LayoutInflater的擷取
在我們寫listview的adapter的getView方法中我們都會通過
LayoutInflater.from(mContext)
擷取LayoutInflater執行個體。
現在我們通過源碼來分析一下LayoutInflater執行個體的擷取：
//LayoutInflater的擷取
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很重要的一個API，它是Activity的一個方法，根據傳入的NAME來取得對應的Object，然後轉換成相應的服務對象。以下介紹系統相應的服務。
| Name | 傳回的對象 | 說明 |
| WINDOW_SERVICE | WindowManager | 管理打開的視窗程式 |
| LAYOUT_INFLATER_SERVICE | LayoutInflater | 取得xml裡定義的view |
| ACTIVITY_SERVICE | ActivityManager | 管理應用程式的系統狀态 |
| POWER_SERVICE | PowerManger | 電源的服務 |
| ALARM_SERVICE | AlarmManager | 鬧鐘的服務 |
| NOTIFICATION_SERVICE | NotificationManager | 狀态欄的服務 |
| KEYGUARD_SERVICE | KeyguardManager | 鍵盤鎖的服務 |
| LOCATION_SERVICE | LocationManager | 位置的服務，如GPS |
| SEARCH_SERVICE | SearchManager | 搜尋的服務 |
| VEBRATOR_SERVICE | Vebrator | 手機震動的服務 |
| CONNECTIVITY_SERVICE | Connectivity | 網絡連接配接的服務 |
| WIFI_SERVICE | WifiManager | Wi-Fi服務 |
| TELEPHONY_SERVICE | TeleponyManager | 電話服務 |
擷取LayoutInflater服務
class ContextImpl extends Context {
/***部分代碼省略****/
static {
/***部分代碼省略****/
registerService(LAYOUT_INFLATER_SERVICE, new ServiceFetcher() {
public Object createService(ContextImpl ctx) {
return PolicyManager.makeNewLayoutInflater(ctx.getOuterContext());
}});
/***部分代碼省略****/
}
/***部分代碼省略****/
} 從源碼可以看出LayoutInflater執行個體是由
PolicyManager.makeNewLayoutInflater
擷取的，PolicyManager有沒有感覺很熟悉。上一章 Activity中的Window的setContentView 中我們擷取Activity中的Window的執行個體的時候就是通過PolicyManager擷取的，我們進一步往下跟進。
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);
}
}
/***部分代碼省略****/
public static LayoutInflater makeNewLayoutInflater(Context context) {
//反射擷取執行個體
return sPolicy.makeNewLayoutInflater(context);
}
}
public class Policy implements IPolicy {
/***部分代碼省略****/
public LayoutInflater makeNewLayoutInflater(Context context) {
//LayoutInflater的最終執行個體
return new PhoneLayoutInflater(context);
}
/***部分代碼省略****/
} PhoneLayoutInflater的實作
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 crack
// 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中最常使用的情況基本都是調用inflate方法用來構造View對象。
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資料結構
* @param root 一個可依附的rootview
* @param attachToRoot 是否将parser解析生産的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");
//目前上下文環境
final Context inflaterContext = mContext;
//所有的屬性集合擷取類
final AttributeSet attrs = Xml.asAttributeSet(parser);
Context lastContext = (Context) mConstructorArgs[0];
mConstructorArgs[0] = inflaterContext;
//根節點
View result = root;
try {
// Look for the root node.尋找根節點
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
// Empty
}
//找不到根節點抛出異常
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标簽解析
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");
}
//遞歸調用，添加root的孩子節點
rInflate(parser, root, inflaterContext, attrs, false);
} else {
// Temp is the root view that was found in the xml。根據目前的attrs和xml建立一個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。構造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.遞歸調用，添加temp的孩子節點
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解析出來的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;
}
}
} 這四個重載的inflate方法最終都是通過
inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot)
進行實作的。
LayoutInflater的使用中重點關注inflate方法的參數含義：
- inflate(xmlId, null); 隻建立temp的View，然後直接傳回temp。
- inflate(xmlId, parent); 建立temp的View，然後執行root.addView(temp, params);最後傳回root。
- inflate(xmlId, parent, false); 建立temp的View，然後執行temp.setLayoutParams(params);然後再傳回temp。
- inflate(xmlId, parent, true); 建立temp的View，然後執行root.addView(temp, params);最後傳回root。
- inflate(xmlId, null, false); 隻建立temp的View，然後直接傳回temp。
- inflate(xmlId, null, true); 隻建立temp的View，然後直接傳回temp。
LayoutInflater解析視圖xml
-
xml視圖樹解析
遞歸執行rInflate生産View并添加給父容器
public abstract class LayoutInflater {
/**
* 将parser解析器中包含的view結合屬性标簽attrs生産view添加在parent容器中
* @param parser xml解析器
* @param parent 父容器
* @param attrs 屬性标簽集合
* @param finishInflate 生産view之後是否執行父容器的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标簽解析
parseRequestFocus(parser, parent);
} else if (TAG_TAG.equals(name)) { //tag标簽解析
parseViewTag(parser, parent, attrs);
} else if (TAG_INCLUDE.equals(name)) { //include标簽解析
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标簽解析
throw new InflateException("<merge /> must be the root element");
} else {
//View标簽解析
final View view = createViewFromTag(parent, name, context, attrs);
final ViewGroup viewGroup = (ViewGroup) parent;
//View所在容器（ViewGroup）的屬性解析
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
//循環周遊xml的子節點
rInflateChildren(parser, view, attrs, true);
//将解析出的view和其對于的屬性參數添加在父容器中
viewGroup.addView(view, params);
}
}
if (finishInflate) {
parent.onFinishInflate();
}
}
} -
單個View布局的解析
調用createViewFromTag，設定View的Theme屬性。再調用CreateView方法建立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結合屬性标簽attrs生産view添加在parent容器中
* @param parent 父容器
* @param name view名稱
* @param context 上下文環境
* @param attrs 屬性标簽集合
*/
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.//應用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，對View進行修改
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('.')) {
//建立Android原生的View（android.view包下面的view）
view = onCreateView(parent, name, attrs);
} else {
//建立自定義View或者依賴包中的View（xml中聲明的是全路徑）
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);
//判斷View的構造是否進行緩存
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);
//讀取View的構造函數，傳入context、attrs作為參數。View(Context context, AttributeSet attrs)；
final View view = constructor.newInstance(args);
//處理ViewStub标簽
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建立View的總結
- 在inflate方法中，通過Resource.getLayout(resource)生産XmlResourceParser對象；
- 利用該對象執行個體生産XmlPullAttributes以便于xml标簽中的屬性。然後将這個兩個對象傳遞到rInflate方法中，解析layout對應的xml檔案；
- 接着将（父容器、xml中View的名稱、屬性标簽）傳遞給createViewFromTag方法建立對應的View；
- 在createViewFromTag方法中執行LayoutInflater.Factory或者LayoutInflater的createView方法。
- 在createView方法中我們已知View的類名和View的屬性标簽集合，通過Java反射執行View的構造方法建立View對象。這也就是為什麼我們在自定義View的時候必須複寫View的構造函數View(Context context, AttributeSet attrs)；
LayoutInflater.Factory簡介
LayoutInflater.Factory這個類在我們開發的過程中很少越到。但是我們在檢視LayoutInflater解析View源碼的過程中可以看到如果LayoutInflater中有mFactory這個執行個體那麼可以通過mFactory建立View,同時也能修改入參AttributeSet屬性值。
public abstract class LayoutInflater {
/***部分代碼省略****/
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);
}
/***部分代碼省略****/
} - LayoutInflater有兩個工廠類，Factory和Factory2，差別隻是在于Factory2可以傳入父容器作為參數。
public abstract class LayoutInflater {
/***部分代碼省略****/
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);
}
}
/***部分代碼省略****/
} 這兩個方法的功能基本是一緻的，setFactory2是在Android3.0之後以後引入的，是以我們要根據SDK的版本去選擇調用上述方法。
在supportv4下邊也有LayoutInflaterCompat可以做相同的操作。
public class LayoutInflaterCompat {
/***部分代碼省略****/
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
找到目前Activity中的id=R.id.text的TextView将其替換為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();
//列印所有屬性标簽
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輸出：
MainActivity: name = TextView
MainActivity: id , @2131492944
MainActivity: layout_width , -2
MainActivity: layout_height , -2
MainActivity: text , Hello World! 是不是發現LayoutInflater的Factory功能很好很強大。
這裡提一個問題，如果把上面代碼中的MainActivity的父類修改為AppCompatActivity會怎麼樣呢？我們試着運作一下。
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 程式運作報錯:
A factory has already been set on this LayoutInflater
。這個是在執行LayoutInflater的setFactory方法時抛出的異常。因為mFactorySet=true。。。。這個時候我們發現LayoutInflater的Factory已經被設定過了。具體是在哪裡設定的呢？我們看看下邊
LayoutInflater.Factory在Android源碼中的使用
部分内容。
LayoutInflater.Factory在Android源碼中的使用
在我們開發過程是很少使用到LayoutInflater.Factory，但是Android在supportv7中就使用，我們來學習一下。
在AppComPatActivity中的onCreate就進行了LayoutInflater.Factory的設定。
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;
}
} - 根據不通的sdk版本做适配
public abstract class AppCompatDelegate {
public static AppCompatDelegate create(Activity activity, AppCompatCallback callback) {
return create(activity, activity.getWindow(), callback);
}
/***部分代碼省略****/
//對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的實作類，以及觸發LayoutInflater.setFactory的調用。
class AppCompatDelegateImplV7 extends AppCompatDelegateImplBase
implements MenuBuilder.Callback, LayoutInflaterFactory {
/***部分代碼省略****/
@Override
public void installViewFactory() {
LayoutInflater layoutInflater = LayoutInflater.from(mContext);
if (layoutInflater.getFactory() == null) {
//進行setFactory的設定
LayoutInflaterCompat.setFactory(layoutInflater, this);
} else {
Log.i(TAG, "The Activity's LayoutInflater already has a Factory installed"
+ " so we can not install AppCompat's");
}
}
/***部分代碼省略****/
@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) {
//具體的實作類，下文會有講到
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 */
);
}
} - 根據不同的版本找到LayoutInflater的包裝類
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();
}
}
/***部分代碼省略****/
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類通過調用LayoutInflaterFactory的onCreateView方法，實作了LayoutInflater.Factory接口。最終調用了LayoutInflater的setFactory方法，使得在LayoutInflater.createViewFromTag中建立View的時候通過Factory進行床架。
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) {
//調用LayoutInflaterFactory實作類的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) {
//最終調用了LayoutInflater的setFactory方法，對Factory進行設定
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的實作類之一AppCompatDelegateImplV7中，找到了setFactory的實際使用意義實際意思。
- 在LayoutInflater.createViewFromTag方法中調用
方法Factory.onCreateView(name, context, attrs)
- Factory的實作類FactoryWrapper中，調用
方法LayoutInflaterFactory的onCreateView(null, name, context, attrs)
class AppCompatViewInflater {
/***部分代碼省略****/
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作為LayoutInflaterFactory的的onCreateView方法的最終實作類，通過createView方法替換了一些我們想要自己替換的View。比如：
| 原始View | 實際建立的View |
| TextView | AppCompatTextView |
| ImageView | AppCompatImageView |
| Button | AppCompatButton |
| …… | …… |
在appcompat使用自定義的LayoutInflater.Factory
這裡我們有兩種書寫方式：
這裡必須寫在 super.oncreate
- 繼續使用 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();
//調用AppCompatDelegate的createView方法将第一個參數設定為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 建立view代碼
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;
}
}); 兩種寫法的原理是相同的，因為上面講述的LayoutInflater.Factory的實作類FactoryWrapper實作onCreateView方法的時候調用的AppCompatDelegate.onCreateView的時候第一個參數傳遞的值就是null。
Android應用中的換膚（夜間模式）是不是也利用的是LayoutInflater.Factory原理實作的呢，我們一起期待下一篇關于Android換膚文章。
參考文章：
Android 探究 LayoutInflater setFactory
文章到這裡就全部講述完啦，若有其他需要交流的可以留言哦！！
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