[Android] Write a JNI interface for your Android application

Write a JNI Interface for Android Application

Jing (mqJing@msn.com)

Download: hellojni.zip

Outline
Use Your Native Function

• [Java] Write your java code -> apk

Create the Library

• [C header] Generate the function prototype
• [C] Implement the function
• [Android] Write a make file
• Put all files in to the “external” or “development” directory
• [Make] goto the source root and make the module

Testing

• Build & Burning the Image
• adb install your_application.apk

Content
Step 1: [Java] Write your java code

package name: hellojni.hellojni

class name:hellojni.java

*

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Create the Library
Step 2: [C header] Generate the function prototype

a. Build the code: hellojni

b. Make sure you path: at bin

a. Build the code to generate class file (You can use Eclipse to do this) b. Make sure your path: bin bin | ---hellojni | ---- hellojni | ----- hellojni.class c. Generate the header file Command: javah -jni . ex: bin\>javah hellojni.hellojni.hellojni Result:

Step 3: [C] Implement the function

hellojni.c

#include #define LOG_TAG "ABC_lib" #undef LOG #include JNIEXPORT jint JNICALL Java_hellojni_hellojni_hellojni_addTest(JNIEnv *env, jclass cls, jint x, jint y){ // 你可以用 adb 連進 device, 用 logcat 看資料 LOGD("Java_hellojni_hellojni_hellojni_addTest"); return x+y; }

Step 4: [Android] Write a make file

Android.mk

# 一開始要加這段 LOCAL_PATH:= $(call my-dir) include $(CLEAR_VARS) # 指定要編譯的原始檔 LOCAL_SRC_FILES:= \ hellojni.c # 設定 .h 檔搜尋目錄 LOCAL_C_INCLUDES := \ $(JNI_H_INCLUDE) # 這個 .c 檔要使用 libutils library LOCAL_SHARED_LIBRARIES := \ libutils # 不使用 prelink LOCAL_PRELINK_MODULE := false # [輸出] 表明需要編成 share libaray # 會產生 out/target/product/xxx/obj/lib/libhellojni.so LOCAL_MODULE := libhellojni include $(BUILD_SHARED_LIBRARY)

Step 5: Put all files in to the “external” or “development” directory


Step 6: [Make] goto the source root and make the module
Command:
$make <你定義的 LOCAL_MODULE name>
Ex:
$make libhellojni

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Testing
Step 1: build image
Step 2: burn image
Step 3: adb install your_application.apk

Reference:

1. http://www.top-e.org/jiaoshi/html/?168.html