Android7.0 Launcher3 无法导入SystemProperties

今天遇到一个问题：在Launcher3，中添加SystemProperties功能，始终编译不过，报错如下：

ERROR: /home/zhiwu/sungq/M970/packages/apps/Launcher3/src/com/android/launcher3/Launcher.java:80: The import android.os.SystemProperties cannot be resolved
ERROR: /home/zhiwu/sungq/M970/packages/apps/Launcher3/src/com/android/launcher3/Launcher.java:2780: SystemProperties cannot be resolved
ERROR: /home/zhiwu/sungq/M970/packages/apps/Launcher3/src/com/android/launcher3/Launcher.java:2781: SystemProperties cannot be resolved

到framework下面查找位置：

framework/base/core/java/android/os/SystemProperties.java

为什么这个位置下其他的文件都可以找到，唯独SystemProperties找不到，

最后对比其他可以使用SystemProperties的应用，发现LOCAL_JAVA_LIBRARIES := framework这个属性

在Launcher3的android.mk里面没有

最后在android.mk里加上LOCAL_JAVA_LIBRARIES := framework这个，就可以编译通过了。

下面附上Android.mk的源码，供查询

LOCAL_PATH := $(call my-dir)

#
# Build app code.
#
include $(CLEAR_VARS)

LOCAL_MODULE_TAGS := optional

LOCAL_JAVA_LIBRARIES := framework
LOCAL_STATIC_JAVA_LIBRARIES := \
    android-support-v4 \
    android-support-v7-recyclerview

LOCAL_SRC_FILES := $(call all-java-files-under, src) \
    $(call all-java-files-under, WallpaperPicker/src) \
    $(call all-proto-files-under, protos)

LOCAL_SRC_FILES += src/com/qti/launcherunreadservice/IGetUnreadNumber.aidl

LOCAL_RESOURCE_DIR := $(LOCAL_PATH)/WallpaperPicker/res \
    $(LOCAL_PATH)/res \
    frameworks/support/v7/recyclerview/res

LOCAL_PROGUARD_FLAG_FILES := proguard.flags

LOCAL_PROTOC_OPTIMIZE_TYPE := nano
LOCAL_PROTOC_FLAGS := --proto_path=$(LOCAL_PATH)/protos/
LOCAL_AAPT_FLAGS := \
    --auto-add-overlay \
    --extra-packages android.support.v7.recyclerview

LOCAL_SDK_VERSION := current
LOCAL_PACKAGE_NAME := Launcher3
LOCAL_PRIVILEGED_MODULE := true
#LOCAL_CERTIFICATE := shared

LOCAL_OVERRIDES_PACKAGES := Home Launcher2

include $(BUILD_PACKAGE)


#
# Launcher proto buffer jar used for development
#
include $(CLEAR_VARS)

LOCAL_SRC_FILES := $(call all-proto-files-under, protos)

LOCAL_PROTOC_OPTIMIZE_TYPE := nano
LOCAL_PROTOC_FLAGS := --proto_path=$(LOCAL_PATH)/protos/

LOCAL_MODULE_TAGS := optional
LOCAL_MODULE := launcher_proto_lib
LOCAL_IS_HOST_MODULE := true
LOCAL_STATIC_JAVA_LIBRARIES := host-libprotobuf-java-nano

include $(BUILD_HOST_JAVA_LIBRARY)

include $(call all-makefiles-under,$(LOCAL_PATH))