Android 两行代码实现换肤从appcompat-v7原理出发

背景

换肤方案原理在网上已经很多了, 这里不再详细描述, 强迫症的我总是想让提供给别人使用的SDK尽量好用, 哪怕是给自己带来额外的工作量, 经过一段时间的奋斗, 实现了一个自我感觉良好的换肤框架.

这里主要来看看Android 源码中”com.android.support:appcompat-v7”包的实现, 以及源码思想在Android-skin-support中的应用 – 如何打造一款好用的换肤框架.

appcompat-v7包实现

首先来看一下源码的实现:
AppCompatActivity源码

public class AppCompatActivity extends FragmentActivity {@Overrideprotected void onCreate(@Nullable Bundle savedInstanceState) {final AppCompatDelegate delegate = getDelegate();delegate.installViewFactory();delegate.onCreate(savedInstanceState);...}@Overridepublic MenuInflater getMenuInflater() {return getDelegate().getMenuInflater();}@Overridepublic void setContentView(@LayoutRes int layoutResID) {getDelegate().setContentView(layoutResID);}@Overridepublic void setContentView(View view) {getDelegate().setContentView(view);}....
}

AppCompatActivity 将大部分生命周期委托给了AppCompatDelegate

再看看相关的类图

AppCompateDelegate的子类AppCompatDelegateImplV9

class AppCompatDelegateImplV9 extends AppCompatDelegateImplBaseimplements MenuBuilder.Callback, LayoutInflaterFactory {@Overridepublic void installViewFactory() {LayoutInflater layoutInflater = LayoutInflater.from(mContext);if (layoutInflater.getFactory() == null) {LayoutInflaterCompat.setFactory(layoutInflater, this);} else {if (!(LayoutInflaterCompat.getFactory(layoutInflater)instanceof AppCompatDelegateImplV9)) {Log.i(TAG, "The Activity's LayoutInflater already has a Factory installed"+ " so we can not install AppCompat's");}}}
}

从这可以看出通过实现LayoutInflaterFactory接口来实现换肤至少可以支持到api 9以上

网上很多换肤框架的实现, 通过LayoutInflater.setFactory的方式, 在回调的onCreateView中解析每一个View的attrs, 判断是否有已标记需要换肤的属性, 比方说background, textColor, 或者说相应资源是否为skin_开头等等.
然后保存到map中, 对每一个View做for循环去遍历所有的attr, 想要对更多的属性进行换肤, 需要Activity实现接口, 将需要换肤的View, 以及相应的属性收集到一起
那么是不是能够寻求一种让使用者更方便的方式来实现, 做一个侵入性尽量小的框架呢?

本着开发者应有的好奇心, 深入的研究了一些v7包的实现

AppCompatDelegateImplV9中, 在LayoutInflaterFactory的接口方法onCreateView 中将View的创建交给了AppCompatViewInflater

@Override
public final View onCreateView(View parent, String name,Context context, AttributeSet attrs) {// First let the Activity's Factory try and inflate the viewfinal View view = callActivityOnCreateView(parent, name, context, attrs);if (view != null) {return view;}// If the Factory didn't handle it, let our createView() method tryreturn createView(parent, name, context, attrs);
}@Override
public View createView(View parent, final String name, @NonNull Context context,@NonNull AttributeSet attrs) {final boolean isPre21 = Build.VERSION.SDK_INT < 21;if (mAppCompatViewInflater == null) {mAppCompatViewInflater = new AppCompatViewInflater();}// We only want the View to inherit its context if we're running pre-v21final boolean inheritContext = isPre21 && shouldInheritContext((ViewParent) parent);return mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext,isPre21, /* Only read android:theme pre-L (L+ handles this anyway) */true, /* Read read app:theme as a fallback at all times for legacy reasons */VectorEnabledTintResources.shouldBeUsed() /* Only tint wrap the context if enabled */);
}

再来看一下AppCompatViewInflater中createView的实现

public final View createView(View parent, final String name, @NonNull Context context,@NonNull AttributeSet attrs, boolean inheritContext,boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {......View view = null;switch (name) {case "TextView":view = new AppCompatTextView(context, attrs);break;case "ImageView":view = new AppCompatImageView(context, attrs);break;case "Button":view = new AppCompatButton(context, attrs);break;case "EditText":view = new AppCompatEditText(context, attrs);break;case "Spinner":view = new AppCompatSpinner(context, attrs);break;case "ImageButton":view = new AppCompatImageButton(context, attrs);break;case "CheckBox":view = new AppCompatCheckBox(context, attrs);break;......}......return view;
}

再看一下其中一个类AppCompatTextView的实现

public class AppCompatTextView extends TextView implements TintableBackgroundView {public AppCompatTextView(Context context, AttributeSet attrs, int defStyleAttr) {super(TintContextWrapper.wrap(context), attrs, defStyleAttr);mBackgroundTintHelper = new AppCompatBackgroundHelper(this);mBackgroundTintHelper.loadFromAttributes(attrs, defStyleAttr);mTextHelper = AppCompatTextHelper.create(this);mTextHelper.loadFromAttributes(attrs, defStyleAttr);mTextHelper.applyCompoundDrawablesTints();}@Overridepublic void setBackgroundResource(@DrawableRes int resId) {super.setBackgroundResource(resId);if (mBackgroundTintHelper != null) {mBackgroundTintHelper.onSetBackgroundResource(resId);}}......
}

AppCompatBackgroundHelper.Java

void loadFromAttributes(AttributeSet attrs, int defStyleAttr) {TintTypedArray a = TintTypedArray.obtainStyledAttributes(mView.getContext(), attrs,R.styleable.ViewBackgroundHelper, defStyleAttr, 0);......if (a.hasValue(R.styleable.ViewBackgroundHelper_android_background)) {mBackgroundResId = a.getResourceId(R.styleable.ViewBackgroundHelper_android_background, -1);ColorStateList tint = mDrawableManager.getTintList(mView.getContext(), mBackgroundResId);if (tint != null) {setInternalBackgroundTint(tint);}}......
}

到这里我仿佛是发现了新大陆一样兴奋, 源码中可以通过拦截View创建过程, 替换一些基础的组件, 然后对一些特殊的属性(eg: background, textColor) 做处理, 那我们为什么不能将这种思想拿到换肤框架中来使用呢?

Android-skin-support换肤框架实现

抱着试一试不会少块肉的心情, 开始了我的换肤框架开发之路

先简单讲一下原理:
1. 参照源码实现在Activity onCreate中为LayoutInflater setFactory, 将View的创建过程交给自定义的SkinCompatViewInflater类来实现
2. 重写系统组件, 实现换肤接口, 表明该控件支持换肤, 并在View创建之后统一收集
3. 在重写的View中解析出需要换肤的属性, 并保存ResId到成员变量
4. 重写类似setBackgroundResource方法, 解析需要换肤的属性, 并保存变量
5. applySkin 在切换皮肤的时候, 从皮肤资源中获取资源

下面说一个简单的例子(SkinCompatTextView):
1. 实现SkinCompatSupportable接口
2. 在构造方法中通过SkinCompatBackgroundHelper和SkinCompatTextHelper分别解析出background, textColor并保存
3. 重写setBackgroundResource和setTextAppearance, 解析出对应的资源Id, 表明该控件支持从代码中设置资源, 且支持该资源换肤
4. 在用户点击切换皮肤时调用applySkin方法设置皮肤

public interface SkinCompatSupportable {void applySkin();
}public class SkinCompatTextView extends AppCompatTextView implements SkinCompatSupportable {public SkinCompatTextView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);mBackgroundTintHelper = new SkinCompatBackgroundHelper(this);mBackgroundTintHelper.loadFromAttributes(attrs, defStyleAttr);mTextHelper = new SkinCompatTextHelper(this);mTextHelper.loadFromAttributes(attrs, defStyleAttr);}@Overridepublic void setBackgroundResource(@DrawableRes int resId) {super.setBackgroundResource(resId);if (mBackgroundTintHelper != null) {mBackgroundTintHelper.onSetBackgroundResource(resId);}}@Overridepublic void setTextAppearance(Context context, int resId) {super.setTextAppearance(context, resId);if (mTextHelper != null) {mTextHelper.onSetTextAppearance(context, resId);}}@Overridepublic void applySkin() {if (mBackgroundTintHelper != null) {mBackgroundTintHelper.applySkin();}if (mTextHelper != null) {mTextHelper.applySkin();}}
}public class SkinCompatTextHelper extends SkinCompatHelper {private static final String TAG = SkinCompatTextHelper.class.getSimpleName();private final TextView mView;private int mTextColorResId = INVALID_ID;private int mTextColorHintResId = INVALID_ID;public SkinCompatTextHelper(TextView view) {mView = view;}public void loadFromAttributes(AttributeSet attrs, int defStyleAttr) {final Context context = mView.getContext();// First read the TextAppearance style idTintTypedArray a = TintTypedArray.obtainStyledAttributes(context, attrs,R.styleable.SkinCompatTextHelper, defStyleAttr, 0);final int ap = a.getResourceId(R.styleable.SkinCompatTextHelper_android_textAppearance, INVALID_ID);SkinLog.d(TAG, "ap = " + ap);a.recycle();if (ap != INVALID_ID) {a = TintTypedArray.obtainStyledAttributes(context, ap, R.styleable.SkinTextAppearance);if (a.hasValue(R.styleable.SkinTextAppearance_android_textColor)) {mTextColorResId = a.getResourceId(R.styleable.SkinTextAppearance_android_textColor, INVALID_ID);SkinLog.d(TAG, "mTextColorResId = " + mTextColorResId);}if (a.hasValue(R.styleable.SkinTextAppearance_android_textColorHint)) {mTextColorHintResId = a.getResourceId(R.styleable.SkinTextAppearance_android_textColorHint, INVALID_ID);SkinLog.d(TAG, "mTextColorHintResId = " + mTextColorHintResId);}a.recycle();}// Now read the style's valuesa = TintTypedArray.obtainStyledAttributes(context, attrs, R.styleable.SkinTextAppearance,defStyleAttr, 0);if (a.hasValue(R.styleable.SkinTextAppearance_android_textColor)) {mTextColorResId = a.getResourceId(R.styleable.SkinTextAppearance_android_textColor, INVALID_ID);SkinLog.d(TAG, "mTextColorResId = " + mTextColorResId);}if (a.hasValue(R.styleable.SkinTextAppearance_android_textColorHint)) {mTextColorHintResId = a.getResourceId(R.styleable.SkinTextAppearance_android_textColorHint, INVALID_ID);SkinLog.d(TAG, "mTextColorHintResId = " + mTextColorHintResId);}a.recycle();applySkin();}public void onSetTextAppearance(Context context, int resId) {final TintTypedArray a = TintTypedArray.obtainStyledAttributes(context,resId, R.styleable.SkinTextAppearance);if (a.hasValue(R.styleable.SkinTextAppearance_android_textColor)) {mTextColorResId = a.getResourceId(R.styleable.SkinTextAppearance_android_textColor, INVALID_ID);SkinLog.d(TAG, "mTextColorResId = " + mTextColorResId);}if (a.hasValue(R.styleable.SkinTextAppearance_android_textColorHint)) {mTextColorHintResId = a.getResourceId(R.styleable.SkinTextAppearance_android_textColorHint, INVALID_ID);SkinLog.d(TAG, "mTextColorHintResId = " + mTextColorHintResId);}a.recycle();applySkin();}public void applySkin() {mTextColorResId = checkResourceId(mTextColorResId);if (mTextColorResId != INVALID_ID) {ColorStateList color = SkinCompatResources.getInstance().getColorStateList(mTextColorResId);mView.setTextColor(color);}mTextColorHintResId = checkResourceId(mTextColorHintResId);if (mTextColorHintResId != INVALID_ID) {ColorStateList color = SkinCompatResources.getInstance().getColorStateList(mTextColorHintResId);mView.setHintTextColor(color);}}
}

开发过程中遇到的一些问题

在5.0以上, 使用color为ImageView设置src, 可以通过getColorStateList获取资源, 而在5.0以下, 需要通过ColorDrawable setColor的方式实现

String typeName = mView.getResources().getResourceTypeName(mSrcResId);
if ("color".equals(typeName)) {if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {int color = SkinCompatResources.getInstance().getColor(mSrcResId);Drawable drawable = mView.getDrawable();if (drawable instanceof ColorDrawable) {((ColorDrawable) drawable.mutate()).setColor(color);} else {mView.setImageDrawable(new ColorDrawable(color));}} else {ColorStateList colorStateList = SkinCompatResources.getInstance().getColorStateList(mSrcResId);Drawable drawable = mView.getDrawable();DrawableCompat.setTintList(drawable, colorStateList);mView.setImageDrawable(drawable);}
} else if ("drawable".equals(typeName)) {Drawable drawable = SkinCompatResources.getInstance().getDrawable(mSrcResId);mView.setImageDrawable(drawable);
}

还有很多问题, 有兴趣的同学可以来一起交流解决.

总结

这样的做法与网上其他框架相比优势在哪里, 为什么重复造轮子
- 在增加框架开发成本的基础上降低了框架使用的成本, 我觉得更有意义, 一次开发, 所有Android 开发者都受用;
- 换肤框架对业务代码的侵入性比较小, 业务代码只需要继承自SkinCompatActivity, 不需要实现接口重写方法, 不需要其他额外的代码, 接入方便, 假如将来不想再使用本框架, 只需要把SkinCompatActivity改为原生Activity即可;
- 深入源码, 和源码实现方式类似, 兼容性更好.
为什么选择继承自AppCompatActivity, AppCompatTextView…而不是选择直接继承自Activity, TextView…
- 本身appcompat-v7包是一个support包, 兼容原生控件, 同时符合Material design, 我们只需要获取我们想要换肤的属性就可以在不破坏support包属性的前提下进行换肤;
- 参与开发的同学更多的话, 完全可以支持一套继承自Activity, TextView…的skin support包.
自定义View能否支持, 第三方控件是否支持换肤
- 答案是肯定的, 完全可以参照SkinCompatTextView的实现, 自己去实现自定义控件, 对于使用者来说, 扩展性很好.

源码地址: https://github.com/ximsfei/Android-skin-support