[TOC]
原始地址：日夜间及换肤（二）-原理分析
官方原理
在官方的推荐方法中，我们发现了每次设置完Mode或者Theme都需要recreate()才会生效，这是为什么呢？
/**
* Cause this Activity to be recreated with a new instance. This results
* in essentially the same flow as when the Activity is created due to
* a configuration change -- the current instance will go through its
* lifecycle to {@link #onDestroy} and a new instance then created after it.
*/
使用新实例重新创建此活动。 这导致与由于配置更改而创建 Activity 时的流程基本相同————当前实例将通过其生命周期到达onDestroy ，然后在它之后创建一个新实例
即当前Activity进入onDestroy，重新创建一个Activity，所以会执行新Activity的生命周期
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
final AppCompatDelegate delegate = getDelegate();
delegate.installViewFactory();
delegate.onCreate(savedInstanceState);
super.onCreate(savedInstanceState);
}
进入delegate.onCreate()方法中
@Override
public void onCreate(Bundle savedInstanceState) {
// attachBaseContext will only be called from an Activity, so make sure we switch this for
// Dialogs, etc
mBaseContextAttached = true;
// Our implicit call to applyDayNight() should not recreate until after the Activity is
// created
applyDayNight(false);
...
}
点击进入applyDayNight方法中
private boolean applyDayNight(final boolean allowRecreation) {
if (mIsDestroyed) {
if (DEBUG) {
Log.d(TAG, "applyDayNight. Skipping because host is destroyed");
}
// If we're destroyed, ignore the call
return false;
}
@NightMode final int nightMode = calculateNightMode();
...
}
进入calculateNightMode()中
@NightMode
private int calculateNightMode() {
return mLocalNightMode != MODE_NIGHT_UNSPECIFIED ? mLocalNightMode : getDefaultNightMode();
}
public static int getDefaultNightMode() {
return sDefaultNightMode;
}
public static void setDefaultNightMode(@NightMode int mode) {
...
switch (mode) {
case MODE_NIGHT_NO:
case MODE_NIGHT_YES:
case MODE_NIGHT_FOLLOW_SYSTEM:
case MODE_NIGHT_AUTO_TIME:
case MODE_NIGHT_AUTO_BATTERY:
if (sDefaultNightMode != mode) {
sDefaultNightMode = mode;
applyDayNightToActiveDelegates();
}
break;
default:
Log.d(TAG, "setDefaultNightMode() called with an unknown mode");
break;
}
}
获取mode类型后进行加载日夜间效果，所以在该方式下要达到动态切换，势必要重新执行onCreate方法
androidx中sdk中已经将recreate方法放入setDefaultNightMode()方法中，所以不需要手动调用
无论通过AppCompatDelegate.setDefaultNightMode还是delegate.setLocalNightMode，都会执行到updateForNightMode方法
private boolean updateForNightMode(@ApplyableNightMode final int mode,
final boolean allowRecreation) {
...
ActivityCompat.recreate((Activity) mHost);
handled = true;
...
return handled;
}
执行recreate重新构建Activity
第三方库实现原理
原理分析（SdkVersion = 29）
怎么做到的呢？
我们回顾一下setContentView()的加载过程：
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
//androidx.appcompat.app.AppcompatActivity
@Override
public void setContentView(@LayoutRes int layoutResID) {
getDelegate().setContentView(layoutResID);
}
进入代理中查看实现：
//androidx.appcompat.app.AppcompatDelegateImpl
@Override
public void setContentView(int resId) {
//初始化DecroView
ensureSubDecor();
//获取Content根布局
ViewGroup contentParent = mSubDecor.findViewById(android.R.id.content);
//移除所有布局
contentParent.removeAllViews();
//加载布局
LayoutInflater.from(mContext).inflate(resId, contentParent);
//布局状态接口通知
mAppCompatWindowCallback.getWrapped().onContentChanged();
}
进入inflate方法中：
//android.view.LayoutInflater
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
return inflate(resource, root, root != null);
}
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
final Resources res = getContext().getResources();
...
// 根据XML预编译生成compiled_view.dex, 然后通过反射来生成对应的View，从而减少XmlPullParser解析Xml的时间
// 需要注意的是在目前的release版本中不支持使用
View view = tryInflatePrecompiled(resource, res, root, attachToRoot);
if (view != null) {
return view;
}
//使用xml进行解析返回一个XmlResourceParser，内部最终会进入native方法进行解析
XmlResourceParser parser = res.getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}
进入inflate中：
//android.view.LayoutInflater
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
...
try {
//找到START_TAG，否则报异常，说没有入口
advanceToRootNode(parser);
final String name = parser.getName();
...
//如果是merge标签，查看merge是不是根节点，不然的话抛出异常
if (TAG_MERGE.equals(name)) {
if (root == null || !attachToRoot) {
throw new InflateException("<merge /> can be used only with a valid "
+ "ViewGroup root and attachToRoot=true");
}
rInflate(parser, root, inflaterContext, attrs, false);
} else {
// Temp is the root view that was found in the xml
//获取根节点View
final View temp = createViewFromTag(root, name, inflaterContext, attrs);
...
//渲染根节点的孩子们
rInflateChildren(parser, temp, attrs, true);
...
return result;
}
}
进入rInflateChildren()中：
final void rInflateChildren(XmlPullParser parser, View parent, AttributeSet attrs,
boolean finishInflate) throws XmlPullParserException, IOException {
rInflate(parser, parent, parent.getContext(), attrs, finishInflate);
}
void rInflate(XmlPullParser parser, View parent, Context context,
AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {
final int depth = parser.getDepth();
int type;
boolean pendingRequestFocus = false;
//循环便利布局，直到布局完成
while (((type = parser.next()) != XmlPullParser.END_TAG ||
parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
...
//获取当前布局的View
final View view = createViewFromTag(parent, name, context, attrs);
final ViewGroup viewGroup = (ViewGroup) parent;
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
//渲染当前布局View的孩子们
rInflateChildren(parser, view, attrs, true);
//组合为ViewGroup
viewGroup.addView(view, params);
}
}
if (pendingRequestFocus) {
parent.restoreDefaultFocus();
}
if (finishInflate) {
parent.onFinishInflate();
}
}
进入createViewFromTag():
//android.view.LayoutInflater
View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
boolean ignoreThemeAttr) {
if (name.equals("view")) {
name = attrs.getAttributeValue(null, "class");
}
// Apply a theme wrapper, if allowed and one is specified.
if (!ignoreThemeAttr) {
final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
final int themeResId = ta.getResourceId(0, 0);
if (themeResId != 0) {
context = new ContextThemeWrapper(context, themeResId);
}
ta.recycle();
}
try {
View view = tryCreateView(parent, name, context, attrs);
if (view == null) {
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
if (-1 == name.indexOf('.')) {
view = onCreateView(context, parent, name, attrs);
} else {
view = createView(context, name, null, attrs);
}
} finally {
mConstructorArgs[0] = lastContext;
}
}
return view;
} catch (InflateException e) {
...
}
}
进行tryCreateView方法，如果view为null，则执行onCreateView或者createView方法，
无论是onCreateView还是createView最终都会进入如下函数：
@Nullable
public final View createView(@NonNull Context viewContext, @NonNull String name,
@Nullable String prefix, @Nullable AttributeSet attrs)
throws ClassNotFoundException, InflateException {
Objects.requireNonNull(viewContext);
Objects.requireNonNull(name);
Constructor<? extends View> constructor = sConstructorMap.get(name);
if (constructor != null && !verifyClassLoader(constructor)) {
constructor = null;
sConstructorMap.remove(name);
}
Class<? extends View> clazz = null;
try {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, name);
if (constructor == null) {
// Class not found in the cache, see if it's real, and try to add it
clazz = Class.forName(prefix != null ? (prefix + name) : name, false,
mContext.getClassLoader()).asSubclass(View.class);
if (mFilter != null && clazz != null) {
boolean allowed = mFilter.onLoadClass(clazz);
if (!allowed) {
failNotAllowed(name, prefix, viewContext, attrs);
}
}
constructor = clazz.getConstructor(mConstructorSignature);
constructor.setAccessible(true);
sConstructorMap.put(name, constructor);
} else {
// If we have a filter, apply it to cached constructor
if (mFilter != null) {
// Have we seen this name before?
Boolean allowedState = mFilterMap.get(name);
if (allowedState == null) {
// New class -- remember whether it is allowed
clazz = Class.forName(prefix != null ? (prefix + name) : name, false,
mContext.getClassLoader()).asSubclass(View.class);
boolean allowed = clazz != null && mFilter.onLoadClass(clazz);
mFilterMap.put(name, allowed);
if (!allowed) {
failNotAllowed(name, prefix, viewContext, attrs);
}
} else if (allowedState.equals(Boolean.FALSE)) {
failNotAllowed(name, prefix, viewContext, attrs);
}
}
}
Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = viewContext;
Object[] args = mConstructorArgs;
args[1] = attrs;
try {
final View view = constructor.newInstance(args);
if (view instanceof ViewStub) {
// Use the same context when inflating ViewStub later.
final ViewStub viewStub = (ViewStub) view;
viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
}
return view;
} finally {
mConstructorArgs[0] = lastContext;
}
} catch (NoSuchMethodException e) {
...
}
}
简单看一下可以确认是通过反射实现的
然后我们进入tryCreateView()方法：
//android.view.LayoutInflater
public final View tryCreateView(@Nullable View parent, @NonNull String name,
@NonNull Context context,
@NonNull AttributeSet attrs) {
if (name.equals(TAG_1995)) {
// Let's party like it's 1995!
return new BlinkLayout(context, attrs);
}
View view;
if (mFactory2 != null) {
//系统一般会创建Factory2的对象
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);
}
return view;
}
那这个mFactory2/mFactory.onCreateView()要走哪里呢？Factory实例在哪里呢？
接下来
我们需要分析setContenView()之前都做了什么
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
点击super.onCreate(saveInstanceState)方法：
//androidx.appcompat.app.AppCompatActivity
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
final AppCompatDelegate delegate = getDelegate();
delegate.installViewFactory();
delegate.onCreate(savedInstanceState);
super.onCreate(savedInstanceState);
}
进入installViewFactory()方法：
//androidx.appcompat.app.AppCompatDelegateImpl
@Override
public void installViewFactory() {
LayoutInflater layoutInflater = LayoutInflater.from(mContext);
if (layoutInflater.getFactory() == null) {
LayoutInflaterCompat.setFactory2(layoutInflater, this);
} else {
if (!(layoutInflater.getFactory2() instanceof AppCompatDelegateImpl)) {
Log.i(TAG, "The Activity's LayoutInflater already has a Factory installed"
+ " so we can not install AppCompat's");
}
}
}
首先通过获取layoutInflater.getFactory()进行获取，如果没有就会setFactory2进行设置。
在其中进行setFactory初始化，注意第二个参数，传入的是this，那么，我们看一下这个类：
class AppCompatDelegateImpl extends AppCompatDelegate
implements MenuBuilder.Callback, LayoutInflater.Factory2
很好，他是一个实现Factory2接口的类，那么我们直接找onCreateView的实现：
@Override
public View createView(View parent, final String name, @NonNull Context context,
@NonNull AttributeSet attrs) {
...
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 */
);
}
其实调用的是AppcompatViewInflater.createView()方法：
final View createView(View parent, final String name, @NonNull Context context,
@NonNull AttributeSet attrs, boolean inheritContext,
boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {
...
switch (name) {
case "TextView":
view = createTextView(context, attrs);
verifyNotNull(view, name);
break;
...
default:
// The fallback that allows extending class to take over view inflation
// for other tags. Note that we don't check that the result is not-null.
// That allows the custom inflater path to fall back on the default one
// later in this method.
view = createView(context, name, attrs);
}
...
return view;
}
@NonNull
protected AppCompatTextView createTextView(Context context, AttributeSet attrs) {
return new AppCompatTextView(context, attrs);
}
通过new的方式新建view，如果switch没有得到处理，则返回view为null，通过反射处理即可
我们要怎么做？
Factory和Factory2的区别是什么？
可惜我们不能从文档说明上获得什么，我们就直接看代码吧
public interface Factory {
@Nullable
View onCreateView(@NonNull String name, @NonNull Context context,
@NonNull AttributeSet attrs);
}
public interface Factory2 extends Factory {
@Nullable
View onCreateView(@Nullable View parent, @NonNull String name,
@NonNull Context context, @NonNull AttributeSet attrs);
}
字段中多了一个View的父类，可以认为Factory2是对Factory的重载
在分析过程中，我们发现
//androidx.appcompat.app.AppCompatDelegateImpl
@Override
public void installViewFactory() {
LayoutInflater layoutInflater = LayoutInflater.from(mContext);
if (layoutInflater.getFactory() == null) {
LayoutInflaterCompat.setFactory2(layoutInflater, this);
} else {
if (!(layoutInflater.getFactory2() instanceof AppCompatDelegateImpl)) {
Log.i(TAG, "The Activity's LayoutInflater already has a Factory installed"
+ " so we can not install AppCompat's");
}
}
}
系统的处理是默认会取Factory，如果没有，才会新建，走AppCompatDelegateImpl，如果我们在这个super.onCreate()方法之前设置Factory就可以让系统走我们的Factory实现
具体实现
最终我们在Activity的onCreate方法之前执行我们的设置
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
LayoutInflaterCompat.setFactory(getLayoutInflater(), getSkinDelegate());
super.onCreate(savedInstanceState);
}
同时在createView方法中生成自己的view，在view中设置刷新接口，通过观察者模式在模式变化的时候穿心所有的view，变更背景色，字体色等，不需要重新构建Activity，避免闪屏
