android studio ndk 开发

新建工程, 选中Include C++ Support

一路Next之后, 在最后Finish页面尽量选中图示两项, 这样会给我们包裹一些特定的示例代码, 帮助我们理解和使用

自动生成的代码:

MainActivity.java

public class MainActivity extends AppCompatActivity {

    // Used to load the 'native-lib' library on application startup.
    static {
        System.loadLibrary("native-lib");
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Example of a call to a native method
        TextView tv = (TextView) findViewById(R.id.sample_text);
        tv.setText(stringFromJNI());
    }


    public native String stringFromJNI();

}

CMakeLists.txt

# 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).

             src/main/cpp/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} )

app/main/src/native-lib.cpp

#include <jni.h>
#include <string>

extern "C"
JNIEXPORT jstring JNICALL
Java_thereisnospon_ndkdemo_MainActivity_stringFromJNI(
        JNIEnv *env,
        jobject /* this */) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

自己模仿写个 lib : c1

Hello.java

public class Hello {

    static {
        System.loadLibrary("c1");
    }

    public static native String getStr();
}

app/main/src/c1.cpp

#include<jni.h>
#include<string>


using namespace std;
extern "C"  // 记得加这个。。
JNIEXPORT jstring JNICALL
Java_thereisnospon_ndkdemo_Hello_getStr(JNIEnv *env, jclass type) {

    // TODO

    string c="ldsf";
    return env->NewStringUTF(c.c_str());
}

CMakelists.txt 添加

add_library(
             c1

             SHARED

             src/main/cpp/c1.cpp)