android 에서 NDK로 구조체 보내기

java

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package woenho.ns;



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);

        CTest test = new CTest();

        // Example of a call to a native method
        TextView tv = findViewById(R.id.sample_text);
        tv.setText(stringFromHello(test,"Example", 777));

    }

    /**
     * A native method that is implemented by the 'native-lib' native library,
     * which is packaged with this application.
     */
    public native String stringFromHello(CTest test,String strTitle, int nLuck);



    public class CTest{
        public CTest(){

            serial = 99;
            strData = "test data";
        }
        public long serial;
        public String strData ;
    }

}

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NDK

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extern "C" JNIEXPORT jstring JNICALL
Java_woenho_ns_MainActivity_stringFromHello(
        JNIEnv *env, jobject instance,
        jobject test, jstring strTitle, jint nLuck ) {

    jclass jClass;
    jClass = env->GetObjectClass(test);

    jfieldID fid;
    fid = env->GetFieldID(jClass, "serial", "J");

    jlong serial = 0;
    if( fid != NULL )
        serial = env->GetLongField(test, fid);

    char szMsg[512] = {0,};
    fid = env->GetFieldID(jClass, "strData", "Ljava/lang/String;");
    if( fid != NULL ) {
        jstring jstr = (jstring) env->GetObjectField(test, fid);
        if (jstr != NULL) {
            const char *pcName = env->GetStringUTFChars(jstr, NULL);
            strcpy(szMsg, pcName);
            // ReleaseStringUTFChars 반드시 해준다.
            env->ReleaseStringUTFChars(jstr, pcName);
        }
    }

    char hello[512]={0,};
    char title[512]={0,};

    const char *szParam = env->GetStringUTFChars(strTitle, NULL);
    strcpy( title, szParam);
    env->ReleaseStringUTFChars(strTitle, szParam);

    sprintf( hello, "%s(%lld:%s) -> %d", title, serial, szMsg, nLuck);

    return env->NewStringUTF(hello);
}

======================

Java VM Type Signatures

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TYPE SIGNATURE JAVA TYPE

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Z -> boolean

B -> byte

C -> char

S -> short

I -> int

J -> long

F -> float

D -> double

L fully-qualified-class ; -> fully-qualified-class --> string이 대표적

[ type -> type[]

( arg-types ) ret-type         -> method type

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For example, the Java method:

---------------------------------------------

long f (int n, String s, int[] arr); ->(ILjava/lang/String;[I)J   ====> ( "I", "Ljava/lang/String;", "[I", ) "J"

============

ref

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LPackage/StructType;