app 换肤

本文最后更新于:2 年前

Reference


需求

  1. 替换 res 目录中的资源;
  2. 不重启;
  3. 无闪烁。

换肤原理

1、设置 Activity 的 LayoutInflater 为自定义的 Factory2,这样当调用 Activity#setContentView() 方法时会接管创建 View 的操作;
2、在创建 View 成功后,查看 View 是否包含在换肤范围内的属性,如果有,就将 View 存起来;
3、当执行换肤时,会先下载皮肤包,然后将皮肤包中的资源合并到宿主 app 的资源中,形成新的资源包;遍历(2)中保存的 View,将资源替换为新的资源包中的资源。

源码:skin_demo


资源

分类

assets

res

  • animator:属性动画 XML 文件
  • anim:视图动画 XML 文件
  • color:颜色 XML 文件
  • drawable:drawable XML 文件、Bitmap 文件(.png、.9.png、.jpg、.gif 等)
  • layout:布局 XML 文件
  • menu:菜单 XML 文件
  • raw:原始资源文件
  • values:字符串、颜色、尺寸、样式、属性等 XML 文件
  • xml:XML 文件

资源打包流程

资源打包是由 AAPT 工具完成,assert、res/raw、Bitmap 文件会被原封不动地打包到 APK 里,XML 会被编译成二进制文件,最终生成 R.java 和 resources.arsc。

详细流程:

R.java 存储资源 ID(系统资源以 0x01 开头,应用资源以 0x7f 开头):

resources.arsc 存储资源 ID 和文件的映射关系:

布局 XML 解析流程

在 Activity 中加载布局 XML 文件

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public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}

Activity:直接交给 Window 处理

此处的 Window 是 PhoneWindow。

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public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
...
}

PhoneWindow:创建 DecorView

创建 DecorView 作为 Window 的顶层 View,然后交给 LayoutInflater 处理,同时 DecorView 作为 parent。

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public void setContentView(int layoutResID) {
if (mContentParent == null) {
installDecor();
}
...
mLayoutInflater.inflate(layoutResID, mContentParent);
...
}

LayoutInflater 处理

1、获取 Context 绑定的 Resources;
2、创建 XML 资源解析器,解析 XML;
3、通过 createViewFromTag() 方法创建 View。

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public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
final Resources res = getContext().getResources();
final XmlResourceParser parser = res.getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
...
View result = root;
...
final String name = parser.getName();
...
final View temp = createViewFromTag(root, name, inflaterContext, attrs);

ViewGroup.LayoutParams params = null;

if (root != null) {
params = root.generateLayoutParams(attrs);
if (!attachToRoot) {
temp.setLayoutParams(params);
}
}

rInflateChildren(parser, temp, attrs, true);

if (root != null && attachToRoot) {
root.addView(temp, params);
}

if (root == null || !attachToRoot) {
result = temp;
}

return result;
}

View createViewFromTag(View parent, String name, Context context, AttributeSet attrs, boolean ignoreThemeAttr) {
...
View view;
// view 创建顺序是 mFactory2、mFactory、mPrivateFactory、onCreateView、createView
if (mFactory2 != null) {
view = mFactory2.onCreateView(parent, name, context, attrs);
} else if (mFactory != null) {
view = mFactory.onCreateView(name, context, attrs);
} else {
view = null;
}

if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, context, attrs);
}

if (view == null) {
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
if (-1 == name.indexOf('.')) {
view = onCreateView(parent, name, attrs);
} else {
view = createView(name, null, attrs);
}
} finally {
mConstructorArgs[0] = lastContext;
}
}

return view;
}

所以自定义 Factory2 就可以实现抢在系统之前创建 View。

Resources 初始化流程

在 app 启动流程中,当 zygote fork 出 app 进程后,会在 app 进程执行 ActivityThread#main() 方法。

ActivityThread:除了启动主线程 Looper,还创建了 ContextImpl 对象

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public static void main(String[] args) {
...

Looper.prepareMainLooper();

...

ActivityThread thread = new ActivityThread();
thread.attach(false, startSeq);

if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}

...

Looper.loop();
}

private void attach(boolean system, long startSeq) {
sCurrentActivityThread = this;
mSystemThread = system;

...

mInstrumentation = new Instrumentation();
mInstrumentation.basicInit(this);
ContextImpl context = ContextImpl.createAppContext(this, getSystemContext().mPackageInfo);
mInitialApplication = context.mPackageInfo.makeApplication(true, null);
mInitialApplication.onCreate();

...
}

ContextImpl:通过 LoadedApk 获取 Resources,并绑定

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static ContextImpl createAppContext(ActivityThread mainThread, LoadedApk packageInfo) {
...

ContextImpl context = new ContextImpl(null, mainThread, packageInfo, null, null, null, 0, null);
context.setResources(packageInfo.getResources());
return context;
}

LoadedApk:将获取 Resources 的工作转给 ResourcesManager

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public Resources getResources() {
if (mResources == null) {
final String[] splitPaths;
try {
splitPaths = getSplitPaths(null);
} catch (NameNotFoundException e) {
throw new AssertionError("null split not found");
}

mResources = ResourcesManager.getInstance().getResources(null, mResDir, splitPaths, mOverlayDirs, mApplicationInfo.sharedLibraryFiles, Display.DEFAULT_DISPLAY, null, getCompatibilityInfo(), getClassLoader());
}
return mResources;
}

ResourcesManager:创建 ResourcesImpl 中的 AssetManager;创建 ResourcesImpl

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public @Nullable Resources getResources(@Nullable IBinder activityToken, @Nullable String resDir, @Nullable String[] splitResDirs, @Nullable String[] overlayDirs, @Nullable String[] libDirs, int displayId, @Nullable Configuration overrideConfig, @NonNull CompatibilityInfo compatInfo, @Nullable ClassLoader classLoader) {
final ResourcesKey key = new ResourcesKey(resDir, splitResDirs, overlayDirs, libDirs, displayId, overrideConfig != null ? new Configuration(overrideConfig) : null, compatInfo);
classLoader = classLoader != null ? classLoader : ClassLoader.getSystemClassLoader();
return getOrCreateResources(activityToken, key, classLoader);
}

private @Nullable Resources getOrCreateResources(@Nullable IBinder activityToken, @NonNull ResourcesKey key, @NonNull ClassLoader classLoader) {
...

ResourcesImpl resourcesImpl = createResourcesImpl(key);
if (resourcesImpl == null) {
return null;
}

...

final Resources resources;
if (activityToken != null) {
resources = getOrCreateResourcesForActivityLocked(activityToken, classLoader, resourcesImpl, key.mCompatInfo);
} else {
resources = getOrCreateResourcesLocked(classLoader, resourcesImpl, key.mCompatInfo);
}
return resources;
}

private @Nullable ResourcesImpl createResourcesImpl(@NonNull ResourcesKey key) {
final DisplayAdjustments daj = new DisplayAdjustments(key.mOverrideConfiguration);
daj.setCompatibilityInfo(key.mCompatInfo);

final AssetManager assets = createAssetManager(key);
if (assets == null) {
return null;
}

final DisplayMetrics dm = getDisplayMetrics(key.mDisplayId, daj);
final Configuration config = generateConfig(key, dm);
final ResourcesImpl impl = new ResourcesImpl(assets, dm, config, daj);
return impl;
}

@VisibleForTesting
protected @Nullable AssetManager createAssetManager(@NonNull final ResourcesKey key) {
final AssetManager.Builder builder = new AssetManager.Builder();

if (key.mResDir != null) {
try {
builder.addApkAssets(loadApkAssets(key.mResDir, false /*sharedLib*/, false /*overlay*/));
} catch (IOException e) {
Log.e(TAG, "failed to add asset path " + key.mResDir);
return null;
}
}

if (key.mSplitResDirs != null) {
for (final String splitResDir : key.mSplitResDirs) {
try {
builder.addApkAssets(loadApkAssets(splitResDir, false /*sharedLib*/, false /*overlay*/));
} catch (IOException e) {
Log.e(TAG, "failed to add split asset path " + splitResDir);
return null;
}
}
}

if (key.mOverlayDirs != null) {
for (final String idmapPath : key.mOverlayDirs) {
try {
builder.addApkAssets(loadApkAssets(idmapPath, false /*sharedLib*/, true /*overlay*/));
} catch (IOException e) {
Log.w(TAG, "failed to add overlay path " + idmapPath);
}
}
}

if (key.mLibDirs != null) {
for (final String libDir : key.mLibDirs) {
if (libDir.endsWith(".apk")) {
try {
builder.addApkAssets(loadApkAssets(libDir, true /*sharedLib*/, false /*overlay*/));
} catch (IOException e) {
Log.w(TAG, "Asset path '" + libDir +
"' does not exist or contains no resources.");
}
}
}
}

return builder.build();
}

AssetManager:将系统资源和用户资源合并

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public static class Builder {
private ArrayList<ApkAssets> mUserApkAssets = new ArrayList<>();

public Builder addApkAssets(ApkAssets apkAssets) {
mUserApkAssets.add(apkAssets);
return this;
}

public AssetManager build() {
final ApkAssets[] systemApkAssets = getSystem().getApkAssets();

final int totalApkAssetCount = systemApkAssets.length + mUserApkAssets.size();
final ApkAssets[] apkAssets = new ApkAssets[totalApkAssetCount];

System.arraycopy(systemApkAssets, 0, apkAssets, 0, systemApkAssets.length);

final int userApkAssetCount = mUserApkAssets.size();
for (int i = 0; i < userApkAssetCount; i++) {
apkAssets[i + systemApkAssets.length] = mUserApkAssets.get(i);
}

final AssetManager assetManager = new AssetManager(false /*sentinel*/);
assetManager.mApkAssets = apkAssets;
AssetManager.nativeSetApkAssets(assetManager.mObject, apkAssets, false /*invalidateCaches*/);
return assetManager;
}
}

资源查找流程

以查找字符串为例,依次经过 Context -> ContextImpl-> Resources -> ResourcesImpl -> AssetManager,其中 ContextImpl、ResourcesImpl、AssetManager 在 app 启动时初始化 Resource 时创建。
AssetManager 调用 native 层代码会获取 ResTable 资源表,然后根据机器配置在 ResTable 的 mPackageGroups 数组中查找到一个最合适的值。详细流程参考Android资源查找分析

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getString(R.string.app_name);

Context

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@NonNull
public final String getString(@StringRes int resId) {
return getResources().getString(resId);
}

ContextImpl

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@Override
public Resources getResources() {
return mResources;
}

Resources

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@NonNull
public String getString(@StringRes int id) throws NotFoundException {
return getText(id).toString();
}

@NonNull public CharSequence getText(@StringRes int id) throws NotFoundException {
CharSequence res = mResourcesImpl.getAssets().getResourceText(id);
if (res != null) {
return res;
}
throw new NotFoundException("String resource ID #0x" + Integer.toHexString(id));
}

ResourcesImpl

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@UnsupportedAppUsage
public AssetManager getAssets() {
return mAssets;
}

AssetManager

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@Nullable CharSequence getResourceText(@StringRes int resId) {
synchronized (this) {
final TypedValue outValue = mValue;
if (getResourceValue(resId, 0, outValue, true)) {
return outValue.coerceToString();
}
return null;
}
}

boolean getResourceValue(@AnyRes int resId, int densityDpi, @NonNull TypedValue outValue, boolean resolveRefs) {
Preconditions.checkNotNull(outValue, "outValue");
synchronized (this) {
ensureValidLocked();
final int cookie = nativeGetResourceValue(mObject, resId, (short) densityDpi, outValue, resolveRefs);
if (cookie <= 0) {
return false;
}

outValue.changingConfigurations = ActivityInfo.activityInfoConfigNativeToJava(outValue.changingConfigurations);

if (outValue.type == TypedValue.TYPE_STRING) {
outValue.string = mApkAssets[cookie - 1].getStringFromPool(outValue.data);
}
return true;
}
}

效果



app 换肤
https://weichao.io/98e10d6f6955/
作者
魏超
发布于
2020年8月13日
更新于
2020年8月13日
许可协议