一、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、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。要掌握jni，就必須熟練掌握Android.mk的語法規(guī)范。

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(diào)用NDK內(nèi)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(shè)置，主要包括：模塊名字、模塊源文件、模塊類型、編譯好的模塊存放位置、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，然后根據(jù)它們來生成模塊。

二、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。它用于在開發(fā)tree中查找源文件。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。并指向一個指定的GNU Makefile，由它負責清理很多LOCAL_xxx.

例如：LOCAL_MODULE, LOCAL_SRC_FILES, LOCAL_STATIC_LIBRARIES等等。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，其變量是全局的。所以清理后才能避免相互影響。

LOCAL_MODULE? ? := hello-jni

LOCAL_MODULE模塊必須定義，以表示Android.mk中的每一個模塊。名字必須唯一且不包含空格。Build System會自動添加適當?shù)那熬Y和后綴。例如，foo，要產(chǎn)生動態(tài)庫，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)，路徑為out/target/product/generic/root

TARGET_OUT:system文件系統(tǒng)，路徑為out/target/product/generic/system

TARGET_OUT_DATA:data文件系統(tǒng)，路徑為out/target/product/generic/data

除了上面的這些，NDK還提供了很多其他的TARGET_XXX_XXX變量，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。不必列出頭文件，build System 會自動幫我們找出依賴文件。缺省的C++源碼的擴展名為.cpp. 也可以修改，通過LOCAL_CPP_EXTENSION

include $(BUILD_SHARED_LIBRARY)

BUILD_SHARED_LIBRARY：是Build System提供的一個變量，指向一個GNU Makefile Script。

它負責收集自從上次調(diào)用 include $(CLEAR_VARS)? 后的所有LOCAL_XXX信息。并決定編譯為什么。

BUILD_STATIC_LIBRARY? ? ：編譯為靜態(tài)庫。

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(yù)先編譯

NDK還定義了很多其他的BUILD_XXX_XXX變量，它們用來指定模塊的生成方式。

三、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)?