JNI应用-初步应用

喜欢ヅ旅行 2023-02-17 05:19 72阅读 0赞

今天拉了一下3年前的ndk代码，发现和现在Android Studio生成的代码相差比较大，就重新写一个吧.

后面仍然会进一步探索，这个demo只是简单的融合生成的cpp文件和自建的cpp文件，在不同的路径下可以使用同一个库名称。

本章是否生成头文件不重要，可以应用即可。

因为本身比较简单，所以就不写注释了，如果有网友没接触过，可以留言提问。

# 创建项目 #

选择 Native C++

# 配置 #

## 创建对应的java文件 ##

MyJNI.java

package com.jiataoyuan.createsodemo;
    
    /**
     * created by Taoyuan on 2020/6/12
     */
    public class MyJNI {
        
        static {
        
            System.loadLibrary("myJNI");
        }
    
        public native String sayHello(String context);
        public native int sum(int x, int y);
    
    }

## main下的cpp文件夹中创建cpp文件 ##

MyJNI.cpp

//
    // Created by Taoyuan on 2020/6/12.
    //
    
    #include <jni.h>
    #include <string>
    #include "MyJNI.h"
    
    extern "C"
    JNIEXPORT jstring JNICALL
    Java_com_jiataoyuan_createsodemo_MyJNI_sayHello(JNIEnv *env, jobject instance, jstring content) {
        
        jboolean isCopy;
        const char *temp = env->GetStringUTFChars(content, &isCopy);
        std::string say = "say Hello!\n";
        say.append(temp);
        env->ReleaseStringUTFChars(content, temp);
        return env->NewStringUTF(say.c_str());
    }
    
    extern "C" //表示对java输出
    JNIEXPORT jint JNICALL
    Java_com_jiataoyuan_createsodemo_MyJNI_sum(JNIEnv *env, jobject instance, jint x, jint y) {
        
        return x + y;
    }

## 配置到CMakeLists.txt文件中 ##

MyJNI.java

# For more information about using CMake with Android Studio, read the
    # documentation: https://d.android.com/studio/projects/add-native-code.html
    
    # Sets the minimum version of CMake required to build the native library.
    
    cmake_minimum_required(VERSION 3.4.1)
    
    # Creates and names a library, sets it as either STATIC
    # or SHARED, and provides the relative paths to its source code.
    # You can define multiple libraries, and CMake builds them for you.
    # Gradle automatically packages shared libraries with your APK.
    
    add_library( # Sets the name of the library.
            myJNI
    
            # Sets the library as a shared library.
            SHARED
    
            # Provides a relative path to your source file(s).
            native-lib.cpp
            MyJNI.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.
            myJNI
    
            # Links the target library to the log library
            # included in the NDK.
            ${log-lib})

# 应用 #

在 MainActivity 中创建对象直接使用即可。

package com.jiataoyuan.createsodemo;
    
    import android.os.Bundle;
    import android.widget.TextView;
    import androidx.appcompat.app.AppCompatActivity;
    
    public class MainActivity extends AppCompatActivity {
        
    
        // Used to load the 'native-lib' library on application startup.
        static {
        
            System.loadLibrary("myJNI");
        }
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
        
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            // Example of a call to a native method
            TextView tv = findViewById(R.id.sample_text);
    
            MyJNI myJNI = new MyJNI();
            StringBuilder sb = new StringBuilder();
            sb
                    .append(stringFromJNI())
                    .append("\n")
                    .append(myJNI.sayHello("this is myJNI"))
                    .append("\n")
                    .append(myJNI.sum(10, 20))
                    .append("\n");
            tv.setText(sb);
        }
    
        /**
         * A native method that is implemented by the 'native-lib' native library,
         * which is packaged with this application.
         */
        public native String stringFromJNI();
    
    }

# 生成so文件 #

1.  build 或 make project
2.  找到目录 build -> intermediates -> cmake -> release或debug -> obj
3.  复制到 main 目录下的 jniLibs 目录中即可

如果使用so文件报错：`More than one file was found with OS independent path 'lib/armeabi-v7a/libmyJNI.so'`，请参考：

[https://blog.csdn.net/lftaoyuan/article/details/106718096][https_blog.csdn.net_lftaoyuan_article_details_106718096]

# 使用so文件 #

1.  删掉 MyJNI.cpp 文件
2.  在 CMakeLists.txt 文件中删掉 MyJNI.cpp
3.  在 native-lib.cpp 文件中添加 MyJNI.h 头文件
4.  运行即可，效果等同直接使用cpp文件

[https_blog.csdn.net_lftaoyuan_article_details_106718096]: https://blog.csdn.net/lftaoyuan/article/details/106718096