又來一篇源碼分析文章。講源碼分析文章有的時候很虛，因為我只能講個我看懂的大概流程，所以細節部分可以沒有深入研究，看完之后也只能了解個大概。但個人覺得看源碼更重要的是思路而不是細節。今天來分析下LayoutInflater的源碼。? 之所以分析它是因為我們來常經常使用到它，但往往只知道它是加載view的而不知它具體的實現方法。不多說直接分析。 ### 源碼分析 平常我們使用LayoutInflater最常見的方式如： ~~~ LayoutInflater inflate = LayoutInflater.from(Context context); LayoutInflater inflate = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); ~~~ 這兩種方式實質上是一樣的。看來LayoutInflater.from的源碼： ~~~ 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; } ~~~ 好吧，它就是一個披著context .getSystemService皮的狼。其實就是簡單的封裝了下。平常我們在獲取系統的一些service如獲取傳感器之類的都會用到getSystemService，那么在這里context .getSystemService又是具體怎么實現的。 ## getSystemService 了解這個問題之前我們要清楚，Context是什么，平時我們經常說Context是上下文環境。其實Application，Activity，Service都會存在一個Context。它的具體實現類是ContextImpl。那么直接看ContextImpl： ~~~ @Override public Object getSystemService(String name) { ServiceFetcher fetcher = SYSTEM_SERVICE_MAP.get(name); return fetcher == null ? null : fetcher.getService(this); } ~~~ SYSTEM_SERVICE_MAP是什么。我們繼續看ContextImpl的代碼： ~~~ class ContextImpl extends Context { private final static String TAG = "ContextImpl"; private final static boolean DEBUG = false; /** * Map from package name, to preference name, to cached preferences. */ private static ArrayMap<String, ArrayMap<String, SharedPreferencesImpl>> sSharedPrefs; /** * Override this class when the system service constructor needs a * ContextImpl. Else, use StaticServiceFetcher below. */ /*package*/ static class ServiceFetcher { int mContextCacheIndex = -1; /** * Main entrypoint; only override if you don't need caching. */ public Object getService(ContextImpl ctx) { ArrayList<Object> cache = ctx.mServiceCache; Object service; synchronized (cache) { if (cache.size() == 0) { // Initialize the cache vector on first access. // At this point sNextPerContextServiceCacheIndex // is the number of potential services that are // cached per-Context. for (int i = 0; i < sNextPerContextServiceCacheIndex; i++) { cache.add(null); } } else { service = cache.get(mContextCacheIndex); if (service != null) { return service; } } service = createService(ctx); cache.set(mContextCacheIndex, service); return service; } } /** * Override this to create a new per-Context instance of the * service. getService() will handle locking and caching. */ public Object createService(ContextImpl ctx) { throw new RuntimeException("Not implemented"); } } abstract static class StaticServiceFetcher extends ServiceFetcher { private Object mCachedInstance; @Override public final Object getService(ContextImpl unused) { synchronized (StaticServiceFetcher.this) { Object service = mCachedInstance; if (service != null) { return service; } return mCachedInstance = createStaticService(); } } public abstract Object createStaticService(); } private static final HashMap<String, ServiceFetcher> SYSTEM_SERVICE_MAP = new HashMap<String, ServiceFetcher>(); private static int sNextPerContextServiceCacheIndex = 0; private static void registerService(String serviceName, ServiceFetcher fetcher) { if (!(fetcher instanceof StaticServiceFetcher)) { fetcher.mContextCacheIndex = sNextPerContextServiceCacheIndex++; } SYSTEM_SERVICE_MAP.put(serviceName, fetcher); } static { ………… registerService(LAYOUT_INFLATER_SERVICE, new ServiceFetcher() { public Object createService(ContextImpl ctx) { return PolicyManager.makeNewLayoutInflater(ctx.getOuterContext()); }}); ………… } ~~~ 在虛擬機第一次加載該類時就會注冊各種ServiceFatcher,包括LayoutInflater，這個是在一系列的registerService中實現的。然后將它們存儲在SYSTEM_SERVICE_MAP這個HashMap中，以后要用只需從中獲取，注冊是在靜態代碼塊中進行的，也就是說它只會執行一次，保證實例的唯一性。這可以說是用容器來實現的單例模式。最后通過getSystemService獲取相應的Service。? 我們重點關注到PolicyManager.makeNewLayoutInflate這句代碼，它最終調用的是Policy中的makeNewLayoutInflate方法。 ~~~ public class Policy implements IPolicy { private static final String TAG = "PhonePolicy"; static { // For performance reasons, preload some policy specific classes when // the policy gets loaded. for (String s : preload_classes) { try { Class.forName(s); } catch (ClassNotFoundException ex) { Log.e(TAG, "Could not preload class for phone policy: " + s); } } } public Window makeNewWindow(Context context) { return new PhoneWindow(context); } public LayoutInflater makeNewLayoutInflater(Context context) { return new PhoneLayoutInflater(context); } } ~~~ 在這里看到Window具體實現類是PhoneWindow，LayoutInflater的具體實現是PhoneLayoutInflater。 ## PhoneLayoutInflater 看下PhoneLayoutInflater的代碼。 ~~~ public class PhoneLayoutInflater extends LayoutInflater { private static final String[] sClassPrefixList = { "android.widget.", "android.webkit.", "android.app." }; /** * Instead of instantiating directly, you should retrieve an instance * through {@link Context#getSystemService} * * @param context The Context in which in which to find resources and other * application-specific things. * * @see Context#getSystemService */ 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); } } ~~~ 它重定了onCreateView 方法，其實就是為系統View加上相應的前綴。如TextView讀出的完整路徑會是android.widget.TextView。再調用createView方法，通過類的完整路徑來構造View對象。具體的實現過程我們可以來看看setContentView。 ## setContentView 首先我們來看一幅android的結構圖：?  Acitivity的一個界面中最外層是PhoneWindow，它里面是一個DecorView。它是界面中所有view的根view。它包括兩部分，ActionBar和ContentView，而ContentView就是我們平常接觸最多的，setContentView設置的就是它的內容。而我們在xml中定義的所有view都是顯示在它上面的。? 先來看下PhoneWindow中的setContentView方法。 ~~~ public void setContentView(int layoutResID) { // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window // decor, when theme attributes and the like are crystalized. Do not check the feature // before this happens. if (mContentParent == null) { installDecor(); } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) { mContentParent.removeAllViews(); } if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) { final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID, getContext()); transitionTo(newScene); } else { mLayoutInflater.inflate(layoutResID, mContentParent); } final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); } ~~~ 首先調用的是installDecor方法。從名字中我們就可以猜到，它應該就是加載DecorView。看下代碼： ~~~ private void installDecor() { if (mDecor == null) { mDecor = generateDecor(); mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS); mDecor.setIsRootNamespace(true); if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) { mDecor.postOnAnimation(mInvalidatePanelMenuRunnable); } } if (mContentParent == null) { mContentParent = generateLayout(mDecor); // Set up decor part of UI to ignore fitsSystemWindows if appropriate. mDecor.makeOptionalFitsSystemWindows(); final DecorContentParent decorContentParent = (DecorContentParent) mDecor.findViewById( R.id.decor_content_parent); if (decorContentParent != null) { mDecorContentParent = decorContentParent; mDecorContentParent.setWindowCallback(getCallback()); if (mDecorContentParent.getTitle() == null) { mDecorContentParent.setWindowTitle(mTitle); } final int localFeatures = getLocalFeatures(); for (int i = 0; i < FEATURE_MAX; i++) { if ((localFeatures & (1 << i)) != 0) { mDecorContentParent.initFeature(i); } } mDecorContentParent.setUiOptions(mUiOptions); if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) != 0 || (mIconRes != 0 && !mDecorContentParent.hasIcon())) { mDecorContentParent.setIcon(mIconRes); } else if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) == 0 && mIconRes == 0 && !mDecorContentParent.hasIcon()) { mDecorContentParent.setIcon( getContext().getPackageManager().getDefaultActivityIcon()); mResourcesSetFlags |= FLAG_RESOURCE_SET_ICON_FALLBACK; } if ((mResourcesSetFlags & FLAG_RESOURCE_SET_LOGO) != 0 || (mLogoRes != 0 && !mDecorContentParent.hasLogo())) { mDecorContentParent.setLogo(mLogoRes); } // Invalidate if the panel menu hasn't been created before this. // Panel menu invalidation is deferred avoiding application onCreateOptionsMenu // being called in the middle of onCreate or similar. // A pending invalidation will typically be resolved before the posted message // would run normally in order to satisfy instance state restoration. PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false); if (!isDestroyed() && (st == null || st.menu == null)) { invalidatePanelMenu(FEATURE_ACTION_BAR); } } else { mTitleView = (TextView)findViewById(R.id.title); if (mTitleView != null) { mTitleView.setLayoutDirection(mDecor.getLayoutDirection()); if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) { View titleContainer = findViewById( R.id.title_container); if (titleContainer != null) { titleContainer.setVisibility(View.GONE); } else { mTitleView.setVisibility(View.GONE); } if (mContentParent instanceof FrameLayout) { ((FrameLayout)mContentParent).setForeground(null); } } else { mTitleView.setText(mTitle); } } } if (mDecor.getBackground() == null && mBackgroundFallbackResource != 0) { mDecor.setBackgroundFallback(mBackgroundFallbackResource); } // Only inflate or create a new TransitionManager if the caller hasn't // already set a custom one. if (hasFeature(FEATURE_ACTIVITY_TRANSITIONS)) { if (mTransitionManager == null) { final int transitionRes = getWindowStyle().getResourceId( R.styleable.Window_windowContentTransitionManager, 0); if (transitionRes != 0) { final TransitionInflater inflater = TransitionInflater.from(getContext()); mTransitionManager = inflater.inflateTransitionManager(transitionRes, mContentParent); } else { mTransitionManager = new TransitionManager(); } } mEnterTransition = getTransition(mEnterTransition, null, R.styleable.Window_windowEnterTransition); mReturnTransition = getTransition(mReturnTransition, USE_DEFAULT_TRANSITION, R.styleable.Window_windowReturnTransition); mExitTransition = getTransition(mExitTransition, null, R.styleable.Window_windowExitTransition); mReenterTransition = getTransition(mReenterTransition, USE_DEFAULT_TRANSITION, R.styleable.Window_windowReenterTransition); mSharedElementEnterTransition = getTransition(mSharedElementEnterTransition, null, R.styleable.Window_windowSharedElementEnterTransition); mSharedElementReturnTransition = getTransition(mSharedElementReturnTransition, USE_DEFAULT_TRANSITION, R.styleable.Window_windowSharedElementReturnTransition); mSharedElementExitTransition = getTransition(mSharedElementExitTransition, null, R.styleable.Window_windowSharedElementExitTransition); mSharedElementReenterTransition = getTransition(mSharedElementReenterTransition, USE_DEFAULT_TRANSITION, R.styleable.Window_windowSharedElementReenterTransition); if (mAllowEnterTransitionOverlap == null) { mAllowEnterTransitionOverlap = getWindowStyle().getBoolean( R.styleable.Window_windowAllowEnterTransitionOverlap, true); } if (mAllowReturnTransitionOverlap == null) { mAllowReturnTransitionOverlap = getWindowStyle().getBoolean( R.styleable.Window_windowAllowReturnTransitionOverlap, true); } if (mBackgroundFadeDurationMillis < 0) { mBackgroundFadeDurationMillis = getWindowStyle().getInteger( R.styleable.Window_windowTransitionBackgroundFadeDuration, DEFAULT_BACKGROUND_FADE_DURATION_MS); } if (mSharedElementsUseOverlay == null) { mSharedElementsUseOverlay = getWindowStyle().getBoolean( R.styleable.Window_windowSharedElementsUseOverlay, true); } } } } ~~~ 可以看到這里不僅初始化mContentParent，而且在之前先調用generateDecor();初始化了一個mDecor，mDecor是DecorView對象，為FrameLayout的子類。并通過findViewById進行獲取控件。? generateLayout(mDecor)猜測應該是用來獲取到了我們的ContentView的；具體我們來看下源碼。 ## generateLayout ~~~ protected ViewGroup generateLayout(DecorView decor) { // Apply data from current theme. TypedArray a = getWindowStyle(); //...... //依據主題style設置一堆值進行設置 int layoutResource; int features = getLocalFeatures(); View in = mLayoutInflater.inflate(layoutResource, null); decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); mContentRoot = (ViewGroup) in; ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT); if (contentParent == null) { throw new RuntimeException("Window couldn't find content container view"); } //...... //繼續一堆屬性設置，完事返回contentParent return contentParent; } ~~~ 之前我們設置界面主題（如Notitle）主要有兩種方式，一種是在xml中設置： ~~~ android:theme="@android:style/Theme.Black.NoTitleBar" ~~~ 一種是調用requestFeature。 ~~~ requestWindowFeature(Window.FEATURE_NO_TITLE); ~~~ 第一種方法對應的就是getWindowStyle方法。而第二種就是在getLocalFeatures完成的。這就是為什么requestWindowFeature要寫在setContentView方法之前的原因。? 接著通過mDecor.findViewById傳入R.id.content，返回mDecor（布局）中的id為content的View，就是我們前面說的ContentView。可以看到我們的mDecor是一個FrameLayout，然后會根據theme去選擇系統中的布局文件，將布局文件通過inflate轉化為view，加入到mDecor中；這些布局文件中都包含一個id為content的FrameLayout，將其引用返回給mContentParent。? 等我們的mContentParent有值了以后，再次回到setContentView中，它會調用以下方法。 ~~~ mLayoutInflater.inflate(layoutResID, mContentParent); ~~~ 接下來重點看inflate是如何加載布局的。 ## inflate ~~~ public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) { synchronized (mConstructorArgs) { Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate"); final AttributeSet attrs = Xml.asAttributeSet(parser); Context lastContext = (Context)mConstructorArgs[0]; mConstructorArgs[0] = mContext; View result = root; try { // Look for the root node. int type; while ((type = parser.next()) != XmlPullParser.START_TAG && type != XmlPullParser.END_DOCUMENT) { // Empty } 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("**************************"); } 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, attrs, false, false); } else { // Temp is the root view that was found in the xml final View temp = createViewFromTag(root, name, attrs, false); 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 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 rInflate(parser, temp, attrs, true, 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) { 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 (IOException 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; } } ~~~ 代碼很長，主要分為以下幾步：? 1.解析XML的根標簽。? 2.如果是merge，調用rInflate進行解析。它會把merge所有子view添加到根標簽中。? 3.如果是普通標簽，調用createViewFromTag進行解析。? 4.調用rInflate解析temp根元素下的子view。并添加到temp中。? 最后返回root。? 看下createViewFromTag是如何加載標簽的。 ~~~ View createViewFromTag(View parent, String name, AttributeSet attrs, boolean inheritContext) { if (name.equals("view")) { name = attrs.getAttributeValue(null, "class"); } Context viewContext; if (parent != null && inheritContext) { viewContext = parent.getContext(); } else { viewContext = mContext; } // Apply a theme wrapper, if requested. final TypedArray ta = viewContext.obtainStyledAttributes(attrs, ATTRS_THEME); final int themeResId = ta.getResourceId(0, 0); if (themeResId != 0) { viewContext = new ContextThemeWrapper(viewContext, themeResId); } ta.recycle(); if (name.equals(TAG_1995)) { // Let's party like it's 1995! return new BlinkLayout(viewContext, attrs); } if (DEBUG) System.out.println("******** Creating view: " + name); try { View view; if (mFactory2 != null) { view = mFactory2.onCreateView(parent, name, viewContext, attrs); } else if (mFactory != null) { view = mFactory.onCreateView(name, viewContext, attrs); } else { view = null; } if (view == null && mPrivateFactory != null) { view = mPrivateFactory.onCreateView(parent, name, viewContext, attrs); } if (view == null) { final Object lastContext = mConstructorArgs[0]; mConstructorArgs[0] = viewContext; try { if (-1 == name.indexOf('.')) { view = onCreateView(parent, name, attrs); } else { view = createView(name, null, attrs); } } finally { mConstructorArgs[0] = lastContext; } } if (DEBUG) System.out.println("Created view is: " + view); return view; } catch (InflateException e) { throw e; } catch (ClassNotFoundException e) { InflateException ie = new InflateException(attrs.getPositionDescription() + ": Error inflating class " + name); ie.initCause(e); throw ie; } catch (Exception e) { InflateException ie = new InflateException(attrs.getPositionDescription() + ": Error inflating class " + name); ie.initCause(e); throw ie; } } ~~~ 上面這個方法中，如果傳過來的名字沒有“.”，會認為是一個內置view。會調用onCreateView來解析這個View。PhoneLayoutInflater的onCreateView就是為內置的View加上前綴，如android.widget等。然后再調用createView()來進行view的構造。 ~~~ 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); //constructor是從緩存中取出的構造函數 if (constructor == null) { // Class not found in the cache, see if it's real, and try to add it //如果prefix不為空就構造view路徑并加載 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); } } 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 //通過反射構造view 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); 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; } 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); } } ~~~ 又是一大堆代碼，但它其實就是使用view的完整路徑將類加載到虛擬機中，通過構造函數來創建view對象，這個過程是通過反射。最后返回view。這個就解析了單個view。那如果是一棵樹，則交給rInflate來處理。看下代碼： ~~~ void rInflate(XmlPullParser parser, View parent, final AttributeSet attrs, boolean finishInflate, boolean inheritContext) 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)) { parseRequestFocus(parser, parent); } else if (TAG_TAG.equals(name)) { parseViewTag(parser, parent, attrs); } else if (TAG_INCLUDE.equals(name)) { if (parser.getDepth() == 0) { throw new InflateException("<include /> cannot be the root element"); } parseInclude(parser, parent, attrs, inheritContext); } else if (TAG_MERGE.equals(name)) { throw new InflateException("<merge /> must be the root element"); } else { final View view = createViewFromTag(parent, name, attrs, inheritContext); final ViewGroup viewGroup = (ViewGroup) parent; final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs); rInflate(parser, view, attrs, true, true); viewGroup.addView(view, params); } } if (finishInflate) parent.onFinishInflate(); } /** * Parses a <code>&lt;request-focus&gt;</code> element and requests focus on * the containing View. */ private void parseRequestFocus(XmlPullParser parser, View view) throws XmlPullParserException, IOException { int type; view.requestFocus(); final int currentDepth = parser.getDepth(); while (((type = parser.next()) != XmlPullParser.END_TAG || parser.getDepth() > currentDepth) && type != XmlPullParser.END_DOCUMENT) { // Empty } } ~~~ 普希金通過深度優先遍歷來構造視圖樹。每解析一個view就會遞歸調用rInflate。view的結構一層包一層，其實就是標準的組合設計模式實現的。整個視圖構建完后就會在onResume之后，內容就會出現在界面中。? 到此，LayoutInflater加載View的過程就分析完了。還是比較簡單易懂的。 ### 布局加載優化 通過上面的分析，我們可以提出幾點常用的布局優化手段：? 1.盡量使用相對布局，減少不必要層級結構。? 2.使用merge屬性。使用它可以有效的將某些符合條件的多余的層級優化掉，使用merge標簽還是有一些限制的，具體是：merge只能用在布局XML文件的根元素；使用merge來inflate一個布局時，必須指定一個ViewGroup作為其父元素，并且要設置inflate的attachToRoot參數為true。；不能在ViewStub中使用merge標簽。? 3.使用ViewStub。一個輕量級的頁面，我們通常使用它來做預加載處理，來改善頁面加載速度和提高流暢性，ViewStub本身不會占用層級，它最終會被它指定的層級取代。ViewStub也是有一些缺點，譬如：ViewStub只能Inflate一次，之后ViewStub對象會被置為空。VIewStub中不能嵌套merge標簽。? 4.使用include。這個標簽是為了布局重用。? 當然還有很多優化手段和工具可以使用，在此不一一羅列。關于布局還是有很大的學問要去深入研究的。