NDK-build vs Android Studio NDK Build

Question

要运行某些本机代码，您可以执行ndk-build命令，但是如果Eclipse或Android Studio IDE在编译时自动执行此命令，或者当我通过以下方式编译代码时ndk-build命令与上述IDE有何关系，我感到困惑月食还是机器人工作室？

Answer 1

For eclipse, there are already too many online sources related to it, so I will talk about Android Studio here.

If you don't have your onw native files (C++,C) in your project, just put the .a or .so native libraries in the src/main/jniLibs folders and you don't have to modify anything in the gradle file. The system will do everything for you automatically.

If you have your own native files and have put them in the src/main/jni folder, then you have to create your own makefiles and put them in the jni folder as well. You also have to modify the gradle file in your app module.

Here is what I did for a face detection sample of opencv, and I got the original code from this wonderful post( Here ), which was actually modified from another one's method for simpler execution. The philosophy is rather simple: compile the native source codes and put the generated .so/.a library into the jniLibs folder:

My project structure: Project Structure

My makefiles (make sure you have the original sdk of the library for reference in the makefile):

Android.mk:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

OPENCV_CAMERA_MODULES:=on
OPENCV_INSTALL_MODULES:=on
OPENCV_LIB_TYPE:=SHARED
include /home/ng/Desktop/OpenCV-android-sdk/sdk/native/jni/OpenCV.mk

LOCAL_SRC_FILES  := DetectionBasedTracker_jni.cpp
LOCAL_C_INCLUDES += $(LOCAL_PATH)
LOCAL_LDLIBS     += -llog -ldl

LOCAL_MODULE     := detection_based_tracker

include $(BUILD_SHARED_LIBRARY)

Application.mk:

    APP_STL := gnustl_static
    APP_CPPFLAGS := -frtti -fexceptions
    APP_ABI := armeabi-v7a armeabi
    APP_PLATFORM := android-19

My gradle.build file in the app module:

apply plugin: 'com.android.application'
android {
    compileSdkVersion 23
    buildToolsVersion "23.0.1"

    defaultConfig {
        applicationId "org.opencv.samples.facedetect"
        minSdkVersion 14
        targetSdkVersion 19
        versionCode 1
        versionName "1.0"
    }
    sourceSets.main.jni.srcDirs = []

    task ndkBuild(type: Exec, description: 'Compile JNI source via NDK') {
       // ndkDir = project.plugins.findPlugin('com.android.application').getNdkFolder()
        commandLine "$ndkDir/ndk-build",
                'NDK_PROJECT_PATH=build/intermediates/ndk',
                'NDK_LIBS_OUT=src/main/jniLibs',
                'APP_BUILD_SCRIPT=src/main/jni/Android.mk',
                'NDK_APPLICATION_MK=src/main/jni/Application.mk'
    }

    tasks.withType(JavaCompile) {
        compileTask -> compileTask.dependsOn ndkBuild
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.1.0'
    compile project(':openCVLibrary300')
}

You don't actually have to change other gradle files for compiling the native part of the project. You could also compile the native sources codes by command line and put the .so files back to the jniLibs folder. This also works. I hope this could help in your problem.

Answer 2

如果需要，可以使用Terminal命令进行编译，否则可以将两个IDE配置为自动执行

Answer 3

Today Android-Studio (Canary) Preview 1.3 RC1 got released with jni/ndk support out of the box. No need to call commandline tools anymore.

https://sites.google.com/a/android.com/tools/download/studio/canary/latest

Release Notes: https://sites.google.com/a/android.com/tools/recent/androidstudiowithandroidndkpreviewsupportavailable