实现Android插件化的核心技术简介(二):Android dynamic load resources
2016-07-23 23:34
597 查看
实现Android插件化的核心技术(二):Android dynamic load resources
Android resources are loaded by AssetManager.
安卓资源由AssetManager加载。
While android application launched, it creates an
By default, it adds:
应用启动时,系统会为其创建一个
"/framework/base.apk" - Android base resources (base)
"/data/app/*.apk" - The launching apk resources (host)
As we know, android resources are accessed by an unique index with format 0xPPTTNNNN.
所有的资源需要通过一个唯一的id来访问
PP - the resource package id (00-02: system, 7f: application, 03-7e: reserved)
TT - the resource type id (types are 'attr', 'layout', 'string' and etc.)
NNNN - the resource entry id
To avoid id conflicts, the resources ids in host and plugins should be partitioned.
为避免id冲突,宿主以及各个插件之间的资源id需要分段处理。
There are some ways to do this:
Create a self-contained asset manager for each plugin.
❌Plugins can not access resource to each other.
Add all plugins' asset path to host's asset manager.
Arrange the entry ids (NNNN) by public.xml
⚠️ High cost of maintenance.
Arrange the type ids (TT) by public.xml
❌Plugins can not access resource to each other.
Arrange the package ids (PP)
Modify aapt source code
⚠️ High cost of maintenance.
Modify the products of aapt (binary resources.arsc and *.xml)
✅Seamless, and the ability of ultimate slicing.
Now, out final plan is to repack android asset package and reset package id of it's resources.
我们的最终方案是对资源包进行重新打包,重设资源id
First of all, unzip the package file resources.ap_, get files:
首先,解压resources.ap_文件,可以得到:
They are all binary files, data structs are in ResourcesType.h
这些文件都是二进制的,数据结构参见ResourcesType.h
Repack resources.arsc
Reset package id
Filter types
Dynamic package reference
In Android 5.0+ needs to set the dynamicRefTable for lookup bag parent.
5.0以上需要对二进制文件加入“资源包id映射”数据段,以使得能正确查找到主题等bag的parent。
What's the bag and bag parent?
For example, we made a plugin with package id 0x34, and defined themes in it's styles.xml:
And then after aapt executed, we got a bag tree as following: (run aapt d --values resources *.apk to see more)
The AppTheme.NoActionBar's parent is AppTheme, but in ResourcesType.cpp,
If has not pre-define dynamicRefTable (declare what 0x34 is), while looking up the parent ofAppTheme.NoActionBar (0x34050000) it would abort and never find AppTheme andTheme.AppCompat.Light.DarkActionBar.
The result is that, if your activity is an instance of AppCompatActivity but cannot apply theAppCompat Theme, then a crash raised. Let's see the codes:
Repack *.xml
Android resources are loaded by AssetManager.
安卓资源由AssetManager加载。
While android application launched, it creates an
AssetManagerinstance and add resources search paths by
addAssetPath.
By default, it adds:
应用启动时,系统会为其创建一个
AssetManager实例,并由
addAssetPath方法添加资源搜索路径,默认添加:
"/framework/base.apk" - Android base resources (base)
"/data/app/*.apk" - The launching apk resources (host)
As we know, android resources are accessed by an unique index with format 0xPPTTNNNN.
所有的资源需要通过一个唯一的id来访问
PP - the resource package id (00-02: system, 7f: application, 03-7e: reserved)
TT - the resource type id (types are 'attr', 'layout', 'string' and etc.)
NNNN - the resource entry id
To avoid id conflicts, the resources ids in host and plugins should be partitioned.
为避免id冲突,宿主以及各个插件之间的资源id需要分段处理。
There are some ways to do this:
Create a self-contained asset manager for each plugin.
插件独立使用一个资源管理器
❌Plugins can not access resource to each other.
插件间无法访问资源
Add all plugins' asset path to host's asset manager.
添加所有资源路径到宿主
Arrange the entry ids (NNNN) by public.xml
分配NN段
⚠️ High cost of maintenance.
字段有限,不好维护
Arrange the type ids (TT) by public.xml
分配TT段
❌Plugins can not access resource to each other.
插件间无法访问资源
Arrange the package ids (PP)
分配PP段
Modify aapt source code
修改aapt源码
⚠️ High cost of maintenance.
不好维护
Modify the products of aapt (binary resources.arsc and *.xml)
修改aapt生成产物
✅Seamless, and the ability of ultimate slicing.
无缝连接,支持极致剪裁
Now, out final plan is to repack android asset package and reset package id of it's resources.
我们的最终方案是对资源包进行重新打包,重设资源id
Repack android asset package
First of all, unzip the package file resources.ap_, get files:首先,解压resources.ap_文件,可以得到:
AndroidManifest.xml resources.arsc res `-- layout `-- activity_main.xml
They are all binary files, data structs are in ResourcesType.h
这些文件都是二进制的,数据结构参见ResourcesType.h
Repack resources.arsc
chunk | type | note |
---|---|---|
Table header | RES_TABLE_TYPE = 0x002 | |
Resource strings | RES_STRING_POOL_TYPE = 0x001 | e.g. 'Hello World!' |
Package header | RES_TABLE_PACKAGE_TYPE = 0x200 | Rewrite entry: package id |
Type strings | RES_STRING_POOL_TYPE = 0x001 | e.g. 'attr', 'layout', etc. |
Key strings | RES_STRING_POOL_TYPE = 0x001 | e.g. 'activity_main', etc. |
DynamicRefTable | RES_TABLE_LIBRARY_TYPE = 0x0203 | Insert entry for Android 5.0+ |
Type spec | RES_TABLE_TYPE_SPEC_TYPE = 0x0202 | |
Type info | RES_TABLE_TYPE_TYPE = 0x0201 | Rewrite entry: resource entry value |
Filter types
Dynamic package reference
In Android 5.0+ needs to set the dynamicRefTable for lookup bag parent.
5.0以上需要对二进制文件加入“资源包id映射”数据段,以使得能正确查找到主题等bag的parent。
What's the bag and bag parent?
For example, we made a plugin with package id 0x34, and defined themes in it's styles.xml:
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">..</style> <style name="AppTheme.NoActionBar">..</style>
And then after aapt executed, we got a bag tree as following: (run aapt d --values resources *.apk to see more)
Theme.AppCompat.Light.DarkActionBar `-- AppTheme <bag> (id: 0x34050001) `-- AppTheme.NoActionBar <bag> (id: 0x34050000)
The AppTheme.NoActionBar's parent is AppTheme, but in ResourcesType.cpp,
If has not pre-define dynamicRefTable (declare what 0x34 is), while looking up the parent ofAppTheme.NoActionBar (0x34050000) it would abort and never find AppTheme andTheme.AppCompat.Light.DarkActionBar.
The result is that, if your activity is an instance of AppCompatActivity but cannot apply theAppCompat Theme, then a crash raised. Let's see the codes:
ssize_t ResTable::getBagLocked(uint32_t resID, const bag_entry** outBag, uint32_t* outTypeSpecFlags) const { ... bag_entry* cur = entries+curEntry; cur->stringBlock = entry.package->header->index; cur->map.name.ident = newName; cur->map.value.copyFrom_dtoh(map->value); status_t err = grp->dynamicRefTable.lookupResourceValue(&cur->map.value); if (err != NO_ERROR) { ALOGE("Reference item(0x%08x) in bag could not be resolved.", cur->map.value.data); return UNKNOWN_ERROR; } ... }
status_t DynamicRefTable::lookupResourceValue(Res_value* value) const { ... status_t err = lookupResourceId(&value->data); if (err != NO_ERROR) { return err; } ... }
status_t DynamicRefTable::lookupResourceId(uint32_t* resId) const { uint32_t res = *resId; size_t packageId = Res_GETPACKAGE(res) + 1; if (packageId == APP_PACKAGE_ID) { // No lookup needs to be done, app package IDs are absolute. return NO_ERROR; } if (packageId == 0) { // The package ID is 0x00. That means that a shared library is accessing // its own local resource, so we fix up the resource with the calling // package ID. *resId |= ((uint32_t) mAssignedPackageId) << 24; return NO_ERROR; } // Do a proper lookup. uint8_t translatedId = mLookupTable[packageId]; if (translatedId == 0) { //-------------------------------------------------------- // Lookup Code Block // [0x03, 0x7e] goes here //-------------------------------------------------------- ALOGV("DynamicRefTable(0x%02x): No mapping for build-time package ID 0x%02x.", (uint8_t)mAssignedPackageId, (uint8_t)packageId); for (size_t i = 0; i < 256; i++) { if (mLookupTable[i] != 0) { ALOGV("e[0x%02x] -> 0x%02x", (uint8_t)i, mLookupTable[i]); } } return UNKNOWN_ERROR; } *resId = (res & 0x00ffffff) | (((uint32_t) translatedId) << 24); return NO_ERROR; }
Repack *.xml
chunk | type | note |
---|---|---|
Xml header | RES_XML_TYPE = 0x0003 | |
Attr ids | RES_XML_RESOURCE_MAP_TYPE = 0x180 | Rewrite entry: each attr id |
Xml node | RES_XML_START_ELEMENT_TYPE = 0x102 | Rewrite entry: node attribute value |
相关文章推荐
- 实现Android插件化的核心技术简介(一):Android dynamic load classes
- 深入Android MediaPlayer的使用方法详解
- Android插件化(使用Small框架)
- Android 圆形ImageView
- Android广播
- Android应用程序内部切换语言及自定义语言
- Android ListView几种Adapter用法简介
- 四大组件之Activity
- Android Notification 的总结分析
- 利用Netbean开发Android应用程序注意事项
- 【Java源码分析】Android-SparseArray源码分析
- Android照片墙-多图加载
- 【Java源码分析】Android-LruCache源码分析
- Android的消息机制
- Android 中 Canvas 绘图之 PorterDuffXfermode 使用及工作原理详解
- 2016这些Android技术可能会很火
- Android TV中获取有线网卡的MAC地址
- Android Binder设计与实现 - 设计篇
- android垃圾回收机制及程序优化System.gc
- Android -- json数据格式解析练习