Android-skin-support: 实现原理

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 {    @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {        final AppCompatDelegate delegate = getDelegate();        delegate.installViewFactory();        delegate.onCreate(savedInstanceState);        ...    }    @Override    public MenuInflater getMenuInflater() {        return getDelegate().getMenuInflater();    }    @Override    public void setContentView(@LayoutRes int layoutResID) {        getDelegate().setContentView(layoutResID);    }    @Override    public 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 AppCompatDelegateImplBase        implements MenuBuilder.Callback, LayoutInflaterFactory {    @Override    public 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

@Overridepublic final View onCreateView(View parent, String name,        Context context, AttributeSet attrs) {    // First let the Activity's Factory try and inflate the view    final View view = callActivityOnCreateView(parent, name, context, attrs);    if (view != null) {        return view;    }    // If the Factory didn't handle it, let our createView() method try    return createView(parent, name, context, attrs);}@Overridepublic 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-v21    final 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();    }    @Override    public 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);    }    @Override    public void setBackgroundResource(@DrawableRes int resId) {        super.setBackgroundResource(resId);        if (mBackgroundTintHelper != null) {            mBackgroundTintHelper.onSetBackgroundResource(resId);        }    }    @Override    public void setTextAppearance(Context context, int resId) {        super.setTextAppearance(context, resId);        if (mTextHelper != null) {            mTextHelper.onSetTextAppearance(context, resId);        }    }    @Override    public 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 id        TintTypedArray 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 values        a = 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

1. 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.

2. 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.

3. 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