Simple JNI

package com.maxwin.dab.jni;
public class Lib {
    public native void hello();
}

Java_com_maxwin_dab_jni_Lib_hello(JNIEnv* env, jobject thiz);

Rule

JAVA_ + package name + class name + func name

Add some args

public native void arg1(int a);
public native void arg2(int a, int b);

void Java_com_maxwin_dab_jni_Lib_arg1(
    JNIEnv* env, jobject thiz, jint a);
void Java_com_maxwin_dab_jni_Lib_arg2(
    JNIEnv* env, jobject thiz, jint a, jint b);

Type 對應 Table

Type 對應 Table conti.

sig 晚點解釋

大部分使用方式

• CallStatic<type>Method
• Call<type>Method
• SetStatic<type>Field
• Set<type>Field
• GetStatic<type>Field
• Get<type>Field

實際使用時會遇到的(init)

package com.maxwin.tw;
class Yume {
}

jclass clz = env->FindClass("com/maxwin/tw/Yume");
jmethodID init = env->GetMethodID(clz, "<init>", "()V");
jobject yume = env->NewObject(clz, init);
// ...
env->DeleteLocalRef(yume);
env->DeleteLocalRef(clz);

new Yume();

實際使用時會遇到的(set value)

package com.maxwin.tw;
class Yume {
    int dreamCounts;
}

jfieldID dreamCountsField = env->GetFieldID(
    clz, "dreamCounts", "I");
env->SetIntField(yume, dreamCountsField, 101);

實際使用時會遇到的(call func)

package com.maxwin.tw;
class Yume {
    int dream(int a, int b) { return a + b; }
}

jmethodID dreamMethod = env->GetMethodID(
    clz, "dream", "(II)I");
jint dreams = env->CallIntMethod(yume, dreamMethod, 50, 51);

實際上最長使用到的

jfieldID GetFieldID(
    jclass clazz, const char *name, const char *sig)
jmethodID GetMethodID(
    jclass clazz, const char *name, const char *sig)

const char *sig?, Signature?

• Field sig
• Method sig

Type VS Sig Rule (Adv)

array sig

[ + type sig

byte -> B -> Array + B = [B

byte[];

"[B"

object sig

L + full class name + ;

String; // java.lang.String

"Ljava/lang/String;"

function sig

( + args sig + ) + return sig

void foo(int a, int b, int c) {}

"(III)V"

Type VS Sig Table (Adv)

More Prac I

int example1(int a, int b) {/*...*/}

"(II)I"

More Prac II

void example2(String a[]) {/*...*/}

"([Ljava/lang/String;)V"

C Hello World CMakeLists.txt

產生 libhello.so

cmake_minimum_required(VERSION 3.4.1)

add_library(
    hello SHARED
    hello-jni.c
)

# Include libraries needed for hello-jni lib
target_link_libraries(
    hello
    android
    log
)

Java 端 HelloJni.java

public class Lib {
    static {
        System.loadLibrary("hello");
    }
}

Proj layout

~/dab/app/src/main/jni4> tree
.
├── CMakeLists.txt
├── xxx.cpp
├── inc
│   └── API.h
└── jniLibs
    └── armeabi
        ├── libdabcontroller.so
        └── libdablibforexpartner.so

限制 cmake 最低版本為 3.4.1

cmake_minimum_required(VERSION 3.4.1)

確保有 log lib
log-lib=log

find_library(
    log-lib
    log
)

把 inc 加入到 header search path

include_directories(
    inc
)

ANDROID_ABI

不同手機 cpu abi 不同

# distribution_DIR=${CMAKE_SOURCE_DIR}/jniLibs/${ANDROID_ABI}
set(distribution_DIR ${CMAKE_SOURCE_DIR}/jniLibs/${ANDROID_ABI})

加入已編好的 .so

add_library(dabforex SHARED IMPORTED)
set_target_properties(dabforex PROPERTIES IMPORTED_LOCATION
    ${distribution_DIR}/libdablibforexpartner.so)

add_library(dabforamaryllo SHARED IMPORTED)
set_target_properties(dabforamaryllo PROPERTIES IMPORTED_LOCATION
    ${distribution_DIR}/libdabcontroller.so)

java setting

package com.maxwin.dab.jni;

public class Lib {
    static {
        System.loadLibrary("dablibforexpartner");
        System.loadLibrary("dabcontroller");
        System.loadLibrary("dabcontrollerdemo");
    }
}

Local Reference

object 相關類型會有產生 local ref
目前遇到的上限為 512
超過便會發生 JNI ERROR

// 需要在適當時機處理掉 
env->DeleteLocalRef(ref);

Reference Type(會產生 local ref)

• object
• string
• array
• throwable
• class

Value Type

基本型態以及

struct _jfieldID;                       /* opaque structure */
typedef struct _jfieldID* jfieldID;     /* field IDs */

struct _jmethodID;                      /* opaque structure */
typedef struct _jmethodID* jmethodID;   /* method IDs */

Global Reference

一樣要在適當時機釋放 ref
使用時機多為需要 長期/多次 使用

newRef = env->NewGlobalRef(ref);
env->DeleteGlobalRef(newRef);

pthread interact java main thread

vm->AttachCurrentThread(&env, NULL);
// ...

vm->DetachCurrentThread();

onload & onunload

可以在這兩個時機點 準備/釋放 globol ref

JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* vm, void* reserved) {
    JNIEnv* env;
    if (vm->GetEnv((void**)&env, JNI_VERSION_1_6) != JNI_OK) {
        return JNI_ERR; // JNI version not supported.
    }
    ctx.vm = vm;
    ctx.env = env;

    return JNI_VERSION_1_6;
}

JNIEXPORT void JNICALL JNI_OnUnload(JavaVM* vm, void* reserved) {
}

結論

1. androidTest
2. 自編
   • System.load(file.getAbsolutePath());
   • System.setProperty("java.library.path", libraryPath);