Android中将xml布局文件转化为View树的过程分析（上）
有好几周没写东西了，一方面是因为前几个周末都有些事情，另外也是因为没能找到好的写作方向，或者说有些话题
值得分享、写作，可是自己积累还不够，没办法只好闷头继续研究了。这段时间一边在写代码，一边也在想Android中
究竟是如何将R.layout.xxx_view.xml这样的布局文件加载到Android系统的view层次结构中的（即我们常说的view树）。
这期间一方面自己研究了下源码，另一方面也在网上搜索了下相关文章，发现了2篇很不错的同主题文章，推荐给大家：
http://blog.csdn.net/qinjuning/article/details/7226787 & http://blog.csdn.net/bigconvience/article/details/28626631。
我们在开发中接触最早的应该算是Activity.setContentView(int resourceId)方法了，我们知道在Activity的onCreate中调用此
方法可以把我们提供的根布局文件加载到activity中并显示出来。很自然地我们就从它开始说起吧，废话不多说上代码：
/** * Set the activity content from a layout resource. The resource will be * inflated, adding all top-level views to the activity. * * @param layoutResID Resource ID to be inflated. * * @see #setContentView(android.view.View) * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams) */ public void setContentView(int layoutResID) { // 实际上其内部都是delegate给了getWindow()方法 getWindow().setContentView(layoutResID); initActionBar(); } /** * Set the activity content to an explicit view. This view is placed * directly into the activity's view hierarchy. It can itself be a complex * view hierarchy. When calling this method, the layout parameters of the * specified view are ignored. Both the width and the height of the view are * set by default to {@link ViewGroup.LayoutParams#MATCH_PARENT}. To use * your own layout parameters, invoke * {@link #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)} * instead. * * @param view The desired content to display. * * @see #setContentView(int) * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams) */ public void setContentView(View view) { getWindow().setContentView(view); initActionBar(); } /** * Set the activity content to an explicit view. This view is placed * directly into the activity's view hierarchy. It can itself be a complex * view hierarchy. * * @param view The desired content to display. * @param params Layout parameters for the view. * * @see #setContentView(android.view.View) * @see #setContentView(int) */ public void setContentView(View view, ViewGroup.LayoutParams params) { getWindow().setContentView(view, params); initActionBar(); } /** * Add an additional content view to the activity. Added after any existing * ones in the activity -- existing views are NOT removed. * * @param view The desired content to display. * @param params Layout parameters for the view. */ public void addContentView(View view, ViewGroup.LayoutParams params) { getWindow().addContentView(view, params); initActionBar(); }
我们可以看到setContentView方法内部都delegate给了getWindow()方法，这里顺便也把addContentView提及了下，setXXX有
替换的意思，addXXX则是往后面在加一个，即以前的还在。紧接着我们看下Activity里的window是咋来的吧，代码如下：
private Window mWindow; // Activity的一个字段
/** * Retrieve the current {@link android.view.Window} for the activity. * This can be used to directly access parts of the Window API that * are not available through Activity/Screen. * * @return Window The current window, or null if the activity is not * visual. */ public Window getWindow() { return mWindow; } final void attach(Context context, ActivityThread aThread, Instrumentation instr, IBinder token, Application application, Intent intent, ActivityInfo info, CharSequence title, Activity parent, String id, NonConfigurationInstances lastNonConfigurationInstances, Configuration config) { attach(context, aThread, instr, token, 0, application, intent, info, title, parent, id, lastNonConfigurationInstances, config); } final void attach(Context context, ActivityThread aThread, Instrumentation instr, IBinder token, int ident, Application application, Intent intent, ActivityInfo info, CharSequence title, Activity parent, String id, NonConfigurationInstances lastNonConfigurationInstances, Configuration config) { attachBaseContext(context); mFragments.attachActivity(this, mContainer, null); mWindow = PolicyManager.makeNewWindow(this); // 注意这行代码，这里实际上创建了一个PhoneWindow的实例 mWindow.setCallback(this); // window对象里的Callback接口的实现是Activity mWindow.getLayoutInflater().setPrivateFactory(this); if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) { mWindow.setSoftInputMode(info.softInputMode); } if (info.uiOptions != 0) { mWindow.setUiOptions(info.uiOptions); } mUiThread = Thread.currentThread(); mMainThread = aThread; mInstrumentation = instr; mToken = token; mIdent = ident; mApplication = application; mIntent = intent; mComponent = intent.getComponent(); mActivityInfo = info; mTitle = title; mParent = parent; mEmbeddedID = id; mLastNonConfigurationInstances = lastNonConfigurationInstances; mWindow.setWindowManager( (WindowManager)context.getSystemService(Context.WINDOW_SERVICE), mToken, mComponent.flattenToString(), (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0); if (mParent != null) { mWindow.setContainer(mParent.getWindow()); } mWindowManager = mWindow.getWindowManager(); mCurrentConfig = config; }
从代码我们可以看出是在Activity.attach方法中对mWindow进行初始化的，这里也顺便解释下Window、Activity、View的区别和联系：
Window是个封装了窗体样式和行为的策略抽象类，它的实例作为顶层view被加到window manager里面；它提供了标准的UI策略，
如背景、标题栏、默认的key处理逻辑等等。在Android系统中有一个唯一的实现PhoneWindow，当我们需要window的
时候就会有一个PhoneWindow的实例被new出来。每个Activity都有一个与之关联的window对象，Activity在其上绘制UI。
Window对象里又有一个mDecor对象，它是window里的顶层view（也就是说view树的层次结构从它开始，它是view树的根）。
更多的解释可以参考这个问题： http://stackoverflow.com/questions/9451755/what-is-an-android-window 。
接着我们看看上面代码里具体给mWindow对象赋值的代码，先来看看com.android.internal.policy.PolicyManager类：
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); // 加载class文件 sPolicy = (IPolicy)policyClass.newInstance(); // 根据Class对象，创建个实例 } 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); } } // Cannot instantiate this class private PolicyManager() {} // The static methods to spawn new policy-specific objects public static Window makeNewWindow(Context context) { return sPolicy.makeNewWindow(context); } public static LayoutInflater makeNewLayoutInflater(Context context) { return sPolicy.makeNewLayoutInflater(context); } public static WindowManagerPolicy makeNewWindowManager() { return sPolicy.makeNewWindowManager(); } public static FallbackEventHandler makeNewFallbackEventHandler(Context context) { return sPolicy.makeNewFallbackEventHandler(context); } }
接着我们看下sPolicy的具体实现类，com.android.internal.policy.impl.Policy.java文件：
public class Policy implements IPolicy { private static final String TAG = "PhonePolicy"; private static final String[] preload_classes = { "com.android.internal.policy.impl.PhoneLayoutInflater", "com.android.internal.policy.impl.PhoneWindow", "com.android.internal.policy.impl.PhoneWindow$1", "com.android.internal.policy.impl.PhoneWindow$DialogMenuCallback", "com.android.internal.policy.impl.PhoneWindow$DecorView", "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState", "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState$SavedState", }; static { // For performance reasons, preload some policy specific classes when // the policy gets loaded. for (String s : preload_classes) { try { Class.forName(s); // 预加载这些类的class文件，以便后面new他们的对象 } catch (ClassNotFoundException ex) { Log.e(TAG, "Could not preload class for phone policy: " + s); } } } public Window makeNewWindow(Context context) { return new PhoneWindow(context); // 至此我们看到了Android系统里真正且唯一的Window类型，PhoneWindow } public LayoutInflater makeNewLayoutInflater(Context context) { return new PhoneLayoutInflater(context); // LayoutInflater接口的实际实现者，以后我们的代码里出现的类似 } // (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE) // 这样的代码，返回的都是此对象。 public WindowManagerPolicy makeNewWindowManager() { return new PhoneWindowManager(); } public FallbackEventHandler makeNewFallbackEventHandler(Context context) { return new PhoneFallbackEventHandler(context); } }
至此我们看清楚了Activity中的mWindow对象实际上是PhoneWindow的实例。搞清楚了window对象咋来的，接下来我们可以
分析其setContentView方法了，代码如下：
// This is the top-level view of the window, containing the window decor. private DecorView mDecor; // window中的顶层view // This is the view in which the window contents are placed. It is either // mDecor itself, or a child of mDecor where the contents go. private ViewGroup mContentParent; // Android为我们提供的window布局文件中id=@android:id/content的view // 后面我们会看几个典型的window布局文件 private LayoutInflater mLayoutInflater; public PhoneWindow(Context context) { super(context); mLayoutInflater = LayoutInflater.from(context); // 我们在上文中提到的通过context.getSystemService实现 } @Override public void setContentView(int layoutResID) { if (mContentParent == null) { // 第一次调用的时候执行 installDecor(); } else { // 可以看出setContentView支持多次调用，只是相当于把之前的view层次结构扔掉，从头再来而已 mContentParent.removeAllViews(); } mLayoutInflater.inflate(layoutResID, mContentParent); // 将我们dev提供的顶层layout文件加到mContentParent里面 final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); // 调用回调函数，一般是Activity或Dialog } } @Override public void setContentView(View view) { // 默认的LayoutParams是MATCH_PARENT，当然你也可以指定 setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); } @Override public void setContentView(View view, ViewGroup.LayoutParams params) { if (mContentParent == null) { installDecor(); } else { mContentParent.removeAllViews(); } mContentParent.addView(view, params); final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); } } @Override public void addContentView(View view, ViewGroup.LayoutParams params) { if (mContentParent == null) { installDecor(); } // 注意相比setContentView来说，少了mContentParent.removeAllViews()调用，
// 所以效果就是之前的view层次结构还在，只是新增了一个view mContentParent.addView(view, params); final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); } }
接着我们看看installDecor相关的实现：
private void installDecor() { if (mDecor == null) { mDecor = generateDecor(); // new一个DecorView（一种特殊的FrameLayout） mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS); mDecor.setIsRootNamespace(true); if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) { mDecor.postOnAnimation(mInvalidatePanelMenuRunnable); } } if (mContentParent == null) { mContentParent = generateLayout(mDecor); // 初始化mContentParent // Set up decor part of UI to ignore fitsSystemWindows if appropriate. mDecor.makeOptionalFitsSystemWindows(); mTitleView = (TextView)findViewById(com.android.internal.R.id.title); if (mTitleView != null) { mTitleView.setLayoutDirection(mDecor.getLayoutDirection()); if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) { View titleContainer = findViewById(com.android.internal.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); } } else { mActionBar = (ActionBarView) findViewById(com.android.internal.R.id.action_bar); if (mActionBar != null) { mActionBar.setWindowCallback(getCallback()); if (mActionBar.getTitle() == null) { mActionBar.setWindowTitle(mTitle); } final int localFeatures = getLocalFeatures(); if ((localFeatures & (1 << FEATURE_PROGRESS)) != 0) { mActionBar.initProgress(); } if ((localFeatures & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) { mActionBar.initIndeterminateProgress(); } final ActionBarOverlayLayout abol = (ActionBarOverlayLayout) findViewById( com.android.internal.R.id.action_bar_overlay_layout); if (abol != null) { abol.setOverlayMode( (localFeatures & (1 << FEATURE_ACTION_BAR_OVERLAY)) != 0); } boolean splitActionBar = false; final boolean splitWhenNarrow = (mUiOptions & ActivityInfo.UIOPTION_SPLIT_ACTION_BAR_WHEN_NARROW) != 0; if (splitWhenNarrow) { splitActionBar = getContext().getResources().getBoolean( com.android.internal.R.bool.split_action_bar_is_narrow); } else { splitActionBar = getWindowStyle().getBoolean( com.android.internal.R.styleable.Window_windowSplitActionBar, false); } final ActionBarContainer splitView = (ActionBarContainer) findViewById( com.android.internal.R.id.split_action_bar); if (splitView != null) { mActionBar.setSplitView(splitView); mActionBar.setSplitActionBar(splitActionBar); mActionBar.setSplitWhenNarrow(splitWhenNarrow); final ActionBarContextView cab = (ActionBarContextView) findViewById( com.android.internal.R.id.action_context_bar); cab.setSplitView(splitView); cab.setSplitActionBar(splitActionBar); cab.setSplitWhenNarrow(splitWhenNarrow); } else if (splitActionBar) { Log.e(TAG, "Requested split action bar with " + "incompatible window decor! Ignoring request."); } if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) != 0 || (mIconRes != 0 && !mActionBar.hasIcon())) { mActionBar.setIcon(mIconRes); } else if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) == 0 && mIconRes == 0 && !mActionBar.hasIcon()) { mActionBar.setIcon( getContext().getPackageManager().getDefaultActivityIcon()); mResourcesSetFlags |= FLAG_RESOURCE_SET_ICON_FALLBACK; } if ((mResourcesSetFlags & FLAG_RESOURCE_SET_LOGO) != 0 || (mLogoRes != 0 && !mActionBar.hasLogo())) { mActionBar.setLogo(mLogoRes); } // Post the panel invalidate for later; avoid application onCreateOptionsMenu // being called in the middle of onCreate or similar. mDecor.post(new Runnable() { public void run() { // Invalidate if the panel menu hasn't been created before this. PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false); if (!isDestroyed() && (st == null || st.menu == null)) { invalidatePanelMenu(FEATURE_ACTION_BAR); } } }); } } } } protected DecorView generateDecor() { // 我会在合适的时候专门分析下DecorView return new DecorView(getContext(), -1); } protected ViewGroup generateLayout(DecorView decor) { // Apply data from current theme. TypedArray a = getWindowStyle(); if (false) { System.out.println("From style:"); String s = "Attrs:"; for (int i = 0; i < com.android.internal.R.styleable.Window.length; i++) { s = s + " " + Integer.toHexString(com.android.internal.R.styleable.Window[i]) + "=" + a.getString(i); } System.out.println(s); } // 接下来的一大堆代码都是从window的theme中获取属性值，然后调用相应的requestFeature或setFlags方法 mIsFloating = a.getBoolean(com.android.internal.R.styleable.Window_windowIsFloating, false); int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR) & (~getForcedWindowFlags()); if (mIsFloating) { // 比如这里，如果是floating的（如dialog），则设置layout为WRAP_CONTENT，即非全屏 setLayout(WRAP_CONTENT, WRAP_CONTENT); setFlags(0, flagsToUpdate); } else { setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowNoTitle, false)) { requestFeature(FEATURE_NO_TITLE); } else if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionBar, false)) { // Don't allow an action bar if there is no title. requestFeature(FEATURE_ACTION_BAR); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionBarOverlay, false)) { requestFeature(FEATURE_ACTION_BAR_OVERLAY); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionModeOverlay, false)) { requestFeature(FEATURE_ACTION_MODE_OVERLAY); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowFullscreen, false)) { setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags())); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowTranslucentStatus, false)) { setFlags(FLAG_TRANSLUCENT_STATUS, FLAG_TRANSLUCENT_STATUS & (~getForcedWindowFlags())); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowTranslucentNavigation, false)) { setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION & (~getForcedWindowFlags())); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowOverscan, false)) { setFlags(FLAG_LAYOUT_IN_OVERSCAN, FLAG_LAYOUT_IN_OVERSCAN&(~getForcedWindowFlags())); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowShowWallpaper, false)) { setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags())); } if (a.getBoolean(com.android.internal.R.styleable.Window_windowEnableSplitTouch, getContext().getApplicationInfo().targetSdkVersion >= android.os.Build.VERSION_CODES.HONEYCOMB)) { setFlags(FLAG_SPLIT_TOUCH, FLAG_SPLIT_TOUCH&(~getForcedWindowFlags())); } a.getValue(com.android.internal.R.styleable.Window_windowMinWidthMajor, mMinWidthMajor); a.getValue(com.android.internal.R.styleable.Window_windowMinWidthMinor, mMinWidthMinor); if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedWidthMajor)) { if (mFixedWidthMajor == null) mFixedWidthMajor = new TypedValue(); a.getValue(com.android.internal.R.styleable.Window_windowFixedWidthMajor, mFixedWidthMajor); } if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedWidthMinor)) { if (mFixedWidthMinor == null) mFixedWidthMinor = new TypedValue(); a.getValue(com.android.internal.R.styleable.Window_windowFixedWidthMinor, mFixedWidthMinor); } if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedHeightMajor)) { if (mFixedHeightMajor == null) mFixedHeightMajor = new TypedValue(); a.getValue(com.android.internal.R.styleable.Window_windowFixedHeightMajor, mFixedHeightMajor); } if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedHeightMinor)) { if (mFixedHeightMinor == null) mFixedHeightMinor = new TypedValue(); a.getValue(com.android.internal.R.styleable.Window_windowFixedHeightMinor, mFixedHeightMinor); } final Context context = getContext(); final int targetSdk = context.getApplicationInfo().targetSdkVersion; final boolean targetPreHoneycomb = targetSdk < android.os.Build.VERSION_CODES.HONEYCOMB; final boolean targetPreIcs = targetSdk < android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH; final boolean targetHcNeedsOptions = context.getResources().getBoolean( com.android.internal.R.bool.target_honeycomb_needs_options_menu); final boolean noActionBar = !hasFeature(FEATURE_ACTION_BAR) || hasFeature(FEATURE_NO_TITLE); if (targetPreHoneycomb || (targetPreIcs && targetHcNeedsOptions && noActionBar)) { addFlags(WindowManager.LayoutParams.FLAG_NEEDS_MENU_KEY); } else { clearFlags(WindowManager.LayoutParams.FLAG_NEEDS_MENU_KEY); } if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion >= android.os.Build.VERSION_CODES.HONEYCOMB) { if (a.getBoolean( com.android.internal.R.styleable.Window_windowCloseOnTouchOutside, false)) { setCloseOnTouchOutsideIfNotSet(true); } } WindowManager.LayoutParams params = getAttributes(); if (!hasSoftInputMode()) { params.softInputMode = a.getInt( com.android.internal.R.styleable.Window_windowSoftInputMode, params.softInputMode); } if (a.getBoolean(com.android.internal.R.styleable.Window_backgroundDimEnabled, mIsFloating)) { /* All dialogs should have the window dimmed */ if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == 0) { params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND; } if (!haveDimAmount()) { params.dimAmount = a.getFloat( android.R.styleable.Window_backgroundDimAmount, 0.5f); } } if (params.windowAnimations == 0) { params.windowAnimations = a.getResourceId( com.android.internal.R.styleable.Window_windowAnimationStyle, 0); } // The rest are only done if this window is not embedded; otherwise, // the values are inherited from our container. if (getContainer() == null) { if (mBackgroundDrawable == null) { if (mBackgroundResource == 0) { mBackgroundResource = a.getResourceId( com.android.internal.R.styleable.Window_windowBackground, 0); } if (mFrameResource == 0) { mFrameResource = a.getResourceId(com.android.internal.R.styleable.Window_windowFrame, 0); } if (false) { System.out.println("Background: " + Integer.toHexString(mBackgroundResource) + " Frame: " + Integer.toHexString(mFrameResource)); } } mTextColor = a.getColor(com.android.internal.R.styleable.Window_textColor, 0xFF000000); } // Inflate the window decor. // 接下来就是根据设定好的features（即窗口风格属性）选择对应的xml文件 int layoutResource; int features = getLocalFeatures(); // System.out.println("Features: 0x" + Integer.toHexString(features)); if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) { if (mIsFloating) { TypedValue res = new TypedValue(); getContext().getTheme().resolveAttribute( com.android.internal.R.attr.dialogTitleIconsDecorLayout, res, true); layoutResource = res.resourceId; } else { layoutResource = com.android.internal.R.layout.screen_title_icons; } // XXX Remove this once action bar supports these features. removeFeature(FEATURE_ACTION_BAR); // System.out.println("Title Icons!"); } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0 && (features & (1 << FEATURE_ACTION_BAR)) == 0) { // Special case for a window with only a progress bar (and title). // XXX Need to have a no-title version of embedded windows. layoutResource = com.android.internal.R.layout.screen_progress; // System.out.println("Progress!"); } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) { // Special case for a window with a custom title. // If the window is floating, we need a dialog layout if (mIsFloating) { TypedValue res = new TypedValue(); getContext().getTheme().resolveAttribute( com.android.internal.R.attr.dialogCustomTitleDecorLayout, res, true); layoutResource = res.resourceId; } else { layoutResource = com.android.internal.R.layout.screen_custom_title; } // XXX Remove this once action bar supports these features. removeFeature(FEATURE_ACTION_BAR); } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) { // If no other features and not embedded, only need a title. // If the window is floating, we need a dialog layout if (mIsFloating) { TypedValue res = new TypedValue(); getContext().getTheme().resolveAttribute( com.android.internal.R.attr.dialogTitleDecorLayout, res, true); layoutResource = res.resourceId; } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) { layoutResource = com.android.internal.R.layout.screen_action_bar; } else { layoutResource = com.android.internal.R.layout.screen_title; } // System.out.println("Title!"); } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) { layoutResource = com.android.internal.R.layout.screen_simple_overlay_action_mode; } else { // Embedded, so no decoration is needed. layoutResource = com.android.internal.R.layout.screen_simple; // System.out.println("Simple!"); } mDecor.startChanging(); // 回调点，表示开始。。。 View in = mLayoutInflater.inflate(layoutResource, null); // 将选定的layout文件inflate成view decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); // 将其添加到decor中 ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT); // 找到系统layout文件中为我们客户端布局预留 if (contentParent == null) { // 的placeholder，我们的Activity布局将从这里开始。 throw new RuntimeException("Window couldn't find content container view"); } if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) { ProgressBar progress = getCircularProgressBar(false); if (progress != null) { progress.setIndeterminate(true); } } // Remaining setup -- of background and title -- that only applies // to top-level windows. if (getContainer() == null) { Drawable drawable = mBackgroundDrawable; if (mBackgroundResource != 0) { drawable = getContext().getResources().getDrawable(mBackgroundResource); } mDecor.setWindowBackground(drawable); drawable = null; if (mFrameResource != 0) { drawable = getContext().getResources().getDrawable(mFrameResource); } mDecor.setWindowFrame(drawable); // System.out.println("Text=" + Integer.toHexString(mTextColor) + // " Sel=" + Integer.toHexString(mTextSelectedColor) + // " Title=" + Integer.toHexString(mTitleColor)); if (mTitleColor == 0) { mTitleColor = mTextColor; } if (mTitle != null) { setTitle(mTitle); } setTitleColor(mTitleColor); } mDecor.finishChanging(); // 回调点，表示结束了。。。 return contentParent; // 返回客户端（Activity）布局的parent view }
mContentParent被正确初始化后，在setContentView中通过mLayoutInflater.inflate(layoutResID, mContentParent);
这样的代码就可以将Activity的布局文件加到整个view层次结构中，这样我们的layout xml就和系统的联系起来了。
下面我们看几个前面说到的系统提供的布局文件，针对某个特定的feature属性，代码如下：
<!-- screen_title.xml --> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:fitsSystemWindows="true"> <!-- Popout bar for action modes --> <ViewStub android:id="@+id/action_mode_bar_stub" android:inflatedId="@+id/action_mode_bar" android:layout="@layout/action_mode_bar" android:layout_width="match_parent" android:layout_height="wrap_content" /> <FrameLayout android:layout_width="match_parent" android:layout_height="?android:attr/windowTitleSize" style="?android:attr/windowTitleBackgroundStyle"> <TextView android:id="@android:id/title" style="?android:attr/windowTitleStyle" android:background="@null" android:fadingEdge="horizontal" android:gravity="center_vertical" android:layout_width="match_parent" android:layout_height="match_parent" /> </FrameLayout> <FrameLayout android:id="@android:id/content" // 注意这里的共同点，这就是给客户端程序预留的placeholder，mContentParent view android:layout_width="match_parent" android:layout_height="0dip" android:layout_weight="1" android:foregroundGravity="fill_horizontal|top" android:foreground="?android:attr/windowContentOverlay" /> </LinearLayout> <!-- screen_simple.xml --> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:fitsSystemWindows="true" android:orientation="vertical"> <ViewStub android:id="@+id/action_mode_bar_stub" android:inflatedId="@+id/action_mode_bar" android:layout="@layout/action_mode_bar" android:layout_width="match_parent" android:layout_height="wrap_content" /> <FrameLayout android:id="@android:id/content" // 共同点，id都是android:id/content android:layout_width="match_parent" android:layout_height="match_parent" android:foregroundInsidePadding="false" android:foregroundGravity="fill_horizontal|top" android:foreground="?android:attr/windowContentOverlay" /> </LinearLayout>
在我们的开发中，还经常会使用LayoutInflater.inflate方法来将某一个xml文件动态添加到view层次结构中，这种方式简直太棒了。
当然为了避免篇幅过长，我会在下一篇文章中专门分析下这种情况，敬请期待。终于可以收工了，准备看西班牙-荷兰的比赛了，哈哈。。。
