Android Studio 配置 OpenCV4+

https://stackoverflow.com/questions/63382489/cant-import-opencv-module-in-android-studio

1. 新建Project，选择Native C++。

2. 下载并解压OpenCV Android SDK，如OpenCV4.5.0 Android SDK。

3. File/New/Import Module, 选择sdk文件夹（不是sdk/java文件夹！）

4. File -> Project Structure -> Dependencies -> Module Dependency -> add OpenCV as 'Module Dependency' of 'app'

5. Clean Project

6. 注意代码中需要OpenCVLoader。此时可在Java中使用OpenCV。

package com.example.testopencv;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

import org.opencv.android.OpenCVLoader;
import org.opencv.core.Mat;
import org.opencv.core.CvType;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "main_activity";
    // Used to load the 'native-lib' library on application startup.
    static {
        if (!OpenCVLoader.initDebug()) {
            // Handle initialization error
            Log.d(TAG, "OPENCV DİD NOT LOAD");
        }
        System.loadLibrary("native-lib");
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Mat mat = Mat.eye(3, 3, CvType.CV_8UC1);
        // Example of a call to a native method
        TextView tv = findViewById(R.id.sample_text);
        tv.setText(stringFromJNI());
    }

    /**
     * A native method that is implemented by the 'native-lib' native library,
     * which is packaged with this application.
     */
    public native String stringFromJNI();
}

 6. 在native code中使用opencv：

a. 修改CMakeLists.txt，添加内容：

find_package(OpenCV 4.5 REQUIRED java)
target_link_libraries(native-lib ${OpenCV_LIBRARIES})

b. 修改cmake相关选项(注意是在defaultConfig中的）：

defaultConfig {
        ...
        externalNativeBuild {
            cmake {
                cppFlags "-std=c++14 -frtti -fexceptions"
                arguments "-DOpenCV_DIR=" + "/mnt/ntfs_sdb2/linux_partition/android_projects/TestOpencv/sdk/native/jni" // , "-DANDROID_ARM_NEON=TRUE"
            }
        }

---

OpenCV 官方说明

//
// Notes about integration OpenCV into existed Android Studio application project are below (application 'app' module should exist).
//
// This file is located in <OpenCV-android-sdk>/sdk directory (near 'etc', 'java', 'native' subdirectories)
//
// Add module into Android Studio application project:
//
// - Android Studio way:
//   (will copy almost all OpenCV Android SDK into your project, ~200Mb)
//
//   Import module: Menu -> "File" -> "New" -> "Module" -> "Import Gradle project":
//   Source directory: select this "sdk" directory
//   Module name: ":opencv"
//
// - or attach library module from OpenCV Android SDK
//   (without copying into application project directory, allow to share the same module between projects)
//
//   Edit "settings.gradle" and add these lines:
//
//   def opencvsdk='<path_to_opencv_android_sdk_rootdir>'
//   // You can put declaration above into gradle.properties file instead (including file in HOME directory),
//   // but without 'def' and apostrophe symbols ('): opencvsdk=<path_to_opencv_android_sdk_rootdir>
//   include ':opencv'
//   project(':opencv').projectDir = new File(opencvsdk + '/sdk')
//
//
//
// Add dependency into application module:
//
// - Android Studio way:
//   "Open Module Settings" (F4) -> "Dependencies" tab
//
// - or add "project(':opencv')" dependency into app/build.gradle:
//
//   dependencies {
//       implementation fileTree(dir: 'libs', include: ['*.jar'])
//       ...
//       implementation project(':opencv')
//   }
//
//
//
// Load OpenCV native library before using:
//
// - avoid using of "OpenCVLoader.initAsync()" approach - it is deprecated
//   It may load library with different version (from OpenCV Android Manager, which is installed separatelly on device)
//
// - use "System.loadLibrary("opencv_java4")" or "OpenCVLoader.initDebug()"
//   TODO: Add accurate API to load OpenCV native library
//
//
//
// Native C++ support (necessary to use OpenCV in native code of application only):
//
// - Use find_package() in app/CMakeLists.txt:
//
//   find_package(OpenCV 3.4 REQUIRED java)
//   ...
//   target_link_libraries(native-lib ${OpenCV_LIBRARIES})
//
// - Add "OpenCV_DIR" and enable C++ exceptions/RTTI support via app/build.gradle
//   Documentation about CMake options: https://developer.android.com/ndk/guides/cmake.html
//
//   defaultConfig {
//       ...
//       externalNativeBuild {
//           cmake {
//               cppFlags "-std=c++11 -frtti -fexceptions"
//               arguments "-DOpenCV_DIR=" + opencvsdk + "/sdk/native/jni" // , "-DANDROID_ARM_NEON=TRUE"
//           }
//       }
//   }
//
// - (optional) Limit/filter ABIs to build ('android' scope of 'app/build.gradle'):
//   Useful information: https://developer.android.com/studio/build/gradle-tips.html (Configure separate APKs per ABI)
//
//   splits {
//       abi {
//           enable true
//           universalApk false
//           reset()
//           include 'armeabi-v7a' // , 'x86', 'x86_64', 'arm64-v8a'
//       }
//   }
//

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 https://www.cnblogs.com/imoon22/p/14902927.html