Android 资源覆盖机制

Overlay Mechanism

android有一个资源覆盖机制，在不修改主体源代码的情况下实现资源的定制。

这里将一篇比较详细的blog粘贴过来。

http://mmmyddd.freeshell.net/wiki/android/overlay.html

The Android overlay mechanism allows the frameworkand package resources to be customized without changing the basepackages. The customizable resourses fall into the followingcategories.

• Configurations (string, bool, bool-array)
• Localization (string, string-array)
• UI Appearance (color, drawable, layout, style, theme,animation)
• Raw resources (audio, video, xml)

For detailed introduction on Android applicationresources, please refer to:

 http://developer.android.com/guide/topics/resources/available-resources.html

1 Add Overlay Directoriesfor Product

1.1 Product Overlays vsDevice Overlays

There are two types of overaly directories thataffect a product:

• PRODUCT_PACKAGE_OVERLAYS: used by a particularproduct
• DEVICE_PACKAGE_OVERLAYS: used several products that share acommon device model

The PRODUCT_PACKAGE_OVERLAYS will override theDEVICE_PACKAGE_OVERLAYS if they contain same resources, thebehavior is defined by:

build/core/package.mk (Line: 93)

LOCAL_RESOURCE_DIR := \  $(wildcard $(foreach dir, $(PRODUCT_PACKAGE_OVERLAYS), \    $(addprefix $(dir)/, $(LOCAL_RESOURCE_DIR)))) \  $(wildcard $(foreach dir, $(DEVICE_PACKAGE_OVERLAYS), \    $(addprefix $(dir)/, $(LOCAL_RESOURCE_DIR)))) \  $(LOCAL_RESOURCE_DIR)

1.2 Change the makefile to add overlays

To add an overlay directory to a product, changethe product configuration makefile (for example: device/vendor-name/device-name/product-name.mk) to add the followinglines:

PRODUCT_PACKAGE_OVERLAYS := device/vendor-name/device-name/product-name/overlay$(PRODUCT_PACKAGE_OVERLAYS)

Or:

DEVICE_PACKAGE_OVERLAYS := device/vendor-name/device-name/common/overlay$(DEVICE_PACKAGE_OVERLAYS)

 

If multiple overlay directories are required to beadded, separate them with blank charactors. The directories definedfirst in the line will override the following directories if theycontain the same set of resources.

 

1.3 Create resources underthe overlay directory

To overlay the resources in a base package, thesubdirectory containing the overlay resources under the overlaydirectory, must has the same path as the base package resourcedirectory relative to the Android project root.

For example, if we want to overlay the resourcesunder the base package directory:

packages/apps/Settings/res/

we need to create the directory:

/packages/apps/Settings/res/

and in the directory, put the overlay resources inthe files with the same path and file names as where they aredefined in the base package.

Note that:

• For color, bool, string, array, style/theme types, theresource values are identifed by their keys, so for these types,there is no need to put the resources in a file with the same nameas in the original base package.
• For layout, animation, picture drawables and raw types, theresources are indentifed by their file name, and overlay for theseresources should keep the file name same as in the basepackages.

2 Check the resource inAPK

After changed the overlay resources and built thetarget packages, sometimes we need to check if the overlaydirectory took effects and the values are changed in the finallygenerated apks.

2.2 Using AAPT

Usage: aapt l[ist] [-v] [-a] file.{zip,jar,apk}   List contents of Zip-compatible archive.  aapt d[ump] [--values] WHAT file.{apk} [asset [asset ...]]   badging          Print the label and icon for the app declared in APK.   permissions      Print the permissions from the APK.   resources        Print the resource table from the APK.   configurations   Print the configurations in the APK.   xmltree          Print the compiled xmls in the given assets.   xmlstrings       Print the strings of the given compiled xml assets.

Forexample:

1. To dumpstring, bool values:

aapt dump resources Settings.apk

2. To dumpa raw xml file:

aapt dump xmltree Settings.apk res/xml/appwidget_info.xml

3. To dump the current configurations/localizations:

aapt dump configurations Settings.apk

2.2 Usingapktools

Reference: http://code.google.com/p/android-apktool/

Apktool v1.5.0.5a056e3 - a tool for reengineering Android apk filesCopyright 2010 Ryszard Wi??niewski with smali v1.3.4-ibot8, and baksmali v1.3.4-ibot8Updated by iBotPeaches Apache License 2.0 (http://www.apache.org/licenses/LICENSE-2.0) Usage: apktool [-q|--quiet OR -v|--verbose] COMMAND [...] COMMANDs are:     d[ecode] [OPTS]  [        Decode  to          OPTS:         -s, --no-src            Do not decode sources.        -r, --no-res            Do not decode resources.        -d, --debug            Decode in debug mode. Check project page for more info.        -f, --force            Force delete destination directory.        -t , --frame-tag             Try to use framework files tagged by .        --keep-broken-res            Use if there was an error and some resources were dropped, e.g.:            "Invalid config flags detected. Dropping resources", but you            want to decode them anyway, even with errors. You will have to            fix them manually before building.     b[uild] [OPTS] [] []        Build an apk from already decoded application located in .         It will automatically detect, whether files was changed and perform        needed steps only.         If you omit  then current directory will be used.        If you omit  then /dist/        will be used.         OPTS:         -f, --force-all            Skip changes detection and build all files.        -d, --debug            Build in debug mode. Check project page for more info.     if|install-framework  []        Install framework file to your system. For additional info, see: https://github.com/iBotPeaches/brut.apktoolFor smali/baksmali info, see: http://code.google.com/p/smali/

2.3 Usingdumpres

 

 

3 More on AAPT andOverlay

3.1 How overlayworks

Whilebuilding the package APKs, the overlay directories are passed toaapt command lines using -S options in the same order as they are definedin 

PRODUCT_PACKAGE_OVERLAYS and DEVICE_PACKAGE_OVERLAYS.

Forexample, while building the Settings APK, the following command areexecuted:

out/host/linux-x86/bin/aapt package -u  -z \         -M packages/apps/Settings/AndroidManifest.xml \         -S device/vendor-name/device-name/product-name/overlay/packages/apps/Settings/res \         -S vendor/vendor-name/media/common/overlay/packages/apps/Settings/res -S packages/apps/Settings/res \         -I out/target/common/obj/APPS/framework-res_intermediates/package-export.apk \         --min-sdk-version 16 --target-sdk-version 16 --product default \         --version-code 16 --version-name 4.1.2-eng.xxxx.20121121.152327 \         -F out/target/product/product-name/obj/APPS/Settings_intermediates/package.apk

Note: some overlay directories that don't contain theSettings resources will be filtered first, and do not appear in theabove command line.

 

3.2 Add extra resources inOverlay

Though not recommanded, we can add new resources in overlaydirectory, for example, if base package Settings doesn't define a bool value with key no_such_key, wecan add it in the overlay file bool.xml likethis:

 true

Ifthe add-resource lineis missing, aapt toolwill complain while creating the apk file:

 

device/vendor-name/device-name/product-name/overlay/packages/apps/Settings/res/values/bools.xml:30:error: Resource at no_such_key appears in overlay but\
not in the base package; use toadd.

 

Another way to avoid the complaint is torun aapt with the option:

--auto-add-overlay    Automatically add resources that are only in overlays.