【重拾View(三)】——LayoutInflater中Fact
2018-11-04 本文已影响5人
被代码淹没的小伙子
1.【重拾View(一)】——setContentView()源码解析
2.【重拾View(二)】——LayoutInflater源码解析
3.【重拾View(三)】——LayoutInflater中Factory源码解析
前言
上一篇博客分析了LayoutInflater的inflate方法，可以说对inflate已经有了一个比较全面的认识，这里专门抽出一片博客专门分析一下LayoutInflater中的Factory相关的源码解析，因为这算是Google处理解析的一个小插曲，利用这个Factory我们可以完成很多自定义解析方式，有很多框架实质都是基于这个原理。
源码解析
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;
}
...
这里放上了上一篇博客分析的解析创建View的关键方法createViewFromTag，可以看到在创建的一开始，首先有三处判断条件，分辨判断了mFactory2，mFactory，mPrivateFactory的onCreateView方法来创建View。如果这三个创建出的View！=null ,则直接返回了这个View.
这里其实三个都是LayoutInflater的成员变量，都有对应的set和get方法。所以这里我们关注一下这三个的定义。
private Factory mFactory;
private Factory2 mFactory2;
private Factory2 mPrivateFactory;
public interface Factory {
public View onCreateView(String name, Context context, AttributeSet attrs);
}
public interface Factory2 extends Factory {
public View onCreateView(View parent, String name, Context context, AttributeSet attrs);
}
其实可以看到就是简单的两个接口，并且Factory2继承了Factory。其实两者也有一定的区别：
- LayoutInflater.Factory2 是API 11 被加进来的；
- 可以对创建 View 的 Parent 进行控制,方法参数中多了
parent；
- 可以对创建 View 的 Parent 进行控制,方法参数中多了
为什么说是是API 11 被加进来的呢？既然说到了API11，那么我们来看一下API11对应的AppCompatActivity的源码
AppCompatActivity源码分析
public class AppCompatActivity extends FragmentActivity implements AppCompatCallback, SupportParentable, DelegateProvider {
protected void onCreate(@Nullable Bundle savedInstanceState) {
AppCompatDelegate delegate = this.getDelegate();、
//设置Factory工厂
delegate.installViewFactory();
delegate.onCreate(savedInstanceState);
if(delegate.applyDayNight() && this.mThemeId != 0) {
if(VERSION.SDK_INT >= 23) {
this.onApplyThemeResource(this.getTheme(), this.mThemeId, false);
} else {
this.setTheme(this.mThemeId);
}
}
super.onCreate(savedInstanceState);
}
这里可以看到，在AppCompatActivity的onCreate方法中，调用了delegate.installViewFactory();方法，这里就利用LayoutInflater的Factory进行了设置。
public static AppCompatDelegate create(Activity activity, AppCompatCallback callback) {
return create(activity, activity.getWindow(), callback);
}
private static AppCompatDelegate create(Context context, Window window, AppCompatCallback callback) {
return (AppCompatDelegate)(VERSION.SDK_INT >= 24?new AppCompatDelegateImplN(context, window, callback):(VERSION.SDK_INT >= 23?new AppCompatDelegateImplV23(context, window, callback):(VERSION.SDK_INT >= 14?new AppCompatDelegateImplV14(context, window, callback):(VERSION.SDK_INT >= 11?new AppCompatDelegateImplV11(context, window, callback):new AppCompatDelegateImplV9(context, window, callback)))));
}
关于AppCompatDelegate可以看到就是不同的版本判断得到不同的类，经常看源码的应该都清楚，这里一般不同版本都是继承关系，所以这里我们就来看一下AppCompatDelegateImplV9，不出意外installViewFactory方法在这里面就有定义。
class AppCompatDelegateImplV9 extends AppCompatDelegateImplBase implements Callback, Factory2 {
public void installViewFactory() {
LayoutInflater layoutInflater = LayoutInflater.from(this.mContext);
if(layoutInflater.getFactory() == null) {
LayoutInflaterCompat.setFactory2(layoutInflater, this);
} else if(!(layoutInflater.getFactory2() instanceof AppCompatDelegateImplV9)) {
Log.i("AppCompatDelegate", "The Activity's LayoutInflater already has a Factory installed so we can not install AppCompat's");
}
}
public final View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
View view = this.callActivityOnCreateView(parent, name, context, attrs);
return view != null?view:this.createView(parent, name, context, attrs);
}
public View createView(View parent, String name, @NonNull Context context, @NonNull AttributeSet attrs) {
if(this.mAppCompatViewInflater == null) {
this.mAppCompatViewInflater = new AppCompatViewInflater();
}
boolean inheritContext = false;
if(IS_PRE_LOLLIPOP) {
inheritContext = attrs instanceof XmlPullParser?((XmlPullParser)attrs).getDepth() > 1:this.shouldInheritContext((ViewParent)parent);
}
return this.mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext, IS_PRE_LOLLIPOP, true, VectorEnabledTintResources.shouldBeUsed());
}
}
可以看到果不其然，这里利用LayoutInflater设置了一个Factory、可以看到最终会调用createView方法，并且创建了一个AppCompatViewInflater，并调用了其createView方法。
public final View createView(View parent, String name, @NonNull Context context, @NonNull AttributeSet attrs, boolean inheritContext, boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {
if(inheritContext && parent != null) {
context = parent.getContext();
}
if(readAndroidTheme || readAppTheme) {
context = themifyContext(context, attrs, readAndroidTheme, readAppTheme);
}
if(wrapContext) {
context = TintContextWrapper.wrap(context);
}
View view = null;
byte var12 = -1;
switch(name.hashCode()) {
case -1946472170:
if(name.equals("RatingBar")) {
var12 = 11;
}
break;
case -1455429095:
if(name.equals("CheckedTextView")) {
var12 = 8;
}
break;
case -1346021293:
if(name.equals("MultiAutoCompleteTextView")) {
var12 = 10;
}
break;
case -938935918:
if(name.equals("TextView")) {
var12 = 0;
}
break;
case -937446323:
if(name.equals("ImageButton")) {
var12 = 5;
}
break;
case -658531749:
if(name.equals("SeekBar")) {
var12 = 12;
}
break;
case -339785223:
if(name.equals("Spinner")) {
var12 = 4;
}
break;
case 776382189:
if(name.equals("RadioButton")) {
var12 = 7;
}
break;
case 1125864064:
if(name.equals("ImageView")) {
var12 = 1;
}
break;
case 1413872058:
if(name.equals("AutoCompleteTextView")) {
var12 = 9;
}
break;
case 1601505219:
if(name.equals("CheckBox")) {
var12 = 6;
}
break;
case 1666676343:
if(name.equals("EditText")) {
var12 = 3;
}
break;
case 2001146706:
if(name.equals("Button")) {
var12 = 2;
}
}
switch(var12) {
case 0:
view = new AppCompatTextView(context, attrs);
break;
case 1:
view = new AppCompatImageView(context, attrs);
break;
case 2:
view = new AppCompatButton(context, attrs);
break;
case 3:
view = new AppCompatEditText(context, attrs);
break;
case 4:
view = new AppCompatSpinner(context, attrs);
break;
case 5:
view = new AppCompatImageButton(context, attrs);
break;
case 6:
view = new AppCompatCheckBox(context, attrs);
break;
case 7:
view = new AppCompatRadioButton(context, attrs);
break;
case 8:
view = new AppCompatCheckedTextView(context, attrs);
break;
case 9:
view = new AppCompatAutoCompleteTextView(context, attrs);
break;
case 10:
view = new AppCompatMultiAutoCompleteTextView(context, attrs);
break;
case 11:
view = new AppCompatRatingBar(context, attrs);
break;
case 12:
view = new AppCompatSeekBar(context, attrs);
}
if(view == null && context != context) {
view = this.createViewFromTag(context, name, attrs);
}
if(view != null) {
this.checkOnClickListener((View)view, attrs);
}
return (View)view;
}
会发现这里将其实就是将一些低版本的Widget自动变成兼容的Widget（例如将 TextView 变成 AppCompatTextView）以便于向下兼容新版本中的效果，在高版本中的一些Widget新特性就是这样在老版本中也能展示的。
综上，我们完全也可以仿照这种实现方式，将我们需要转变的View转换成我们自定义的View。但是这里我们需要注意一点。
public void setFactory2(Factory2 factory) {
//如果设置过，再设置会抛异常
if (mFactorySet) {
throw new IllegalStateException("A factory has already been set on this LayoutInflater");
}
if (factory == null) {
throw new NullPointerException("Given factory can not be null");
}
//一旦设置过，就会置true
mFactorySet = true;
if (mFactory == null) {
mFactory = mFactory2 = factory;
} else {
mFactory = mFactory2 = new FactoryMerger(factory, factory, mFactory, mFactory2);
}
}
可以看到这里的set方法，原则上是只允许设置一次的，设置过后，就会将mFactorySet变量设置为true,如果再次设置就会抛异常。所以这里当我们的Activity继承的是刚才提到的AppCompatActivity。通过刚才的源码我们发现，在AppCompatActivity的onCreate方法里源码会自动设置一个Factory用于替换Widget向下兼容。所以当我们这时需要自己定义Factory的时候，我们就需要注意需要在super.onCreate()方法之前设置，不然会报异常（反射想干啥干啥...）
FragmentActivity的源码解析
这里还要分析一下FragmentActivity，使用过Fragment的都知道，我们需要将Activity继承FragmentActivity，这是为什么呢？待我们来慢慢分析。
<fragment
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
首先我们知道，Fragment是可以使用标签在XML中定义的，所以我们可以从这个角度考虑一下，看过上一篇博客的应该清楚，在解析XML的时候，特殊的标签都会有专门的条件判断进行解析，例如merge，但是却没有Fragment标签，结合前面的分析，我们这时候应该就该明白，其实也是这个Factory捣的鬼，所以对应于需要继承FragmentActivity，我们这时候就需要去看一下FragmentActivity的源码。通过继承关系我们会发现最终在父类Activity实现了Factory2接口。
继承关系
final FragmentController mFragments = FragmentController.createController(new HostCallbacks());
@Nullable
public View onCreateView(String name, Context context, AttributeSet attrs) {
return null;
}
public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
if (!"fragment".equals(name)) {
return onCreateView(name, context, attrs);
}
return mFragments.onCreateView(parent, name, context, attrs);
}
可以看到这里对fragment进行了特殊的判断，当时Fragment标签时，会交给FragmentController进行创建，而这个FragmentController可以看到在声明变量的时候已经创建了。
private FragmentController(FragmentHostCallback<?> callbacks) {
mHost = callbacks;
}
public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
return mHost.mFragmentManager.onCreateView(parent, name, context, attrs);
}
而且可以看到这里最终会交给一个叫mFragmentManager的onCreateView方法，这里其实已经很熟悉了，但是我们还是来看一看，可以看到这里mHost变量是在构造函数的时候传入的，而前面构造函数可以看到直接new了一个HostCallbacks()，而HostCallbacks是Activity的内部类，继承于FragmentHostCallback。
public abstract class FragmentHostCallback<E> extends FragmentContainer {
...
final FragmentManagerImpl mFragmentManager = new FragmentManagerImpl();
inal class FragmentManagerImpl extends FragmentManager implements LayoutInflater.Factory2 {
@Override
public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
if (!"fragment".equals(name)) {
return null;
}
String fname = attrs.getAttributeValue(null, "class");
TypedArray a =
context.obtainStyledAttributes(attrs, com.android.internal.R.styleable.Fragment);
if (fname == null) {
fname = a.getString(com.android.internal.R.styleable.Fragment_name);
}
int id = a.getResourceId(com.android.internal.R.styleable.Fragment_id, View.NO_ID);
String tag = a.getString(com.android.internal.R.styleable.Fragment_tag);
a.recycle();
int containerId = parent != null ? parent.getId() : 0;
if (containerId == View.NO_ID && id == View.NO_ID && tag == null) {
throw new IllegalArgumentException(attrs.getPositionDescription()
+ ": Must specify unique android:id, android:tag, or have a parent with"
+ " an id for " + fname);
}
// If we restored from a previous state, we may already have
// instantiated this fragment from the state and should use
// that instance instead of making a new one.
//先查找已存在的Fragment
Fragment fragment = id != View.NO_ID ? findFragmentById(id) : null;
if (fragment == null && tag != null) {
fragment = findFragmentByTag(tag);
}
if (fragment == null && containerId != View.NO_ID) {
fragment = findFragmentById(containerId);
}
if (FragmentManagerImpl.DEBUG) Log.v(TAG, "onCreateView: id=0x"
+ Integer.toHexString(id) + " fname=" + fname
+ " existing=" + fragment);
if (fragment == null) {
//反射创建
fragment = mContainer.instantiate(context, fname, null);
fragment.mFromLayout = true;
fragment.mFragmentId = id != 0 ? id : containerId;
fragment.mContainerId = containerId;
fragment.mTag = tag;
fragment.mInLayout = true;
fragment.mFragmentManager = this;
fragment.mHost = mHost;
fragment.onInflate(mHost.getContext(), attrs, fragment.mSavedFragmentState);
addFragment(fragment, true);
} else if (fragment.mInLayout) {
// A fragment already exists and it is not one we restored from
// previous state.
throw new IllegalArgumentException(attrs.getPositionDescription()
+ ": Duplicate id 0x" + Integer.toHexString(id)
+ ", tag " + tag + ", or parent id 0x" + Integer.toHexString(containerId)
+ " with another fragment for " + fname);
} else {
// This fragment was retained from a previous instance; get it
// going now.
fragment.mInLayout = true;
fragment.mHost = mHost;
// If this fragment is newly instantiated (either right now, or
// from last saved state), then give it the attributes to
// initialize itself.
if (!fragment.mRetaining) {
fragment.onInflate(mHost.getContext(), attrs, fragment.mSavedFragmentState);
}
}
// If we haven't finished entering the CREATED state ourselves yet,
// push the inflated child fragment along. This will ensureInflatedFragmentView
// at the right phase of the lifecycle so that we will have mView populated
// for compliant fragments below.
if (mCurState < Fragment.CREATED && fragment.mFromLayout) {
//回调Fragment的onCreateView生命周期
moveToState(fragment, Fragment.CREATED, 0, 0, false);
} else {
moveToState(fragment);
}
if (fragment.mView == null) {
throw new IllegalStateException("Fragment " + fname
+ " did not create a view.");
}
if (id != 0) {
fragment.mView.setId(id);
}
if (fragment.mView.getTag() == null) {
fragment.mView.setTag(tag);
}
return fragment.mView;
}
}
}
到这里就很清楚了，这里首先查找已存在的Fragment，如果没有找到就利用反射创建Fragment的实例。
void moveToState(Fragment f, int newState, int transit, int transitionStyle,
boolean keepActive) {
switch (f.mState) {
case Fragment.CREATED:
f.mView = f.performCreateView(f.performGetLayoutInflater(
f.mSavedFragmentState), container, f.mSavedFragmentState);
...
}
}
public class Fragment implements Parcelable{
View performCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (mChildFragmentManager != null) {
mChildFragmentManager.noteStateNotSaved();
}
mPerformedCreateView = true;
//回调生命周期
return onCreateView(inflater, container, savedInstanceState);
}
}
总结
通过上面的分析我们其实会发现Factory的强大之处，利用Factory我们可以做许多的操作，例如更换主题等。经过这两篇博客的分析，对于LayoutInflater我们算是有了一个比较全面的了解，只能说对于View，我们需要了解的还有很多。
