现象分析：
如果我们继承AppCompatActivity，我们在布局中添加一个TextView，但我们打印出来的这个TextView变成了AppCompatTextView，这种现象是如何实现的，我们来一起看一下源码（25）
1、我们先来看一下AppCompatActivity的setContentView的源码（实现跟Activity的setContentView的源码是差不多）
@Override
public void setContentView(@LayoutRes int layoutResID) {
getDelegate().setContentView(layoutResID);
}
这里的getDelegate()我们一路查看，最终发现他在最后做一些版本的判断
private static AppCompatDelegate create(Context context, Window window,
AppCompatCallback callback) {
final int sdk = Build.VERSION.SDK_INT;
if (BuildCompat.isAtLeastN()) {
return new AppCompatDelegateImplN(context, window, callback);
} else if (sdk >= 23) {
return new AppCompatDelegateImplV23(context, window, callback);
} else if (sdk >= 14) {
return new AppCompatDelegateImplV14(context, window, callback);
} else if (sdk >= 11) {
return new AppCompatDelegateImplV11(context, window, callback);
} else {
return new AppCompatDelegateImplV9(context, window, callback);
}
}
我们每个都打开看一下，发现在他们最终都继承自AppCompatDelegateImplV9这个类，所以我们前面的getDelegate()其实就是获取了一个AppCompatDelegateImplV9的实例，接下来我们来看一下AppCompatDelegateImplV9中的setContentView，这里就跟Activity的setContentView非常相似了， 详见： http://www.jianshu.com/p/1221871c7cd5
@Override
public void setContentView(int resId) {
ensureSubDecor();
ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
contentParent.removeAllViews();
LayoutInflater.from(mContext).inflate(resId, contentParent);
mOriginalWindowCallback.onContentChanged();
}
inflate创建view的时候会有一句比较关键的代码： （如果inflate创建view过程不熟的同鞋，详见inflate创建view ： http://www.jianshu.com/p/97e5f7b61b3b）
final View temp = createViewFromTag(root, name, inflaterContext, attrs);
接下来我们来看一下这个createViewFromTag方法
View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
boolean ignoreThemeAttr) {
// ...
try {
View view;
if (mFactory2 != null) {
view = mFactory2.onCreateView(parent, name, context, attrs);
} else if (mFactory != null) {
view = mFactory.onCreateView(name, context, attrs);
} else {
view = null;
}
if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, context, attrs);
}
if (view == null) {
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
if (-1 == name.indexOf('.')) {
view = onCreateView(parent, name, attrs);
} else {
view = createView(name, null, attrs);
}
} finally {
mConstructorArgs[0] = lastContext;
}
}
return view;
} catch (InflateException e) {
// ...
}
}
重点来了，请看5-29行，如果有设置Factory，则创建由Factory的onCreateView来创建view，如果没有Factory则由系统去创建view，
这时我们就可以大胆的猜想AppCompatActivity拦截view的创建过程应该就是这个Factory来起作用了。
2、下面我们再回到AppCompatActivity中，看他到底是怎么设置这个Factory的
我们来看一下AppCompatActivity的onCreate方法
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
final AppCompatDelegate delegate = getDelegate();
delegate.installViewFactory();
delegate.onCreate(savedInstanceState);
// ...
super.onCreate(savedInstanceState);
}
还记得我们在一开始看setContentView()的时候getDelegate() 得到的结论嘛？ getDelegate() 其实就是获取了一个AppCompatDelegateImplV9的实例
delegate.installViewFactory();这个方法看着挺像的样子，我们来到 AppCompatDelegateImplV9 类中具体看一下
@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");
}
}
}
关键的方法来了，这里就是我们要找的设置Factory的具体方法，这个时候就会由Factory设置好的onCreateView方法来创建view
@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);
}
@Override
public View createView(View parent, final String name, @NonNull Context context,
@NonNull AttributeSet attrs) {
if (mAppCompatViewInflater == null) {
mAppCompatViewInflater = new AppCompatViewInflater();
}
// ...
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 */
);
}
public final View createView(View parent, final String name, @NonNull Context context,
@NonNull AttributeSet attrs, boolean inheritContext,
boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {
final Context originalContext = context;
// ...
View view = null;
// We 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;
}
if (view == null && originalContext != context) {
view = createViewFromTag(context, name, attrs);
}
if (view != null) {
checkOnClickListener(view, attrs);
}
return view;
}
到这里我们就能很明显的看到，他在这里把我们的TextView变成了AppCompatTextView。
如果我们也有拦截View的需求，我们也可以参考源码这样来写。
