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
通过第一部分我们知道可以通过复写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);
}
}
