JAVA引用aar_Android.mk aar引用过程

网上很多教程都有问题，很多人这样引用aar包：

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

.....

LOCAL_STATIC_JAVA_AAR_LIBRARIES:=

LOCAL_AAPT_FLAGS := \

--auto-add-overlay \

--extra-packages

include $(BUILD_PACKAGE)

include $(CLEAR_VARS)

LOCAL_PREBUILT_STATIC_JAVA_LIBRARIES := :libs/.aar

include $(BUILD_MULTI_PREBUILT)

首先，先给结论，这种方式在Android P上是有问题的，这样是引用不到aar中的资源文件。

看源码：

//multi_prebuilt.mk

define auto-prebuilt-boilerplate

$(if $(filter %: :%,$(1)), \

$(error $(LOCAL_PATH): Leading or trailing colons in "$(1)")) \

$(foreach t,$(1), \

$(eval include $(CLEAR_VARS)) \

$(eval LOCAL_IS_HOST_MODULE := $(2)) \

$(eval LOCAL_MODULE_CLASS := $(3)) \

$(eval LOCAL_MODULE_TAGS := $(4)) \

$(eval OVERRIDE_BUILT_MODULE_PATH := $(5)) \

$(eval LOCAL_UNINSTALLABLE_MODULE := $(6)) \

$(eval tw := $(subst :, ,$(strip $(t)))) \

$(if $(word 3,$(tw)),$(error $(LOCAL_PATH): Bad prebuilt filename '$(t)')) \

$(if $(word 2,$(tw)), \

$(eval LOCAL_MODULE := $(word 1,$(tw))) \

$(eval LOCAL_SRC_FILES := $(word 2,$(tw))) \

, \

$(eval LOCAL_MODULE := $(basename $(notdir $(t)))) \

$(eval LOCAL_SRC_FILES := $(t)) \

) \

$(if $(7), \

$(eval LOCAL_BUILT_MODULE_STEM := $(7)) \

, \

$(if $(word 2,$(tw)), \

$(eval LOCAL_BUILT_MODULE_STEM := $(LOCAL_MODULE)$(suffix $(LOCAL_SRC_FILES))) \

, \

$(eval LOCAL_BUILT_MODULE_STEM := $(notdir $(LOCAL_SRC_FILES))) \

) \

) \

$(eval LOCAL_MODULE_SUFFIX := $(suffix $(LOCAL_SRC_FILES))) \

$(eval LOCAL_STRIP_MODULE := $(8)) \

$(eval include $(BUILD_PREBUILT)) \

)

endef

这是其中的一段主要代码，不用理解他的具体含义，我们从倒数第三行可以看出，BUILD_MULTI_PREBUILT最终是对每个值分别调用了BUILD_PREBUILT，我们再看BUILD_PREBUILT，它是定义在prebuilt_internal.mk中

my_src_aar := $(filter %.aar, $(my_prebuilt_src_file))

ifneq ($(my_src_aar),)

# This is .aar file, archive of classes.jar and Android resources.

........

my_src_jar := $(intermediates.COMMON)/aar/classes.jar

my_src_proguard_options := $(intermediates.COMMON)/aar/proguard.txt

$(my_src_jar) : .KATI_IMPLICIT_OUTPUTS := $(my_src_proguard_options)

$(my_src_jar) : $(my_src_aar)

$(hide) rm -rf $(dir $@) && mkdir -p $(dir $@) $(dir $@)/res

$(hide) unzip -qo -d $(dir $@) $<

# Make sure the extracted classes.jar has a new timestamp.

$(hide) touch $@

# Make sure the proguard file exists and has a new timestamp.

$(hide) touch $(dir $@)/proguard.txt

这段代码，是对aar库进行解压。

ifdef LOCAL_AAPT2_ONLY

LOCAL_USE_AAPT2 := true

endif

ifdef LOCAL_USE_AAPT2

ifneq ($(my_src_aar),)

.......

my_res_package := $(intermediates.COMMON)/package-res.apk

# We needed only very few PRIVATE variables and aapt2.mk input variables. Reset the unnecessary ones.

$(my_res_package): PRIVATE_AAPT2_CFLAGS :=

$(my_res_package): PRIVATE_AAPT_FLAGS := --static-lib --no-static-lib-packages --auto-add-overlay

$(my_res_package): PRIVATE_ANDROID_MANIFEST := $(intermediates.COMMON)/aar/AndroidManifest.xml

$(my_res_package): PRIVATE_AAPT_INCLUDES := $(framework_res_package_export)

$(my_res_package): PRIVATE_SOURCE_INTERMEDIATES_DIR :=

$(my_res_package): PRIVATE_PROGUARD_OPTIONS_FILE :=

$(my_res_package): PRIVATE_DEFAULT_APP_TARGET_SDK :=

$(my_res_package): PRIVATE_DEFAULT_APP_TARGET_SDK :=

$(my_res_package): PRIVATE_PRODUCT_AAPT_CONFIG :=

$(my_res_package): PRIVATE_PRODUCT_AAPT_PREF_CONFIG :=

$(my_res_package): PRIVATE_TARGET_AAPT_CHARACTERISTICS :=

$(my_res_package) : $(framework_res_package_export)

full_android_manifest :=

my_res_resources :=

my_overlay_resources :=

my_compiled_res_base_dir := $(intermediates.COMMON)/flat-res

R_file_stamp :=

proguard_options_file :=

my_generated_res_dirs := $(intermediates.COMMON)/aar/res

my_generated_res_dirs_deps := $(my_src_jar)

include $(BUILD_SYSTEM)/aapt2.mk

# Make sure my_res_package is created when you run mm/mmm.

$(built_module) : $(my_res_package)

endif # $(my_src_aar)

endif # LOCAL_USE_AAPT2

这里看到，只有当定义LOCAL_USE_AAPT2时，才会调用aapt2.mk，将aar解压后的资源打包成package-res.apk，而我们举例的multi_prebuilt.mk代码中，可以看到两个信息：

1、调用了include $(CLEAR_VARS)

2、未定义LOCAL_USE_AAPT2

由此可以得出结论，无论我们如何在BUILD_MULTI_PREBUILT中引用aar库，都不能生成package-res.apk，这意味着我们下面的代码将不会生效(至少在Android 9上是这样)

LOCAL_AAPT_FLAGS := \

--auto-add-overlay \

--extra-packages

我们的代码将引用不到aar中的资源。

要想引用到，必须采用BUILD_PREBUILT，并且需要在里面声明LOCAL_USE_AAPT2 := true

那有人会问，我不用appt2，能引用到aar中的资源吗？答案是：可以，可是这样会出现很多错误，至少我解决不了。

当我们使用LOCAL_STATIC_JAVA_AAR_LIBRARIES时，如果没有定义LOCAL_USE_AAPT2，才会去引用aar/res

android_manifest.mk

LOCAL_STATIC_JAVA_AAR_LIBRARIES := $(strip $(LOCAL_STATIC_JAVA_AAR_LIBRARIES))

ifdef LOCAL_STATIC_JAVA_AAR_LIBRARIES

my_full_libs_manifest_deps += $(foreach lib, $(LOCAL_STATIC_JAVA_AAR_LIBRARIES),\

$(call intermediates-dir-for,JAVA_LIBRARIES,$(lib),,COMMON)/aar/classes.jar)

my_full_libs_manifest_files += $(foreach lib, $(LOCAL_STATIC_JAVA_AAR_LIBRARIES),\

$(call intermediates-dir-for,JAVA_LIBRARIES,$(lib),,COMMON)/aar/AndroidManifest.xml)

# With aapt2, we'll link in the built resource from the AAR.

ifndef LOCAL_USE_AAPT2

LOCAL_RESOURCE_DIR += $(foreach lib, $(LOCAL_STATIC_JAVA_AAR_LIBRARIES),\

$(call intermediates-dir-for,JAVA_LIBRARIES,$(lib),,COMMON)/aar/res)

endif # LOCAL_USE_AAPT2

endif # LOCAL_STATIC_JAVA_AAR_LIBRARIES