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JNI初级demo

JNI初级demo

作者: Android刘东 | 来源:发表于2020-05-26 14:53 被阅读0次

    ndk引入

    0.配置:

    androidstudio :
    preferences->Android SDK->SDK Tools 下载NDK +CMake
    
    1590475246611.jpg

    1.新项目:

    androidstudio :
    file->new project->natite c++(下滑才能看见)
    

    2.local.properties

    这里查看是否有ndk.dir=/../..
    如未有,则添加ndk.dir=/Users/admin/Library/Android/sdk/ndk/../
    

    3.cpp位于main目录下,和java同级

    新项目自动创建,老项目创建CMakeLists.txt
    创建个xx.cpp
    

    4.MainActivity.java来个方法测试

    package main;
    
    import android.app.Activity;
    import android.app.ActivityManager;
    import android.content.Context;
    import android.os.Bundle;
    import android.widget.TextView;
    
    import androidx.annotation.Nullable;
    import androidx.appcompat.app.AppCompatActivity;
    
    import com.zhisheng.test.R;
    
    import java.util.List;
    
    public class MainActivity extends Activity {
        static {
            System.loadLibrary("native-lib");
        }
    
        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.inflate);
            (((TextView)(findViewById(R.id.tvTwoJump)))).setText(getStringJNI());
        }
    
        public native String getStringJNI();
    }
    
    

    4.cpp来个方法测试

    #include <jni.h>
    #include <string>
    
    
    extern "C"
    JNIEXPORT jstring JNICALL
    //方法名:Java_包名_类名_java调用方法名
    //个人理解 c++很少了解
    Java_main_MainActivity_getStringJNI(JNIEnv *env, jobject thiz) {
        // TODO: implement getStringJNI()
        std::string hello = "Hello2222 from C++";
        return env->NewStringUTF(hello.c_str());
    }
    

    项目测试完成

    CMakeLists.txt 上传一下哈

    # 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.
                 native-lib
    
                 # Sets the library as a shared library.
                 SHARED
    
                 # Provides a relative path to your source file(s).
                 native-lib.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.
                           native-lib
    
                           # Links the target library to the log library
                           # included in the NDK.
                           ${log-lib} )
    

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