Android.mk开发模板

今天简单写了一个 Android.mk 的示例模板，供初学者参考。
本模板主要给大家示例 Android NDK 开发中的如下几个问题：

1. 如何自动添加需要编译的源文件列表
2. 如何添加第三方静态库、动态库的依赖
3. 如何构造一个完整的NDK工程框架

假设我们的项目依赖 libmath.a, libjson.a, libffmpeg.so 这几个第三方库文件，项目包含如下几个模块：algorithm，core，network，utils，tests，每个模块都有若干个.c/.h文件，我们要把整个工程编译为动态库，并通过 native_sdk.c 中的函数向Java层提供调用接口。
那么，我们可以对 Android 工程的 jni 目录，做如下划分：

对应的 Android.mk 文件的写法示例如下：

LOCAL_PATH := $(call my-dir)
3RD_INC_DIR = $(LOCAL_PATH)/3rd/inc
3RD_LIB_DIR = $(LOCAL_PATH)/3rd/libs
 
# Prebuild the 3rd libraries 
 
include $(CLEAR_VARS)
LOCAL_MODULE := math
LOCAL_SRC_FILES := $(3RD_LIB_DIR)/libmath.a
include $(PREBUILT_STATIC_LIBRARY)
 
include $(CLEAR_VARS)
LOCAL_MODULE := json
LOCAL_SRC_FILES := $(3RD_LIB_DIR)/libjson.a
include $(PREBUILT_STATIC_LIBRARY)
 
include $(CLEAR_VARS)
LOCAL_MODULE := ffmpeg
LOCAL_SRC_FILES := $(3RD_LIB_DIR)/libffmpeg.so
include $(PREBUILT_SHARED_LIBRARY)
 
# Build native sdk 
 
include $(CLEAR_VARS)    
 
LOCAL_MODULE := native_sdk
 
LOCAL_SRC_FILES := \
    $(subst $(LOCAL_PATH)/,,$(wildcard $(LOCAL_PATH)/src/algorithm/*.c))  \
    $(subst $(LOCAL_PATH)/,,$(wildcard $(LOCAL_PATH)/src/core/*.c))  \
    $(subst $(LOCAL_PATH)/,,$(wildcard $(LOCAL_PATH)/src/network/*.c)) \
    $(subst $(LOCAL_PATH)/,,$(wildcard $(LOCAL_PATH)/src/utils/*.c)) \
    $(subst $(LOCAL_PATH)/,,$(wildcard $(LOCAL_PATH)/src/*.c))  
    
LOCAL_C_INCLUDES := $(3RD_INC_DIR)
LOCAL_C_INCLUDES := $(LOCAL_PATH)/src 
LOCAL_C_INCLUDES := $(LOCAL_PATH)/src/algorithm
LOCAL_C_INCLUDES += $(LOCAL_PATH)/src/core
LOCAL_C_INCLUDES += $(LOCAL_PATH)/src/network
LOCAL_C_INCLUDES += $(LOCAL_PATH)/src/utils
 
LOCAL_CFLAGS := -DANDROID                                      
LOCAL_LDLIBS := -llog 
 
LOCAL_STATIC_LIBRARIES := math json
LOCAL_SHARED_LIBRARIES := ffmpeg
 
include $(BUILD_SHARED_LIBRARY)
 
 
# Build tests
 
include $(CLEAR_VARS)    
LOCAL_MODULE := test.out
LOCAL_SRC_FILES := $(subst $(LOCAL_PATH)/,,$(wildcard $(LOCAL_PATH)/tests/*.c)) 
LOCAL_CFLAGS := -DANDROID 
LOCAL_C_INCLUDES := $(LOCAL_PATH)/src 
LOCAL_LDLIBS := -llog -fPIE -pie
LOCAL_SHARED_LIBRARIES:= native_sdk
include $(BUILD_EXECUTABLE)

对于 Android.mk 而言，如果要依赖第三方库文件，则必须添加 PREBUILT_XXXX_LIBRARY 进行预编译，LOCAL_SRC_FILES 宏给出了需要编译的源文件列表，这里我通过 subst和wildcard 这两个函数，实现了自动扫描指定目录下的源文件，最后，通过 BUILD_EXECUTABLE 编译出可以运行于adb shell命令行的可执行程序，用于做代码的单元测试。