一撕氧、Android.mk介紹
Android.mk是Android提供的一種makefile文件，用來指定諸如編譯生成so庫名喇完、引用的頭文件目錄、需要編譯的.c/.cpp文件和.a靜態(tài)庫文件等锦溪。要掌握jni，就必須熟練掌握Android.mk的語法規(guī)范刻诊。
它的基本格式如下：
[cpp]view plaincopyprint?
LOCAL_PATH := $(call my-dir)?
include $(CLEAR_VARS)?
................?
LOCAL_xxx? ? ? := xxx?
LOCAL_MODULE? ? := hello-jni?
LOCAL_SRC_FILES := hello-jni.c?
LOCAL_xxx? ? ? := xxx?
................?
include $(BUILD_SHARED_LIBRARY)?
LOCAL_PATH變量制定了該.mk的路徑，$(call my-dir)調用NDK內部的函數(shù)獲得當前.mk文件的路徑
include $(CLEAR_VARS)清空了除了LOCAL_PATH之外的所有LOCAL_xxx變量的值
省略號中間就是對于模塊參數(shù)的設置坏逢，主要包括：模塊名字、模塊源文件是整、模塊類型、編譯好的模塊存放位置民假、以及編譯的平臺等
include $(BUILD_xxx_xxx)執(zhí)行NDK的默認腳本，它會收集include $(CLEAR_VARS)腳本后所有定義的LOCAL_xxx變量羊异，然后根據(jù)它們來生成模塊。
二野舶、Android.mk語法詳解
LOCAL_PATH := $(call my-dir)
每個Android.mk文件必須以定義LOCAL_PATH為開始易迹。它用于在開發(fā)tree中查找源文件平道。宏my-dir 則由Build System提供。返回包含Android.mk的目錄路徑。
include $(CLEAR_VARS)
CLEAR_VARS 變量由Build System提供窘疮。并指向一個指定的GNU Makefile袋哼，由它負責清理很多LOCAL_xxx.
例如：LOCAL_MODULE, LOCAL_SRC_FILES, LOCAL_STATIC_LIBRARIES等等闸衫。但不清理LOCAL_PATH.
這個清理動作是必須的，因為所有的編譯控制文件由同一個GNU Make解析和執(zhí)行蔚出，其變量是全局的弟翘。所以清理后才能避免相互影響身冬。
LOCAL_MODULE? ? := hello-jni
LOCAL_MODULE模塊必須定義衅胀，以表示Android.mk中的每一個模塊酥筝。名字必須唯一且不包含空格滚躯。Build System會自動添加適當?shù)那熬Y和后綴嘿歌。例如掸掏，foo宙帝，要產(chǎn)生動態(tài)庫丧凤，則生成libfoo.so. 但請注意：如果模塊名被定為：libfoo.則生成libfoo.so. 不再加前綴
LOCAL_MODULE_PATH :=$(TARGET_ROOT_OUT) 指定最后生成的模塊的目標地址
TARGET_ROOT_OUT:根文件系統(tǒng)步脓，路徑為out/target/product/generic/root
TARGET_OUT:system文件系統(tǒng)愿待，路徑為out/target/product/generic/system
TARGET_OUT_DATA:data文件系統(tǒng)靴患，路徑為out/target/product/generic/data
除了上面的這些仍侥，NDK還提供了很多其他的TARGET_XXX_XXX變量鸳君，用于將生成的模塊拷貝到輸出目錄的不同路徑
默認是TARGET_OUT
LOCAL_SRC_FILES := hello-jni.c
LOCAL_SRC_FILES變量必須包含將要打包如模塊的C/C++ 源碼农渊。不必列出頭文件或颊，build System 會自動幫我們找出依賴文件砸紊。缺省的C++源碼的擴展名為.cpp. 也可以修改囱挑，通過LOCAL_CPP_EXTENSION
include $(BUILD_SHARED_LIBRARY)
BUILD_SHARED_LIBRARY：是Build System提供的一個變量醉顽，指向一個GNU Makefile Script看铆。
它負責收集自從上次調用 include $(CLEAR_VARS)? 后的所有LOCAL_XXX信息徽鼎。并決定編譯為什么。
BUILD_STATIC_LIBRARY? ? ：編譯為靜態(tài)庫否淤。
BUILD_SHARED_LIBRARY ：編譯為動態(tài)庫
BUILD_EXECUTABLE? ? ? ? ? ：編譯為Native C可執(zhí)行程序?
BUILD_PREBUILT? ? ? ? ? ? ? ? ：該模塊已經(jīng)預先編譯
NDK還定義了很多其他的BUILD_XXX_XXX變量悄但，它們用來指定模塊的生成方式石抡。
三檐嚣、使用示例
[cpp]view plaincopyprint?
#編譯靜態(tài)庫? ?
LOCAL_PATH := $(call my-dir)? ?
include $(CLEAR_VARS)? ?
LOCAL_MODULE = libhellos? ?
LOCAL_CFLAGS = $(L_CFLAGS)? ?
LOCAL_SRC_FILES = hellos.c? ?
LOCAL_C_INCLUDES = $(INCLUDES)? ?
LOCAL_SHARED_LIBRARIES := libcutils? ?
LOCAL_COPY_HEADERS_TO := libhellos? ?
LOCAL_COPY_HEADERS := hellos.h? ?
include $(BUILD_STATIC_LIBRARY)? ?
#編譯動態(tài)庫? ?
LOCAL_PATH := $(call my-dir)? ?
include $(CLEAR_VARS)? ?
LOCAL_MODULE = libhellod? ?
LOCAL_CFLAGS = $(L_CFLAGS)? ?
LOCAL_SRC_FILES = hellod.c? ?
LOCAL_C_INCLUDES = $(INCLUDES)? ?
LOCAL_SHARED_LIBRARIES := libcutils? ?
LOCAL_COPY_HEADERS_TO := libhellod? ?
LOCAL_COPY_HEADERS := hellod.h? ?
include $(BUILD_SHARED_LIBRARY)? ?
#使用靜態(tài)庫? ?
LOCAL_PATH := $(call my-dir)? ?
include $(CLEAR_VARS)? ?
LOCAL_MODULE := hellos? ?
LOCAL_STATIC_LIBRARIES := libhellos? ?
LOCAL_SHARED_LIBRARIES :=? ?
LOCAL_LDLIBS += -ldl? ?
LOCAL_CFLAGS := $(L_CFLAGS)? ?
LOCAL_SRC_FILES := mains.c? ?
LOCAL_C_INCLUDES := $(INCLUDES)? ?
include $(BUILD_EXECUTABLE)? ?
#使用動態(tài)庫? ?
LOCAL_PATH := $(call my-dir)? ?
include $(CLEAR_VARS)? ?
LOCAL_MODULE := hellod? ?
LOCAL_MODULE_TAGS := debug? ?
LOCAL_SHARED_LIBRARIES := libc libcutils libhellod? ?
LOCAL_LDLIBS += -ldl? ?
LOCAL_CFLAGS := $(L_CFLAGS)? ?
LOCAL_SRC_FILES := maind.c? ?
LOCAL_C_INCLUDES := $(INCLUDES)? ?
include $(BUILD_EXECUTABLE)? ?
#拷貝文件到指定目錄?
LOCAL_PATH := $(call my-dir)?
include $(CLEAR_VARS)?
LOCAL_MODULE := bt_vendor.conf?
LOCAL_MODULE_CLASS := ETC?
LOCAL_MODULE_PATH := $(TARGET_OUT)/etc/bluetooth?
LOCAL_MODULE_TAGS := eng?
LOCAL_SRC_FILES := $(LOCAL_MODULE)?
include $(BUILD_PREBUILT)?
#拷貝動態(tài)庫到指定目錄?
LOCAL_PATH := $(call my-dir)?
include $(CLEAR_VARS)?
#the data or lib you want to copy?
LOCAL_MODULE := libxxx.so?
LOCAL_MODULE_CLASS := SHARED_LIBRARIES?
LOCAL_MODULE_PATH := $(ANDROID_OUT_SHARED_LIBRARIES)?
LOCAL_SRC_FILES := lib/$(LOCAL_MODULE )?
OVERRIDE_BUILD_MODULE_PATH := $(TARGET_OUT_INTERMEDIATE_LIBRARIES)?
include $(BUILD_PREBUILT)?
