Android-skin-support的原理

前言

上一篇阐述了皮肤包的创建和配置使用Android-skin-support生成换肤包，那么这一篇文章我们就来阐述一下Android-skin-support的原理。

正文

让我们先看看v7包中的AppCompatActivity是如何实现加载布局资源的。
AppCompatActivity的是生命周期是委托给AppCompateDelegate的子类AppCompatDelegateImplV9来实现。在AppCompatDelegateImplV9中我们看到了LayoutInflater 这个类。

@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");            }        }

还是在AppCompatDelegateImplV9的类中，有个onCreateView()方法，这个方法是LayoutInflaterFactory接口的方法（AppCompatDelegateImplV9实现了LayoutInflaterFactory的接口）这方法的View又是通过createview()方法交给AppCompatViewInflater处理的。

 /**     * From {@link android.support.v4.view.LayoutInflaterFactory}     */    @Override    public 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);    }

我们注意createView方法的mAppCompatViewInflater.createView()这一行代码,此代码跳到就是跳到AppCompatViewInflater.createView中的createView()方法。

 @Override    public View createView(View parent, final String name, @NonNull Context context,            @NonNull AttributeSet attrs) {        if (mAppCompatViewInflater == null) {            mAppCompatViewInflater = new AppCompatViewInflater();        }        boolean inheritContext = false;        if (IS_PRE_LOLLIPOP) {            inheritContext = (attrs instanceof XmlPullParser)                    // If we have a XmlPullParser, we can detect where we are in the layout                    ? ((XmlPullParser) attrs).getDepth() > 1                    // Otherwise we have to use the old heuristic                    : shouldInheritContext((ViewParent) parent);        }        return mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext,                IS_PRE_LOLLIPOP, /* 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 */        );    }

查看AppCompatViewInflater.createView中的createView()的方法

 public final View createView(View parent, final String name, @NonNull Context context,            @NonNull AttributeSet attrs, boolean inheritContext,            boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) { need to 'inject' our tint aware Views in place of the standard framework versions        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;            case "RadioButton":                view = new AppCompatRadioButton(context, attrs);                break;            case "CheckedTextView":                view = new AppCompatCheckedTextView(context, attrs);                break;            case "AutoCompleteTextView":                view = new AppCompatAutoCompleteTextView(context, attrs);                break;            case "MultiAutoCompleteTextView":                view = new AppCompatMultiAutoCompleteTextView(context, attrs);                break;            case "RatingBar":                view = new AppCompatRatingBar(context, attrs);                break;            case "SeekBar":                view = new AppCompatSeekBar(context, attrs);                break;        }        return view;    }

我们看到有很多控件的分类，在这些控件中（比如AppCompatImageView）借助AppCompatBackgroundHelper完成了相关子控件背景的设置。

AppCompatImageView中的构造函数

   public AppCompatImageView(Context context, AttributeSet attrs, int defStyleAttr) {        super(TintContextWrapper.wrap(context), attrs, defStyleAttr);        mBackgroundTintHelper = new AppCompatBackgroundHelper(this);        mBackgroundTintHelper.loadFromAttributes(attrs, defStyleAttr);        mImageHelper = new AppCompatImageHelper(this);        mImageHelper.loadFromAttributes(attrs, defStyleAttr);    }

在AppCompatBackgroundHelper中判断attr中是否为此控件的android_background设置了背景，如果设置了就取出

 void loadFromAttributes(AttributeSet attrs, int defStyleAttr) {        TintTypedArray a = TintTypedArray.obtainStyledAttributes(mView.getContext(), attrs,                R.styleable.ViewBackgroundHelper, defStyleAttr, 0);        try {            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);                }            }            if (a.hasValue(R.styleable.ViewBackgroundHelper_backgroundTint)) {                ViewCompat.setBackgroundTintList(mView,                        a.getColorStateList(R.styleable.ViewBackgroundHelper_backgroundTint));            }            if (a.hasValue(R.styleable.ViewBackgroundHelper_backgroundTintMode)) {                ViewCompat.setBackgroundTintMode(mView,                        DrawableUtils.parseTintMode(                                a.getInt(R.styleable.ViewBackgroundHelper_backgroundTintMode, -1),                                null));            }        } finally {            a.recycle();        }    }

前言

上一篇阐述了皮肤包的创建和配置使用Android-skin-support生成换肤包，那么这一篇文章我们就来阐述一下Android-skin-support的原理。

正文

第一部分

让我们先看看v7包中的AppCompatActivity是如何实现加载布局的。
AppCompatActivity的是生命周期是委托给AppCompateDelegate的子类AppCompatDelegateImplV9来实现。在AppCompatDelegateImplV9中我们看到了LayoutInflater 这个类。

@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");            }        }

还是在AppCompatDelegateImplV9的类中，有个onCreateView()方法，这个方法是LayoutInflaterFactory接口的方法（AppCompatDelegateImplV9实现了LayoutInflaterFactory的接口）这方法的View又是通过createview()方法交给AppCompatViewInflater处理的。

 /**     * From {@link android.support.v4.view.LayoutInflaterFactory}     */    @Override    public 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);    }

我们注意createView方法的mAppCompatViewInflater.createView()这一行代码,此代码跳到就是跳到AppCompatViewInflater.createView中的createView()方法。

 @Override    public View createView(View parent, final String name, @NonNull Context context,            @NonNull AttributeSet attrs) {        if (mAppCompatViewInflater == null) {            mAppCompatViewInflater = new AppCompatViewInflater();        }        boolean inheritContext = false;        if (IS_PRE_LOLLIPOP) {            inheritContext = (attrs instanceof XmlPullParser)                    // If we have a XmlPullParser, we can detect where we are in the layout                    ? ((XmlPullParser) attrs).getDepth() > 1                    // Otherwise we have to use the old heuristic                    : shouldInheritContext((ViewParent) parent);        }        return mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext,                IS_PRE_LOLLIPOP, /* 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 */        );    }

查看AppCompatViewInflater中的createView()的方法

 public final View createView(View parent, final String name, @NonNull Context context,            @NonNull AttributeSet attrs, boolean inheritContext,            boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) { need to 'inject' our tint aware Views in place of the standard framework versions        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;            case "RadioButton":                view = new AppCompatRadioButton(context, attrs);                break;            case "CheckedTextView":                view = new AppCompatCheckedTextView(context, attrs);                break;            case "AutoCompleteTextView":                view = new AppCompatAutoCompleteTextView(context, attrs);                break;            case "MultiAutoCompleteTextView":                view = new AppCompatMultiAutoCompleteTextView(context, attrs);                break;            case "RatingBar":                view = new AppCompatRatingBar(context, attrs);                break;            case "SeekBar":                view = new AppCompatSeekBar(context, attrs);                break;        }        return view;    }

我们看到有很多控件的分类，在这些控件中（比如AppCompatImageView）借助AppCompatBackgroundHelper和AppCompatImageHelper完成了相关子控件背景的设置。

AppCompatImageView中的构造函数

   public AppCompatImageView(Context context, AttributeSet attrs, int defStyleAttr) {        super(TintContextWrapper.wrap(context), attrs, defStyleAttr);        mBackgroundTintHelper = new AppCompatBackgroundHelper(this);        mBackgroundTintHelper.loadFromAttributes(attrs, defStyleAttr);        mImageHelper = new AppCompatImageHelper(this);        mImageHelper.loadFromAttributes(attrs, defStyleAttr);    }

在ImageHelper中解析attr中为此控件的AppCompatImageView_srcCompat设置的图片资源和android_background设置的背景资源后保存。如果设置了就取出设置drawable，通过BackgroundTintHelper设置背景，并drawable.invalidateSelf()。

   public void loadFromAttributes(AttributeSet attrs, int defStyleAttr) {        TintTypedArray a = null;        try {            Drawable drawable = mView.getDrawable();            if (drawable == null) {                a = TintTypedArray.obtainStyledAttributes(mView.getContext(), attrs,                        R.styleable.AppCompatImageView, defStyleAttr, 0);                // If the view doesn't already have a drawable (from android:src), try loading                // it from srcCompat                final int id = a.getResourceId(R.styleable.AppCompatImageView_srcCompat, -1);                if (id != -1) {                    drawable = AppCompatResources.getDrawable(mView.getContext(), id);                    if (drawable != null) {                        mView.setImageDrawable(drawable);                    }                }            }            if (drawable != null) {                DrawableUtils.fixDrawable(drawable);            }        } finally {            if (a != null) {                a.recycle();            }        }    }

 void applySupportBackgroundTint() {        final Drawable background = mView.getBackground();            if (mBackgroundTint != null) {                AppCompatDrawableManager.tintDrawable(background, mBackgroundTint,                        mView.getDrawableState());            } else if (mInternalBackgroundTint != null) {                AppCompatDrawableManager.tintDrawable(background, mInternalBackgroundTint,                        mView.getDrawableState());            }        }

第二部分

基本原理
通过第一部分的原理我们可知，可以通过复写SkinCompatViewInflater代替AppCompatViewInflater，并将LayoutInflateFactor中的View的创建过程交给SkinCompatViewInflater类来实现。在此类中的createViewFromFV()方法中实现自定义的控件（比如SkinCompatView），再从写setBackgroundResource方法实现换肤。

1.所有的控件都要实现SkinCompatSupportable这个接口，这个接口中只有一个方法applySkin()。每次skinCompatManager.loadSkin()切换皮肤的时候就会调用applySkin()方法。

public interface SkinCompatSupportable {    void applySkin();}

下面的就是实现SkinCompatSupportable的SkinCompatImageView

public class SkinCompatImageView extends AppCompatImageView implements SkinCompatSupportable {    private SkinCompatBackgroundHelper mBackgroundTintHelper;    private SkinCompatImageHelper mImageHelper;    public SkinCompatImageView(Context context) {        this(context, (AttributeSet)null);    }    public SkinCompatImageView(Context context, AttributeSet attrs) {        this(context, attrs, 0);    }    public SkinCompatImageView(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        this.mBackgroundTintHelper = new SkinCompatBackgroundHelper(this);        this.mBackgroundTintHelper.loadFromAttributes(attrs, defStyleAttr);        this.mImageHelper = new SkinCompatImageHelper(this);        this.mImageHelper.loadFromAttributes(attrs, defStyleAttr);    }    public void setBackgroundResource(@DrawableRes int resId) {        super.setBackgroundResource(resId);        if(this.mBackgroundTintHelper != null) {            this.mBackgroundTintHelper.onSetBackgroundResource(resId);        }    }    public void setImageResource(@DrawableRes int resId) {        if(this.mImageHelper != null) {            this.mImageHelper.setImageResource(resId);        }    }    public void applySkin() {        if(this.mBackgroundTintHelper != null) {            this.mBackgroundTintHelper.applySkin();        }        if(this.mImageHelper != null) {            this.mImageHelper.applySkin();        }    }}

在构造方法中通过在构造方法中通过SkinCompatBackgroundHelper和SkinCompatImageHelper通过loadFromAttributes分别解析出background, drawbale并保存，然后调用applySkin()方法完成图片的更换或者背景的设置。

  public void loadFromAttributes(AttributeSet attrs, int defStyleAttr) {        TypedArray a = null;        try {            a = this.mView.getContext().obtainStyledAttributes(attrs, styleable.SkinCompatImageView, defStyleAttr, 0);            this.mSrcResId = a.getResourceId(styleable.SkinCompatImageView_android_src, 0);            int srcCompatResId = a.getResourceId(styleable.SkinCompatImageView_srcCompat, 0);            srcCompatResId = checkResourceId(srcCompatResId);            if(srcCompatResId != 0) {                this.mSrcResId = srcCompatResId;            }        } finally {            if(a != null) {                a.recycle();            }        }        this.applySkin();    }

上面的就是在SkinCompatImageView初始化的时候通过过SkinCompatBackgroundHelper和SkinCompatImageHelper 调用applySkin()完成换肤的。那么如果初始化完成后通过点击按钮用skinCompatManager.loadSkin()实现换肤该怎么办呢，其实我们前面说过SkinCompatImageView都继承了SkinCompatSupportable，当加载切换不同的皮肤包后SkinCompatSupportable接口中的applySkin()的方法就被会执行,方法会调用SkinCompatBackgroundHelper和SkinCompatImageHelper 的applySkin()方法完成换肤。

  public void applySkin() {        if(this.mBackgroundTintHelper != null) {            this.mBackgroundTintHelper.applySkin();        }        if(this.mImageHelper != null) {            this.mImageHelper.applySkin();        }    }

调用applySkin完成图片的更换和背景的设置

 public void applySkin() {        this.mSrcResId = checkResourceId(this.mSrcResId);        SkinLog.d(TAG, "mSrcResId = " + this.mSrcResId);        if(this.mSrcResId != 0) {            String typeName = this.mView.getResources().getResourceTypeName(this.mSrcResId);            if("color".equals(typeName)) {                Drawable drawable1;                if(VERSION.SDK_INT < 21) {                    int drawable = SkinCompatResources.getInstance().getColor(this.mSrcResId);                    drawable1 = this.mView.getDrawable();                    if(drawable1 != null && drawable1 instanceof ColorDrawable) {                        ((ColorDrawable)drawable1.mutate()).setColor(drawable);                    } else {                        this.mView.setImageDrawable(new ColorDrawable(drawable));                    }                } else {                    ColorStateList drawable2 = SkinCompatResources.getInstance().getColorStateList(this.mSrcResId);                    drawable1 = this.mView.getDrawable();                    if(drawable1 != null) {                        DrawableCompat.setTintList(drawable1, drawable2);                        this.mView.setImageDrawable(drawable1);                    } else {                        ColorDrawable colorDrawable = new ColorDrawable();                        colorDrawable.setTintList(drawable2);                        this.mView.setImageDrawable(colorDrawable);                    }                }            } else {                Drawable drawable3;                if("drawable".equals(typeName)) {                    drawable3 = SkinCompatResources.getInstance().getDrawable(this.mSrcResId);                    this.mView.setImageDrawable(drawable3);                } else if("mipmap".equals(typeName)) {                    drawable3 = SkinCompatResources.getInstance().getMipmap(this.mSrcResId);                    this.mView.setImageDrawable(drawable3);                }            }

其实Android-skin-support还是有部分缺陷的，有些皮肤或者高度之类的变换无法实现，那么下一篇我们就来看看Android-skin-support的缺陷。

Android-skin-support的缺陷