如何将我的NDK项目拆分为lib和app

Question

I have an NDK-based project (written mostly on C++) and I want to split its sources into two parts: "lib" (to be shared with other projects) and "app" (files specific to current project).

Now my Android.mk looks as follows:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := MyProj

MY_LIB_SOURCES := \
libfile1.cpp \
libfile2.cpp

MY_APP_SOURCES := \
appfile1.cpp \
appfile2.cpp

LOCAL_SRC_FILES += $(MY_LIB_SOURCES)
LOCAL_SRC_FILES += $(MY_APP_SOURCES)

LOCAL_STATIC_LIBRARIES := android_native_app_glue

include $(BUILD_SHARED_LIBRARY)

$(call import-module,android/native_app_glue)

The only reason for splitting is that I want to add/remove lib source file once, because now I have to change Android.mk for all projects which need sources from MY_LIB_SOURCES .

Do I have to create a separate project that would produce a shared library? Or should it be a static library? Or maybe it's possible to just #include somehow file that enumerates MY_LIB_SOURCES into Android.mk of each app?

Answer 1

You must divide your android.mk in two sections:

LOCAL_PATH := $(call my-dir)

## The lib ##
include $(CLEAR_VARS)
LOCAL_MODULE    := my_lib

SRC_LIB := $(wildcard $(LOCAL_PATH)/*.cpp)
LOCAL_SRC_FILES := $(SRC_LIB:$(LOCAL_PATH)/%=%)

include $(PREBUILT_SHARED_LIBRARY)

## The App ##
include $(CLEAR_VARS)
LOCAL_MODULE := my_app
LOCAL_CPP_EXTENSION := .cxx .cpp .cc

LOCAL_SRC_FILES := \
    appfile1.cpp \
    appfile2.cpp

LOCAL_STATIC_LIBRARIES := android_native_app_glue
LOCAL_SHARED_LIBRARIES := my_lib
LOCAL_LDLIBS    += -landroid

include $(BUILD_EXECUTABLE)

$(call import-module,android/native_app_glue)

If you want static library you have only to change include $(PREBUILT_SHARED_LIBRARY) to include $(PREBUILT_STATIC_LIBRARY) and LOCAL_SHARED_LIBRARIES := my_lib to LOCAL_STATIC_LIBRARIES += my_lib

Answer 2

We usually create a separate folder for library sources, eg

project
  jni
    appfile1.cpp
    appfile2.cpp
    Android.mk (1)

my_lib
  libfile1.cpp
  libfile2.cpp
  Android.mk   (2)

This is the first ( application ) Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := MyProj

MY_APP_SOURCES := \
appfile1.cpp \
appfile2.cpp

LOCAL_SRC_FILES += $(MY_APP_SOURCES)

LOCAL_STATIC_LIBRARIES := android_native_app_glue
LOCAL_STATIC_LIBRARIES += MyLib

include $(BUILD_SHARED_LIBRARY)

include $(LOCAL_PATH)/../../my_lib/Android.mk
$(call import-module,android/native_app_glue)

This is the second ( library ) Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := MyLib

MY_LIB_SOURCES := \
libfile1.cpp \
libfile2.cpp

LOCAL_SRC_FILES += $(MY_LIB_SOURCES)

include $(BUILD_STATIC_LIBRARY)

Using the Andorid.mk name for MyLib is by convention; you could use some other file name, and change the include statement (line 17 of the first Android.mk file) accordingly.

You could also use the same $(call import-module) syntax, like

$(call import-module,my_lib)

But to do so, you must provide a NDK_MODULE_PATH environment variable that includes $(LOCAL_PATH)/../../ .

Your library will be rebuilt anew for each app (project) that includes it - either with the first naïve include method, or with $(call import-module) method. You can provide a prebuilt static library, but this is a different story.