Android可更换布局的换肤方案

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！