Android开发实践：Android.mk模板

关于Android NDK开发的文章已经比较多了，我的博客中也分享了很多NDK开发相关经验和技巧，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。