记得前阵子编译so库直接使用ndk-build搞定，今天使用却报错如下：

$ ndk-build
Android NDK: Could not find application project directory !    
Android NDK: Please define the NDK_PROJECT_PATH variable to point to it.    
/opt/android-ndk-r10b/build/core/build-local.mk:148: *** Android NDK: Aborting    .  Stop.

高人支招如下：

You need to specify 3 things.
NDK_PROJECT_PATH - the location of your project
NDK_APPLICATION_MK - the path of the Application.mk file
APP_BUILD_SCRIPT - the path to the Android.mk file

These are needed to override the default values of the build script, which expects things to be in the jni folder.

When calling ndk-build use
ndk-build NDK_PROJECT_PATH=/path/to/proj NDK_APPLICATION_MK=/path/to/Application.mk

In Application.mk add
APP_BUILD_SCRIPT := /path/to/Android.mk

首先第一步，在Application中加入Android.mk路径
比如这两个文件是同级的:

APP_BUILD_SCRIPT := Android.mk

第二步，直接编译：

$ ndk-build NDK_PROJECT_PATH=. NDK_APPLICATION_MK=Application.mk
[armeabi-v7a] Compile++ thumb: detection_and_recognition_lib <= DetectionAndRecognition.cpp
[armeabi-v7a] Prebuilt       : libopencv_java.so <= /home/linc/workspace/lab/OpenCV-android-sdk-2.4.11/sdk/native/jni/../libs/armeabi-v7a/
[armeabi-v7a] SharedLibrary  : libdetection_and_recognition_lib.so
/opt/android-ndk-r10b/toolchains/arm-linux-androideabi-4.6/prebuilt/linux-x86_64/bin/../lib/gcc/arm-linux-androideabi/4.6/../../../../arm-linux-androideabi/bin/ld: warning: hidden symbol '__aeabi_atexit' in /opt/android-ndk-r10b/sources/cxx-stl/gnu-libstdc++/4.6/libs/armeabi-v7a/thumb/libgnustl_static.a(atexit_arm.o) is referenced by DSO ./obj/local/armeabi-v7a/libopencv_java.so
[armeabi-v7a] Install        : libdetection_and_recognition_lib.so => libs/armeabi-v7a/libdetection_and_recognition_lib.so
[armeabi-v7a] Prebuilt       : libnative_camera_r4.3.0.so <= /home/linc/workspace/lab/OpenCV-android-sdk-2.4.11/sdk/native/jni/../libs/armeabi-v7a/
[armeabi-v7a] Install        : libnative_camera_r4.3.0.so => libs/armeabi-v7a/libnative_camera_r4.3.0.so
[armeabi-v7a] Prebuilt       : libnative_camera_r4.4.0.so <= /home/linc/workspace/lab/OpenCV-android-sdk-2.4.11/sdk/native/jni/../libs/armeabi-v7a/
[armeabi-v7a] Install        : libnative_camera_r4.4.0.so => libs/armeabi-v7a/libnative_camera_r4.4.0.so
[armeabi-v7a] Install        : libopencv_java.so => libs/armeabi-v7a/libopencv_java.so
[x86] Compile++      : detection_and_recognition_lib <= DetectionAndRecognition.cpp
[x86] Prebuilt       : libopencv_java.so <= /home/linc/workspace/lab/OpenCV-android-sdk-2.4.11/sdk/native/jni/../libs/x86/
[x86] SharedLibrary  : libdetection_and_recognition_lib.so
[x86] Install        : libdetection_and_recognition_lib.so => libs/x86/libdetection_and_recognition_lib.so
[x86] Prebuilt       : libnative_camera_r4.3.0.so <= /home/linc/workspace/lab/OpenCV-android-sdk-2.4.11/sdk/native/jni/../libs/x86/
[x86] Install        : libnative_camera_r4.3.0.so => libs/x86/libnative_camera_r4.3.0.so
[x86] Prebuilt       : libnative_camera_r4.4.0.so <= /home/linc/workspace/lab/OpenCV-android-sdk-2.4.11/sdk/native/jni/../libs/x86/
[x86] Install        : libnative_camera_r4.4.0.so => libs/x86/libnative_camera_r4.4.0.so
[x86] Install        : libopencv_java.so => libs/x86/libopencv_java.so

各位大虾也许看出来了，我在编译OpenCV相关的项目。而现在的设备选型已经涵盖了x86架构，所以编译时要选择x86指令集编译。在Application.mk中注明如下：

APP_ABI := armeabi-v7a x86

参考：
http://stackoverflow.com/questions/14156596/ndk-cant-find-the-application-directory