROPERTIES IMPORTED_LOCATION ${OPENCV_3RDPARTY_STATIC_LIB_DIR}/libittnotify.a)

add_library(native_with_opencv

        # Sets the library as a shared library.
        SHARED

        # Provides a relative path to your source file(s).
        ../ios/Classes/native_add.cpp
        )

target_link_libraries(native_with_opencv
        ${log-lib}
        core
        # note: You can import whatever other modules you like (e.g. dnn)
        tbb # note: need to be placed *after* "core"
        cpufeatures
        ittnotify
        tegra_hal # NOTE if still have error, check abiFilters, since tegra does *not* exist in x86.
        Threads::Threads
        -lz
        )

当然，lib/native_with_opencv.dart应该将.so文件名更改为"libnative_with_opencv.so"。

步骤1.2 ：更改android/build.gradle以下内容：

android {
    ...
    defaultConfig {
        ...
        // [[[CHANGE 1: Make minSdkVersion bigger]]]
        // see https://github.com/opencv/opencv/issues/14419
        minSdkVersion 21

        // [[[CHANGE 2: Add these flags and filters]]]
        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions -std=c++11"
                abiFilters 'armeabi-v7a', 'arm64-v8a'
            }
        }
        ...
    }
    ...
}

当然，minSdkVersion实际项目（native_with_opencv/example/android/app/build.gradle）中的也应更改为21。

完成！编译并享受它（并转到iOS的下一部分）！如果看到1 + 2 == 3，则一切正常。

奖励：如果您在发布模式下构建并查看apk大小，您将看到我们的.so文件小于1MB。因此，静态链接和减小文件大小确实有效:)

的iOS

步骤0 ：在中ios/native_with_opencv.podspec，添加：

  s.static_framework = true
  s.dependency 'OpenCV', '~> 4.1'

步骤1 ：编译并享受。 注意： 您可能需要先运行pod install下native_with_opencv/example/ios让Cocoapod初始化。

（可选）Android配置如何工作的说明：（1）最初，我只是链接core，但是有数百个链接错误。然后，我搜索并修复每个组。例如，error: undefined reference to 'carotene_o4t::...'意味着我需要与链接libtegra_hal，因此我添加了几行。（2）奇怪的是，tbb应该放在 之后
core，否则它仍然不会链接。（3）abiFilters是必需的，因为tegra_hal不支持x86（因此不.a存在文件）。（4）minSdkVersion需要复活，否则fegetenv将找不到。