换肤，顾名思义，就是对应用中的视觉元素进行更新，呈现新的显示效果。一般来说，换肤的时候只是更新UI上使用的资源，如颜色，图片，字体等等。本文介绍一种笔者自己使用的基于布局的Android换肤方案，不仅可以更换所有的UI资源，而且可以更换主题样式（style）和布局样式。代码已托管到github：SkinFramework
换肤当然得有相应的皮肤包，不管是内置在应用内，还是做成可安装的皮肤应用包。但是这两种都有弊端：
1.内置在应用内会增加应用包的体积。
2.皮肤安装包需要安装过程，会占用更多的设备内置存储，用户会介意安装过多应用。而且为了是应用能够访问安装包内的资源，必须与应用使用相同的shareUserId。
鉴于此，本文推荐使用无需安装的外置皮肤包，优点在于：
1.无需安装，也无关乎shareUserId，不会引起用户反感。
2.按需下载使用，用户需要使用时自行下载，下载即可使用。
3.可放置于任何可访问的位置，SD卡或内置存储，可随时删除和添加，不会增加应用体积。
先来看一下效果图：
可以看到，图中有三种皮肤，默认皮肤，plain皮肤和vivid皮肤，都是更换了布局和资源的，其中还使用了AdapterView和Fragment作测试。可以看到，不同的皮肤有不同的布局样式，布局样式的不同也带来了很多可能，如隐藏或移动了功能入口。
所以说这是一个有很多可能的换肤框架，下面介绍一下核心 实现。
一、皮肤包
皮肤包就是一个不包含代码文件的Apk包，无需安装，可以新建工程，删除掉代码文件，复制应用里面需要修改的资源到新工程中修改，打成新包即可作为皮肤包使用，皮肤包后缀名可以改为任意。示例中使用了.skin作为后缀名。
二、皮肤包加载
皮肤包中包含的资源文件，需要加载到AssetManager中并创建Resources才能提供使用，关于Android的资源管理机制书上或网上已经有很多介绍，可以参考：Android中资源管理机制详细分析。所以我们的第一件事也是来加载皮肤包：
AssetManager assetManager = AssetManager.class.newInstance();
Method addAssetPath = assetManager.getClass().getMethod("addAssetPath", String.class);
//Return 0 on failure.
Object ret = addAssetPath.invoke(assetManager, skinPath);
if (Integer.parseInt(ret.toString()) == 0) {
throw new IllegalStateException("Add asset fail");
}
Resources localRes = context.getResources();
return new SkinResource(context, assetManager, localRes.getDisplayMetrics(), localRes.getConfiguration(), packageName);
三、资源管理器
加载了皮肤包，我们就有了两套可共使用的皮肤资源，应用默认资源和皮肤包资源，何时使用默认，何时使用皮肤，需要有一个管理器来决定，所以我们实现一个名为ComposedResources的类来扮演ResourcesManager：
/**
* Created by ARES on 2016/5/20
* This is a resources class consists of App default skin and external skin resources if exists. We will find resource in external skin resources first,then the default.
* Assume all resources ids are original so that we should find corresponding resources ids in skin .
*/ public class ComposedResources extends BaseResources {
static int LAYOUT_TAG_ID = -1;
private Context mContext;
private BaseSkinResources mSkinResources; public ComposedResources(Context context) {
this(context, null);
} public ComposedResources(Context context, BaseSkinResources skinResources) {
super(context.getResources());
mContext = context;
mSkinResources = skinResources;
} public ComposedResources setSkinResources(BaseSkinResources resources) {
mSkinResources = resources;
return this;
} public BaseSkinResources getSkinResources() {
return mSkinResources;
} @NonNull
@Override
public CharSequence getText(@StringRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
try {
return mSkinResources.getText(realId);
} catch (Exception e) {
}
}
return super.getText(id);
} @NonNull
@Override
public CharSequence getQuantityText(@PluralsRes int id, int quantity) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getQuantityText(realId, quantity);
}
return super.getQuantityText(id, quantity);
} @NonNull
@Override
public String getQuantityString(@PluralsRes int id, int quantity, Object... formatArgs) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getQuantityString(realId, quantity, formatArgs);
}
return super.getQuantityString(id, quantity, formatArgs);
} @NonNull
@Override
public String getQuantityString(@PluralsRes int id, int quantity) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getQuantityString(realId, quantity);
}
return super.getQuantityString(id, quantity);
} @Override
public CharSequence getText(@StringRes int id, CharSequence def) {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getText(realId, def);
}
return super.getText(id, def);
} @NonNull
@Override
public CharSequence[] getTextArray(@ArrayRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getTextArray(id);
}
return super.getTextArray(id);
} @NonNull
@Override
public String[] getStringArray(@ArrayRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getStringArray(realId);
}
return super.getStringArray(id);
} @NonNull
@Override
public int[] getIntArray(@ArrayRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getIntArray(realId);
}
return super.getIntArray(id);
} @NonNull
@Override
public TypedArray obtainTypedArray(@ArrayRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.obtainTypedArray(realId);
}
return super.obtainTypedArray(id);
} @Override
public float getDimension(@DimenRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getDimension(realId);
}
return super.getDimension(id);
} @Override
public int getDimensionPixelOffset(@DimenRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getDimensionPixelOffset(realId);
}
return super.getDimensionPixelOffset(id);
} @Override
public int getDimensionPixelSize(@DimenRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getDimensionPixelSize(realId);
}
return super.getDimensionPixelSize(id);
} @Override
public float getFraction(@FractionRes int id, int base, int pbase) {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getFraction(id, base, pbase);
}
return super.getFraction(id, base, pbase);
} @Override
public Drawable getDrawable(@DrawableRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getDrawable(realId);
}
return super.getDrawable(id);
} @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
@Override
public Drawable getDrawable(@DrawableRes int id, @Nullable Theme theme) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getDrawable(realId, theme);
}
return super.getDrawable(id, theme);
} @Override
public Drawable getDrawableForDensity(@DrawableRes int id, int density) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getDrawableForDensity(realId, density);
}
return super.getDrawableForDensity(id, density);
} @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
@Override
public Drawable getDrawableForDensity(@DrawableRes int id, int density, @Nullable Theme theme) {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getDrawableForDensity(realId, density, theme);
}
return super.getDrawableForDensity(id, density, theme);
} @Override
public Movie getMovie(@RawRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getMovie(realId);
}
return super.getMovie(id);
} @Override
public int getColor(@ColorRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getColor(realId);
}
return super.getColor(id);
} @RequiresApi(api = Build.VERSION_CODES.M)
@Override
public int getColor(@ColorRes int id, @Nullable Theme theme) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getColor(realId, theme);
}
return super.getColor(id, theme);
} @Nullable
@Override
public ColorStateList getColorStateList(@ColorRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getColorStateList(realId);
}
return super.getColorStateList(id);
} @RequiresApi(api = Build.VERSION_CODES.M)
@Nullable
@Override
public ColorStateList getColorStateList(@ColorRes int id, @Nullable Theme theme) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getColorStateList(realId, theme);
}
return super.getColorStateList(id, theme);
} @Override
public boolean getBoolean(@BoolRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getBoolean(realId);
}
return super.getBoolean(id);
} @Override
public int getInteger(@IntegerRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.getInteger(realId);
}
return super.getInteger(id);
} @Override
public XmlResourceParser getLayout(@LayoutRes int id) throws NotFoundException {
int realId = getCorrespondResIdStrictly(id);
if (realId > 0) {
return mSkinResources.getLayout(realId);
}
return super.getLayout(id);
} @Override
public XmlResourceParser getAnimation(@AnimRes int id) throws NotFoundException {
int realId = getCorrespondResIdStrictly(id);
if (realId > 0) {
return mSkinResources.getAnimation(realId);
}
return super.getAnimation(id);
} @Override
public XmlResourceParser getXml(@XmlRes int id) throws NotFoundException {
int realId = getCorrespondResIdStrictly(id);
if (realId > 0) {
return mSkinResources.getXml(realId);
}
return super.getXml(id);
} @Override
public InputStream openRawResource(@RawRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.openRawResource(realId);
}
return super.openRawResource(id);
} @Override
public InputStream openRawResource(@RawRes int id, TypedValue value) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.openRawResource(realId, value);
}
return super.openRawResource(id, value);
} @Override
public AssetFileDescriptor openRawResourceFd(@RawRes int id) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
return mSkinResources.openRawResourceFd(realId);
}
return super.openRawResourceFd(id);
} @Override
public void getValue(@AnyRes int id, TypedValue outValue, boolean resolveRefs) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
mSkinResources.getValue(realId, outValue, resolveRefs);
return;
}
super.getValue(id, outValue, resolveRefs);
} @Override
public void getValueForDensity(@AnyRes int id, int density, TypedValue outValue, boolean resolveRefs) throws NotFoundException {
int realId = getCorrespondResId(id);
if (realId > 0) {
mSkinResources.getValueForDensity(realId, density, outValue, resolveRefs);
return;
}
super.getValueForDensity(id, density, outValue, resolveRefs);
} @Override
public void getValue(String name, TypedValue outValue, boolean resolveRefs) throws NotFoundException {
if (mSkinResources != null) {
try {
mSkinResources.getValue(name, outValue, resolveRefs);
return;
} catch (Exception e) {
}
}
super.getValue(name, outValue, resolveRefs);
} @Override
public void updateConfiguration(Configuration config, DisplayMetrics metrics) {
if (mSkinResources != null) {
mSkinResources.updateConfiguration(config, metrics);
}
super.updateConfiguration(config, metrics);
} /**
* Get correspond resources id with app package. See also {@link #getCorrespondResId(int)}
*
* @param resId
* @return 0 if not exist
*/
public int getCorrespondResIdStrictly(int resId) {
if (mSkinResources == null) {
return 0;
}
String resName = getResourceName(resId);
return mSkinResources.getIdentifier(resName, null, null);
} /**
* Get correspond resources id with skin package. See also {@link #getCorrespondResId(int)}
*
* @param resId
* @return
*/
public int getCorrespondResId(int resId) {
if (mSkinResources == null) {
return 0;
}
return mSkinResources.getCorrespondResId(resId);
} @Override
public View getView(Context context, @LayoutRes int resId) {
//Take a resource id as the tag key.
if (LAYOUT_TAG_ID < 1) {
LAYOUT_TAG_ID = resId;
}
View view;
if (mSkinResources != null) {
int realId = getCorrespondResId(resId);
if (realId > 0) {
view = mSkinResources.getView(context, realId);
if (view != null) {
view.setTag(LAYOUT_TAG_ID, mSkinResources.getPackageName());
SkinUtils.showIds(view);
return view;
}
}
}
view = LayoutInflater.from(context).inflate(resId, null);
view.setTag(LAYOUT_TAG_ID, getPackageName());
SkinUtils.showIds(view);
return view;
} @Override
public String getPackageName() {
return mContext.getPackageName();
}
}
可以看到这个ResourceManager本身也是一个Resources，它继承自BaseResources，BaseResources继承自android.content.res.Resources。所以它可以直接作为应用的Resources来使用。其中有几点需要注意：
1.查找资源时，资源管理器应优先查找皮肤包中的资源，若皮肤包中没有相应资源，才使用应用默认资源。
2.每个应用包中的资源id是不同的，查找资源时，我们传入Resources的id都是应用中的id，而非皮肤包中的id，所以我们需要转换为皮肤包中相应的资源id，再获取具体的资源（此代码实现在SkinResources中，ComposedResources调用了此方法）：
/**
* Get correspond resource id in skin archive.
* @param resId Resource id in app.
* @return 0 if not exist
*/
public int getCorrespondResId(int resId) {
Resources appResources = getAppResources();
String resName = appResources.getResourceName(resId);
if (!TextUtils.isEmpty(resName)) {
String skinName = resName.replace(mAppPackageName, getPackageName());
int id = getIdentifier(skinName, null, null);
return id;
}
return 0;
}
3.在获取XmlResourceParser时，需要使用应用对于资源的描述，而非皮肤包中的资源描述，所以有了getCorrespondResIdStrictly：
/**
* Get correspond resources id with app package. See also {@link #getCorrespondResId(int)}
*
* @param resId
* @return 0 if not exist
*/
public int getCorrespondResIdStrictly(int resId) {
if (mSkinResources == null) {
return 0;
}
String resName = getResourceName(resId);
return mSkinResources.getIdentifier(resName, null, null);
}
4.我们使用了LAYOUT_TAG_ID来记录了Layout所属的皮肤包，以便可以动态的判断是否需要更换布局（此方法可以用在动态换肤的时候，详情参考Demo）：
@Override
public View getView(Context context, @LayoutRes int resId) {
//Take a resource id as the tag key.
if (LAYOUT_TAG_ID < 1) {
LAYOUT_TAG_ID = resId;
}
View view;
if (mSkinResources != null) {
int realId = getCorrespondResId(resId);
if (realId > 0) {
view = mSkinResources.getView(context, realId);
if (view != null) {
view.setTag(LAYOUT_TAG_ID, mSkinResources.getPackageName());
return view;
}
}
}
view = LayoutInflater.from(context).inflate(resId, null);
view.setTag(LAYOUT_TAG_ID, getPackageName());
return view;
}
四、布局更换处理
通过上述的代码，我们就已经能够完成常见资源的换肤了。但是对于布局资源，我们还需要做额外的处理。
1.Context与LayoutInflater
渲染View时，我们需要使用皮肤对应的Context和LayoutInflater，这样才能在View中使用正确的资源，所以我们为外置皮肤包创建相应的Context：
/**
* Context implementation for skin package.
*/
private class SkinThemeContext extends ContextThemeWrapper {
private WeakReference<Context> mContextRef; public SkinThemeContext(Context base) {
super();
if (base instanceof ContextThemeWrapper) {
attachBaseContext(((ContextThemeWrapper) base).getBaseContext());
mContextRef = new WeakReference<Context>(base);
} else {
attachBaseContext(base);
}
int themeRes = getThemeRes();
if (themeRes <= 0) {
themeRes = android.R.style.Theme_Light;
}
setTheme(themeRes);
} /**
* This implementation will support <code>onClick</code> attribute of view in xml.
* @param v
*/
public void onClick(View v) {
Context context = mContextRef == null ? null : mContextRef.get();
if (context == null) {
return;
}
if (context instanceof View.OnClickListener) {
((View.OnClickListener) context).onClick(v);
} else {
Class cls = context.getClass();
try {
Method m = cls.getDeclaredMethod("onClick", View.class);
if (m != null) {
m.invoke(context, v);
}
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
} @Override
public AssetManager getAssets() {
return getAssets();
} @Override
public Resources getResources() {
return SkinResource.this;
} private int getThemeRes() {
try {
Method m = Context.class.getMethod("getThemeResId");
return (int) m.invoke(getBaseContext());
} catch (Exception e) {
e.printStackTrace();
}
return -1;
} }
其中我们对xml布局文件中的onClick属性作了支持，同时通过提供了皮肤包对应的资源，然后我们使用这个Context的实例创建LayoutInflater并渲染View：
@Override
public View getView(Context context, @LayoutRes int resId) {
try {
Context skinContext = new SkinThemeContext(context);
View v = LayoutInflater.from(skinContext).inflate(resId, null);
handleView(skinContext, v);
return v;
} catch (Exception e) { }
return null;
}
其中注意到handleView方法，正如前文所说，每个应用包生成的资源id是不一样的，这里View中生成的id是皮肤包中的id，需要转换为应用中的id方可使用：
/**
* Handle view to support used by app.
*
* @param v View resource from skin package.
*/
public void handleView(Context context, View v) {
resetID();
//Id map: Key as skin id and Value as local id.
SparseIntArray array = new SparseIntArray();
buildIdRules(context, v, array);
int size = array.size();
// Map ids to which app can recognize locally.
for (int i = 0; i < size; i++) {
//Map id defined in skin package into real id in app.
v.findViewById(array.keyAt(i)).setId(array.valueAt(i));
}
} /**
* Extract id from view , build id rules and inflate rules if needed.
*
* @param v
* @param array
*/
protected void buildIdRules(Context context, View v, SparseIntArray array) {
if (v.getId() != View.NO_ID) {
//Get mapped id by id name.
String idName = getResourceEntryName(v.getId());
int mappedId = getAppResources().getIdentifier(idName, "id", context.getPackageName());
//Add custom id to avoid id conflict when mapped id not exist.
//Key as skin id and value as mapped id.
array.put(v.getId(), mappedId > 0 ? mappedId : generateId());
}
if (v instanceof ViewGroup) {
ViewGroup vp = (ViewGroup) v;
int childCount = vp.getChildCount();
for (int i = 0; i < childCount; i++) {
buildIdRules(context, vp.getChildAt(i), array);
}
}
buildInflateRules(v, array);
} /**
* Build inflate rules.
*
* @param v
* @param array ID map of which Key as skin id and value as mapped id.
*/
protected void buildInflateRules(View v, SparseIntArray array) {
ViewGroup.LayoutParams lp = v.getLayoutParams();
if (lp == null) {
return;
}
if (lp instanceof RelativeLayout.LayoutParams) {
int[] rules = ((RelativeLayout.LayoutParams) lp).getRules();
if (rules == null) {
return;
}
int size = rules.length;
int mapRule = -1;
for (int i = 0; i < size; i++) {
//Key as skin id and value as mapped id.
if (rules[i] > 0 && (mapRule = array.get(rules[i])) > 0) {
// Log.i(TAG, "Rules[" + i + "]: Mapped from: " + rules[i] + " to " +mapRule);
rules[i] = mapRule;
}
}
}
}
五、使用
下载源码，集成skin module到工程中，然后使用SkinManager提供的接口：
public SkinManager initialize(Context context);//初始化皮肤管理器 /**
* Register an observer to be informed of skin changed for ui interface such as activity,fragment, dialog etc.
* @param observer
*/
public void register(ISkinObserver observer)；//注册换肤监听器，用于需要动态换肤的场景。 /**
* Get resources.
* @return
*/
public BaseResources getResources()；//获取资源 /**
* Change skin.
* @param skinPath Path of skin archive.
* @param pkgName Package name of skin archive.
* @param cb Callback to be informed of skin-changing event.
*/
public void changeSkin(String skinPath, String pkgName, ISkinCallback cb)；//更换皮肤 /**
* Restore skin to app default skin.
*
* @param cb
*/
public void restoreSkin(ISkinCallback cb) ；//恢复应用默认皮肤 /**
* Resume skin.Call it on application started.
*
* @param cb
*/
public void resumeSkin(ISkinCallback cb) ；//恢复当前使用的皮肤，应在应用启动界面调用。
框架支持两种换肤方式：
1.静态换肤（推荐）
换肤完成后，关闭掉所有的Activity，然后重新启动主界面。简单方便。
2.动态换肤
需要换肤的Activity、Fragment、Dialog实现ISkinObserver, 并通过register(ISkinObserver observer)注册到SkinManager,动态更换布局，详情见Sample代码。
这种方式需要重新渲染View，绑定数据，在使用Fragment时，还需要在换肤期间detach/attach fragment,使用起来比较麻烦。优点是换肤后可以停留在原来界面。
两种方式都需要使用SkinManager提供的Resource来获取布局或其他资源。推荐写自己的BaseActivity，重写getResources()返回SkinManager提供的Resources方便使用。小伙伴们根据自己的实际情况来选择具体使用何种方式。
好了，到这里换肤框架就介绍完了，欢迎关注SkinFramework的最新动态，若有任何建议和意见，欢迎指出！