遇见LayoutInflater&Factory
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2022-06-15 14:16:00
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LayoutInflater的获取
在我们写listview的adapter的getView方法中我们都会通过LayoutInflater.from(mContext)获取LayoutInflater实例。
现在我们通过源码来分析一下LayoutInflater实例的获取：
//LayoutInflater的获取
public abstract class LayoutInflater {
/**
* Obtains the LayoutInflater from the given context.
*/
public static LayoutInflater from(Context context) {
LayoutInflater LayoutInflater =
(LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (LayoutInflater == null) {
throw new AssertionError("LayoutInflater not found.");
}
return LayoutInflater;
}
}context.getSystemService 是Android很重要的一个API，它是Activity的一个方法，根据传入的NAME来取得对应的Object，然后转换成相应的服务对象。以下介绍系统相应的服务。
| Name | 返回的对象 | 说明 |
|---|---|---|
| WINDOW_SERVICE | WindowManager | 管理打开的窗口程序 |
| LAYOUT_INFLATER_SERVICE | LayoutInflater | 取得xml里定义的view |
| ACTIVITY_SERVICE | ActivityManager | 管理应用程序的系统状态 |
| POWER_SERVICE | PowerManger | 电源的服务 |
| ALARM_SERVICE | AlarmManager | 闹钟的服务 |
| NOTIFICATION_SERVICE | NotificationManager | 状态栏的服务 |
| KEYGUARD_SERVICE | KeyguardManager | 键盘锁的服务 |
| LOCATION_SERVICE | LocationManager | 位置的服务，如GPS |
| SEARCH_SERVICE | SearchManager | 搜索的服务 |
| VEBRATOR_SERVICE | Vebrator | 手机震动的服务 |
| CONNECTIVITY_SERVICE | Connectivity | 网络连接的服务 |
| WIFI_SERVICE | WifiManager | Wi-Fi服务 |
| TELEPHONY_SERVICE | TeleponyManager | 电话服务 |
获取LayoutInflater服务
class ContextImpl extends Context {
/***部分代码省略****/
static {
/***部分代码省略****/
registerService(LAYOUT_INFLATER_SERVICE, new ServiceFetcher() {
public Object createService(ContextImpl ctx) {
return PolicyManager.makeNewLayoutInflater(ctx.getOuterContext());
}});
/***部分代码省略****/
}
/***部分代码省略****/
}从源码可以看出LayoutInflater实例是由 PolicyManager.makeNewLayoutInflater 获取的，PolicyManager有没有感觉很熟悉。上一章 Activity中的Window的setContentView 中我们获取Activity中的Window的实例的时候就是通过PolicyManager获取的，我们进一步往下跟进。
public final class PolicyManager {
private static final String POLICY_IMPL_CLASS_NAME =
"com.android.internal.policy.impl.Policy";
private static final IPolicy sPolicy;
static {
// Pull in the actual implementation of the policy at run-time
try {
Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
sPolicy = (IPolicy)policyClass.newInstance();
} catch (ClassNotFoundException ex) {
throw new RuntimeException(
POLICY_IMPL_CLASS_NAME + " could not be loaded", ex);
} catch (InstantiationException ex) {
throw new RuntimeException(
POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
} catch (IllegalAccessException ex) {
throw new RuntimeException(
POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
}
}
/***部分代码省略****/
public static LayoutInflater makeNewLayoutInflater(Context context) {
//反射获取实例
return sPolicy.makeNewLayoutInflater(context);
}
}
public class Policy implements IPolicy {
/***部分代码省略****/
public LayoutInflater makeNewLayoutInflater(Context context) {
//LayoutInflater的最终实例
return new PhoneLayoutInflater(context);
}
/***部分代码省略****/
}PhoneLayoutInflater的实现
public class PhoneLayoutInflater extends LayoutInflater {
private static final String[] sClassPrefixList = {
"android.widget.",
"android.webkit.",
"android.app."
};
public PhoneLayoutInflater(Context context) {
super(context);
}
protected PhoneLayoutInflater(LayoutInflater original, Context newContext) {
super(original, newContext);
}
/** Override onCreateView to instantiate names that correspond to the
widgets known to the Widget factory. If we don't find a match,
call through to our super class.
*/
@Override protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException {
for (String prefix : sClassPrefixList) {
try {
View view = createView(name, prefix, attrs);
if (view != null) {
return view;
}
} catch (ClassNotFoundException e) {
// In this case we want to let the base class take a *****
// at it.
}
}
return super.onCreateView(name, attrs);
}
public LayoutInflater cloneInContext(Context newContext) {
return new PhoneLayoutInflater(this, newContext);
}
}LayoutInflater最常使用的方法
在Android中LayoutInflater中最常使用的情况基本都是调用inflate方法用来构造View对象。
public abstract class LayoutInflater {
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
return inflate(resource, root, root != null);
}
public View inflate(XmlPullParser parser, @Nullable ViewGroup root) {
return inflate(parser, root, root != null);
}
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
final Resources res = getContext().getResources();
if (DEBUG) {
Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" ("
+ Integer.toHexString(resource) + ")");
}
final XmlResourceParser parser = res.getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}
/**
* @param parser xml数据结构
* @param root 一个可依附的rootview
* @param attachToRoot 是否将parser解析生产的View添加在root上
*/
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");
//当前上下文环境
final Context inflaterContext = mContext;
//所有的属性集合获取类
final AttributeSet attrs = Xml.asAttributeSet(parser);
Context lastContext = (Context) mConstructorArgs[0];
mConstructorArgs[0] = inflaterContext;
//根节点
View result = root;
try {
// Look for the root node.寻找根节点
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
// Empty
}
//找不到根节点抛出异常
if (type != XmlPullParser.START_TAG) {
throw new InflateException(parser.getPositionDescription()
+ ": No start tag found!");
}
final String name = parser.getName();
if (DEBUG) {
System.out.println("**************************");
System.out.println("Creating root view: "
+ name);
System.out.println("**************************");
}
//merge标签解析
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");
}
//递归调用，添加root的孩子节点
rInflate(parser, root, inflaterContext, attrs, false);
} else {
// Temp is the root view that was found in the xml。根据当前的attrs和xml创建一个xml根view
final View temp = createViewFromTag(root, name, inflaterContext, attrs);
ViewGroup.LayoutParams params = null;
if (root != null) {
if (DEBUG) {
System.out.println("Creating params from root: " +
root);
}
// Create layout params that match root, if supplied。构造LayoutParams
params = root.generateLayoutParams(attrs);
if (!attachToRoot) {
// Set the layout params for temp if we are not
// attaching. (If we are, we use addView, below)
temp.setLayoutParams(params);
}
}
if (DEBUG) {
System.out.println("-----> start inflating children");
}
// Inflate all children under temp against its context.递归调用，添加temp的孩子节点
rInflateChildren(parser, temp, attrs, true);
if (DEBUG) {
System.out.println("-----> done inflating children");
}
// We are supposed to attach all the views we found (int temp)
// to root. Do that now.
if (root != null && attachToRoot) {
//将xml解析出来的viewgroup添加在root的根下
root.addView(temp, params);
}
// Decide whether to return the root that was passed in or the
// top view found in xml.
if (root == null || !attachToRoot) {
result = temp;
}
}
} catch (XmlPullParserException e) {
InflateException ex = new InflateException(e.getMessage());
ex.initCause(e);
throw ex;
} catch (Exception e) {
InflateException ex = new InflateException(
parser.getPositionDescription()
+ ": " + e.getMessage());
ex.initCause(e);
throw ex;
} finally {
// Don't retain static reference on context.
mConstructorArgs[0] = lastContext;
mConstructorArgs[1] = null;
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
return result;
}
}
}这四个重载的inflate方法最终都是通过inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) 进行实现的。
LayoutInflater的使用中重点关注inflate方法的参数含义：
- inflate(xmlId, null); 只创建temp的View，然后直接返回temp。
- inflate(xmlId, parent); 创建temp的View，然后执行root.addView(temp, params);最后返回root。
- inflate(xmlId, parent, false); 创建temp的View，然后执行temp.setLayoutParams(params);然后再返回temp。
- inflate(xmlId, parent, true); 创建temp的View，然后执行root.addView(temp, params);最后返回root。
- inflate(xmlId, null, false); 只创建temp的View，然后直接返回temp。
- inflate(xmlId, null, true); 只创建temp的View，然后直接返回temp。
LayoutInflater解析视图xml
- xml视图树解析
递归执行rInflate生产View并添加给父容器
public abstract class LayoutInflater {
/**
* 将parser解析器中包含的view结合属性标签attrs生产view添加在parent容器中
* @param parser xml解析器
* @param parent 父容器
* @param attrs 属性标签集合
* @param finishInflate 生产view之后是否执行父容器的onFinishInflate方法。
*/
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;
while (((type = parser.next()) != XmlPullParser.END_TAG ||
parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
if (type != XmlPullParser.START_TAG) {
continue;
}
final String name = parser.getName();
if (TAG_REQUEST_FOCUS.equals(name)) { //requestFocus标签解析
parseRequestFocus(parser, parent);
} else if (TAG_TAG.equals(name)) { //tag标签解析
parseViewTag(parser, parent, attrs);
} else if (TAG_INCLUDE.equals(name)) { //include标签解析
if (parser.getDepth() == 0) {
throw new InflateException("<include /> cannot be the root element");
}
parseInclude(parser, context, parent, attrs);
} else if (TAG_MERGE.equals(name)) { //merge标签解析
throw new InflateException("<merge /> must be the root element");
} else {
//View标签解析
final View view = createViewFromTag(parent, name, context, attrs);
final ViewGroup viewGroup = (ViewGroup) parent;
//View所在容器（ViewGroup）的属性解析
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
//循环遍历xml的子节点
rInflateChildren(parser, view, attrs, true);
//将解析出的view和其对于的属性参数添加在父容器中
viewGroup.addView(view, params);
}
}
if (finishInflate) {
parent.onFinishInflate();
}
}
}- 单个View布局的解析
调用createViewFromTag，设置View的Theme属性。再调用CreateView方法创建view
public abstract class LayoutInflater {
protected View onCreateView(String name, AttributeSet attrs)
throws ClassNotFoundException {
return createView(name, "android.view.", attrs);
}
protected View onCreateView(View parent, String name, AttributeSet attrs)
throws ClassNotFoundException {
return onCreateView(name, attrs);
}
/**
* 将parser解析器中包含的view结合属性标签attrs生产view添加在parent容器中
* @param parent 父容器
* @param name view名称
* @param context 上下文环境
* @param attrs 属性标签集合
*/
private View createViewFromTag(View parent, String name, Context context, AttributeSet attrs) {
return createViewFromTag(parent, name, context, attrs, false);
}
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.//应用theme
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();
}
if (name.equals(TAG_1995)) {
// Let's party like it's 1995!
return new BlinkLayout(context, attrs);
}
try {
View view;
/*************************start Factory*/
//使用LayoutInflater的Factory，对View进行修改
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);
}
/*************************end Factory*/
if (view == null) {
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
if (-1 == name.indexOf('.')) {
//创建Android原生的View（android.view包下面的view）
view = onCreateView(parent, name, attrs);
} else {
//创建自定义View或者依赖包中的View（xml中声明的是全路径）
view = createView(name, null, attrs);
}
} finally {
mConstructorArgs[0] = lastContext;
}
}
return view;
} catch (InflateException e) {
throw e;
} catch (ClassNotFoundException e) {
final InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class " + name);
ie.initCause(e);
throw ie;
} catch (Exception e) {
final InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class " + name);
ie.initCause(e);
throw ie;
}
}
public final View createView(String name, String prefix, AttributeSet attrs)
throws ClassNotFoundException, InflateException {
Constructor<? extends View> constructor = sConstructorMap.get(name);
Class<? extends View> clazz = null;
try {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, name);
//判断View的构造是否进行缓存
if (constructor == null) {
// Class not found in the cache, see if it's real, and try to add it
clazz = mContext.getClassLoader().loadClass(
prefix != null ? (prefix + name) : name).asSubclass(View.class);
if (mFilter != null && clazz != null) {
boolean allowed = mFilter.onLoadClass(clazz);
if (!allowed) {
failNotAllowed(name, prefix, attrs);
}
}
//static final Class<?>[] mConstructorSignature = new Class[] {Context.class, AttributeSet.class};
constructor = clazz.getConstructor(mConstructorSignature);
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 = mContext.getClassLoader().loadClass(
prefix != null ? (prefix + name) : name).asSubclass(View.class);
boolean allowed = clazz != null && mFilter.onLoadClass(clazz);
mFilterMap.put(name, allowed);
if (!allowed) {
failNotAllowed(name, prefix, attrs);
}
} else if (allowedState.equals(Boolean.FALSE)) {
failNotAllowed(name, prefix, attrs);
}
}
}
Object[] args = mConstructorArgs;
args[1] = attrs;
constructor.setAccessible(true);
//读取View的构造函数，传入context、attrs作为参数。View(Context context, AttributeSet attrs)；
final View view = constructor.newInstance(args);
//处理ViewStub标签
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;
} catch (NoSuchMethodException e) {
InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class "
+ (prefix != null ? (prefix + name) : name));
ie.initCause(e);
throw ie;
} catch (ClassCastException e) {
// If loaded class is not a View subclass
InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Class is not a View "
+ (prefix != null ? (prefix + name) : name));
ie.initCause(e);
throw ie;
} catch (ClassNotFoundException e) {
// If loadClass fails, we should propagate the exception.
throw e;
} catch (Exception e) {
InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class "
+ (clazz == null ? "<unknown>" : clazz.getName()));
ie.initCause(e);
throw ie;
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
}LayoutInflater创建View的总结
- 在inflate方法中，通过Resource.getLayout(resource)生产XmlResourceParser对象；
- 利用该对象实例生产XmlPullAttributes以便于xml标签中的属性。然后将这个两个对象传递到rInflate方法中，解析layout对应的xml文件；
- 接着将（父容器、xml中View的名称、属性标签）传递给createViewFromTag方法创建对应的View；
- 在createViewFromTag方法中执行LayoutInflater.Factory或者LayoutInflater的createView方法。
- 在createView方法中我们已知View的类名和View的属性标签集合，通过Java反射执行View的构造方法创建View对象。这也就是为什么我们在自定义View的时候必须复写View的构造函数View(Context context, AttributeSet attrs)；
LayoutInflater.Factory简介
LayoutInflater.Factory这个类在我们开发的过程中很少越到。但是我们在查看LayoutInflater解析View源码的过程中可以看到如果LayoutInflater中有mFactory这个实例那么可以通过mFactory创建View,同时也能修改入参AttributeSet属性值。
public abstract class LayoutInflater {
/***部分代码省略****/
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);
}
/***部分代码省略****/
}- LayoutInflater有两个工厂类，Factory和Factory2，区别只是在于Factory2可以传入父容器作为参数。
public abstract class LayoutInflater {
/***部分代码省略****/
public void setFactory(Factory factory) {
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");
}
mFactorySet = true;
if (mFactory == null) {
mFactory = factory;
} else {
mFactory = new FactoryMerger(factory, null, mFactory, mFactory2);
}
}
public void setFactory2(Factory2 factory) {
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");
}
mFactorySet = true;
if (mFactory == null) {
mFactory = mFactory2 = factory;
} else {
mFactory = mFactory2 = new FactoryMerger(factory, factory, mFactory, mFactory2);
}
}
/***部分代码省略****/
}这两个方法的功能基本是一致的，setFactory2是在Android3.0之后以后引入的，所以我们要根据SDK的版本去选择调用上述方法。
在supportv4下边也有LayoutInflaterCompat可以做相同的操作。
public class LayoutInflaterCompat {
/***部分代码省略****/
static final LayoutInflaterCompatImpl IMPL;
static {
final int version = Build.VERSION.SDK_INT;
if (version >= 21) {
IMPL = new LayoutInflaterCompatImplV21();
} else if (version >= 11) {
IMPL = new LayoutInflaterCompatImplV11();
} else {
IMPL = new LayoutInflaterCompatImplBase();
}
}
private LayoutInflaterCompat() {
}
public static void setFactory(LayoutInflater inflater, LayoutInflaterFactory factory) {
IMPL.setFactory(inflater, factory);
}
}LayoutInflater.Factory的使用
找到当前Activity中的id=R.id.text的TextView将其替换为Button，并修改BackgroundColor。
public class MainActivity extends Activity {
final String TAG = "MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
LayoutInflater.from(this).setFactory(new LayoutInflater.Factory() {
@Override
public View onCreateView(String name, Context context, AttributeSet attrs) {
if ("TextView".equals(name)) {
Log.e(TAG, "name = " + name);
int n = attrs.getAttributeCount();
//打印所有属性标签
for (int i = 0; i < n; i++) {
Log.e(TAG, attrs.getAttributeName(i) + " , " + attrs.getAttributeValue(i));
}
for (int i = 0; i < n; i++) {
if (attrs.getAttributeName(i).equals("id")) {
String attributeValue = attrs.getAttributeValue(i);
String id = attributeValue.substring(1, attributeValue.length());
if (R.id.text == Integer.valueOf(id)) {
Button button = new Button(context, attrs);
button.setBackgroundColor(Color.RED);
return button;
}
}
}
}
return null;
}
});
setContentView(R.layout.activity_main);
}
}Console输出：
MainActivity: name = TextView
MainActivity: id , @2131492944
MainActivity: layout_width , -2
MainActivity: layout_height , -2
MainActivity: text , Hello World!是不是发现LayoutInflater的Factory功能很好很强大。
这里提一个问题，如果把上面代码中的MainActivity的父类修改为AppCompatActivity会怎么样呢？我们试着运行一下。
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.example.tzx.dexload/com.example.tzx.dexload.MainActivity}:
java.lang.IllegalStateException: A factory has already been set on this LayoutInflater程序运行报错:A factory has already been set on this LayoutInflater。这个是在执行LayoutInflater的setFactory方法时抛出的异常。因为mFactorySet=true。。。。这个时候我们发现LayoutInflater的Factory已经被设置过了。具体是在哪里设置的呢？我们看看下边LayoutInflater.Factory在Android源码中的使用部分内容。
LayoutInflater.Factory在Android源码中的使用
在我们开发过程是很少使用到LayoutInflater.Factory，但是Android在supportv7中就使用，我们来学习一下。
在AppComPatActivity中的onCreate就进行了LayoutInflater.Factory的设置。
public class AppCompatActivity extends FragmentActivity implements AppCompatCallback,
TaskStackBuilder.SupportParentable, ActionBarDrawerToggle.DelegateProvider {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
getDelegate().installViewFactory();
getDelegate().onCreate(savedInstanceState);
super.onCreate(savedInstanceState);
}
public AppCompatDelegate getDelegate() {
if (mDelegate == null) {
mDelegate = AppCompatDelegate.create(this, this);
}
return mDelegate;
}
}- 根据不通的sdk版本做适配
public abstract class AppCompatDelegate {
public static AppCompatDelegate create(Activity activity, AppCompatCallback callback) {
return create(activity, activity.getWindow(), callback);
}
/***部分代码省略****/
//对于不同的版本做适配
private static AppCompatDelegate create(Context context, Window window,
AppCompatCallback callback) {
final int sdk = Build.VERSION.SDK_INT;
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 AppCompatDelegateImplV7(context, window, callback);
}
}
}LayoutInflaterFactory的实现类，以及触发LayoutInflater.setFactory的调用。
class AppCompatDelegateImplV7 extends AppCompatDelegateImplBase
implements MenuBuilder.Callback, LayoutInflaterFactory {
/***部分代码省略****/
@Override
public void installViewFactory() {
LayoutInflater layoutInflater = LayoutInflater.from(mContext);
if (layoutInflater.getFactory() == null) {
//进行setFactory的设置
LayoutInflaterCompat.setFactory(layoutInflater, this);
} else {
Log.i(TAG, "The Activity's LayoutInflater already has a Factory installed"
+ " so we can not install AppCompat's");
}
}
/***部分代码省略****/
@Override
public View createView(View parent, final String name, @NonNull Context context,
@NonNull AttributeSet attrs) {
final boolean isPre21 = Build.VERSION.SDK_INT < 21;
if (mAppCompatViewInflater == null) {
//具体的实现类，下文会有讲到
mAppCompatViewInflater = new AppCompatViewInflater();
}
// We only want the View to inherit it's context if we're running pre-v21
final boolean inheritContext = isPre21 && mSubDecorInstalled
&& shouldInheritContext((ViewParent) parent);
return mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext,
isPre21, /* Only read android:theme pre-L (L+ handles this anyway) */
true /* Read read app:theme as a fallback at all times for legacy reasons */
);
}
}- 根据不同的版本找到LayoutInflater的包装类
public final class LayoutInflaterCompat {
interface LayoutInflaterCompatImpl {
public void setFactory(LayoutInflater layoutInflater, LayoutInflaterFactory factory);
public LayoutInflaterFactory getFactory(LayoutInflater layoutInflater);
}
static class LayoutInflaterCompatImplBase implements LayoutInflaterCompatImpl {
@Override
public void setFactory(LayoutInflater layoutInflater, LayoutInflaterFactory factory) {
LayoutInflaterCompatBase.setFactory(layoutInflater, factory);
}
@Override
public LayoutInflaterFactory getFactory(LayoutInflater layoutInflater) {
return LayoutInflaterCompatBase.getFactory(layoutInflater);
}
}
static final LayoutInflaterCompatImpl IMPL;
static {
final int version = Build.VERSION.SDK_INT;
if (version >= 21) {
IMPL = new LayoutInflaterCompatImplV21();
} else if (version >= 11) {
IMPL = new LayoutInflaterCompatImplV11();
} else {
IMPL = new LayoutInflaterCompatImplBase();
}
}
/***部分代码省略****/
private LayoutInflaterCompat() {
}
public static void setFactory(LayoutInflater inflater, LayoutInflaterFactory factory) {
IMPL.setFactory(inflater, factory);
}
public static LayoutInflaterFactory getFactory(LayoutInflater inflater) {
return IMPL.getFactory(inflater);
}
}- FactoryWrapper类通过调用LayoutInflaterFactory的onCreateView方法，实现了LayoutInflater.Factory接口。最终调用了LayoutInflater的setFactory方法，使得在LayoutInflater.createViewFromTag中创建View的时候通过Factory进行床架。
public interface LayoutInflaterFactory {
public View onCreateView(View parent, String name, Context context, AttributeSet attrs);
}
class LayoutInflaterCompatBase {
static class FactoryWrapper implements LayoutInflater.Factory {
final LayoutInflaterFactory mDelegateFactory;
FactoryWrapper(LayoutInflaterFactory delegateFactory) {
mDelegateFactory = delegateFactory;
}
@Override
public View onCreateView(String name, Context context, AttributeSet attrs) {
//调用LayoutInflaterFactory实现类的onCreateView(null, name, context, attrs)方法
return mDelegateFactory.onCreateView(null, name, context, attrs);
}
public String toString() {
return getClass().getName() + "{" + mDelegateFactory + "}";
}
}
static void setFactory(LayoutInflater inflater, LayoutInflaterFactory factory) {
//最终调用了LayoutInflater的setFactory方法，对Factory进行设置
inflater.setFactory(factory != null ? new FactoryWrapper(factory) : null);
}
static LayoutInflaterFactory getFactory(LayoutInflater inflater) {
LayoutInflater.Factory factory = inflater.getFactory();
if (factory instanceof FactoryWrapper) {
return ((FactoryWrapper) factory).mDelegateFactory;
}
return null;
}
}- 在LayoutInflaterFactory的实现类之一AppCompatDelegateImplV7中，找到了setFactory的实际使用意义实际意思。
- 在LayoutInflater.createViewFromTag方法中调用
Factory.onCreateView(name, context, attrs)方法
- Factory的实现类FactoryWrapper中，调用
LayoutInflaterFactory的onCreateView(null, name, context, attrs)方法
- 在LayoutInflater.createViewFromTag方法中调用
class AppCompatViewInflater {
/***部分代码省略****/
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;
// We can emulate Lollipop's android:theme attribute propagating down the view hierarchy
// by using the parent's context
if (inheritContext && parent != null) {
context = parent.getContext();
}
if (readAndroidTheme || readAppTheme) {
// We then apply the theme on the context, if specified
context = themifyContext(context, attrs, readAndroidTheme, readAppTheme);
}
if (wrapContext) {
context = TintContextWrapper.wrap(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) {
// If the original context does not equal our themed context, then we need to manually
// inflate it using the name so that android:theme takes effect.
view = createViewFromTag(context, name, attrs);
}
if (view != null) {
// If we have created a view, check it's android:onClick
checkOnClickListener(view, attrs);
}
return view;
}
}- AppCompatViewInflater作为LayoutInflaterFactory的的onCreateView方法的最终实现类，通过createView方法替换了一些我们想要自己替换的View。比如：
| 原始View | 实际创建的View |
|---|---|
| TextView | AppCompatTextView |
| ImageView | AppCompatImageView |
| Button | AppCompatButton |
| …… | …… |
在appcompat使用自定义的LayoutInflater.Factory
这里我们有两种书写方式：
- 继续使用 LayoutInflater.from(this).setFactory 方法。
LayoutInflater.from(this).setFactory(new LayoutInflater.Factory() {
@Override
public View onCreateView(String name, Context context, AttributeSet attrs) {
AppCompatDelegate delegate = getDelegate();
//调用AppCompatDelegate的createView方法将第一个参数设置为null
View view = delegate.createView(null, name, context, attrs);
if ("TextView".equals(name)) {
Log.e(TAG, "name = " + name);
int n = attrs.getAttributeCount();
for (int i = 0; i < n; i++) {
Log.e(TAG, attrs.getAttributeName(i) + " , " + attrs.getAttributeValue(i));
}
for (int i = 0; i < n; i++) {
if (attrs.getAttributeName(i).equals("id")) {
String attributeValue = attrs.getAttributeValue(i);
String id = attributeValue.substring(1, attributeValue.length());
if (R.id.text == Integer.valueOf(id)) {
Button button = new Button(context, attrs);
button.setBackgroundColor(Color.RED);
button.setAllCaps(false);
return button;
}
}
}
}
return view;
}
});- 使用LayoutInflaterCompat.setFactory方法
LayoutInflaterCompat.setFactory(LayoutInflater.from(this), new LayoutInflaterFactory() {
@Override
public View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
//appcompat 创建view代码
AppCompatDelegate delegate = getDelegate();
View view = delegate.createView(parent, name, context, attrs);
if ("TextView".equals(name)) {
Log.e(TAG, "name = " + name);
int n = attrs.getAttributeCount();
for (int i = 0; i < n; i++) {
Log.e(TAG, attrs.getAttributeName(i) + " , " + attrs.getAttributeValue(i));
}
for (int i = 0; i < n; i++) {
if (attrs.getAttributeName(i).equals("id")) {
String attributeValue = attrs.getAttributeValue(i);
String id = attributeValue.substring(1, attributeValue.length());
if (R.id.text == Integer.valueOf(id)) {
Button button = new Button(context, attrs);
button.setBackgroundColor(Color.RED);
button.setAllCaps(false);
return button;
}
}
}
}
return view;
}
});两种写法的原理是相同的，因为上面讲述的LayoutInflater.Factory的实现类FactoryWrapper实现onCreateView方法的时候调用的AppCompatDelegate.onCreateView的时候第一个参数传递的值就是null。
Android应用中的换肤（夜间模式）是不是也利用的是LayoutInflater.Factory原理实现的呢，我们一起期待下一篇关于Android换肤文章。
参考文章：
Android 探究 LayoutInflater setFactory
文章到这里就全部讲述完啦，若有其他需要交流的可以留言哦~！~！
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