Android之View绘制流程开胃菜---setContentView(...)详细分析

时间 2019-11-26

标签 android view 绘制流程开胃菜 setcontentview 详细分析栏目 Android 繁體版

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1 为何要分析setContentView方法android

做为安卓开发者相信大部分都有意或者无心看过以下图示：PhoneWindow,DecorView这些究竟都是些神马玩意？图示的层级关系是怎么来的？咱们本身所写的布局是怎么加载到窗体上的？以及在上一篇《Android事件传递机制详解及最新源码分析——Activity篇》中提到过咱们在调用setContentView设置布局的时候其实都是被放置在id为content的FrameLayout 布局中的，这里又是什么鬼？带着这些问题咱们一块儿探讨下setContentView方法究竟作了些什么。windows

2 分析setContentView方法（API23）app

咱们平时调用setContentView，例如：setContentView(R.layout.xxx);点进源码都是先调用Activity中的setContentView方法，咱们就从Activity中的setContentView方法开始分析。ide

Activity的源码中有三个重载的setContentView方法，以下：源码分析

 1 public void setContentView(@LayoutRes int layoutResID) {  2  getWindow().setContentView(layoutResID);  3  initWindowDecorActionBar();  4  }  5 
 6 public void setContentView(View view) {  7  getWindow().setContentView(view);  8  initWindowDecorActionBar();  9  } 10 
11 public void setContentView(View view, ViewGroup.LayoutParams params) { 12  getWindow().setContentView(view, params); 13  initWindowDecorActionBar(); 14     }

能够看到三个方法都是又调用了getWindow().setContentView(...);在上一篇文章中分析过getWindow()返回mWindow对象，mWindow定义是Windo类型，实际初始化的时候初始化为PhoneWindow，源码以下：布局

private Window mWindow; mWindow = new PhoneWindow(this);

这里说明一下：Window 是抽象类，主要提供一些绘制窗口的一些公用方法，PhoneWindow是Window的具体继承实现类。post

咱们看看Window类中setContentView方法，源码以下：优化

public abstract void setContentView(@LayoutRes int layoutResID); public abstract void setContentView(View view); public abstract void setContentView(View view, ViewGroup.LayoutParams params);

看到了吧，这里只是三个抽象方法而已，具体逻辑须要子类本身去实现。ui

接下来，咱们就就去PhoneWindow中找一下吧，源码以下：

 @Override 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); } mContentParent.requestApplyInsets(); final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); } } @Override public void setContentView(View view) { setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); } @Override public void setContentView(View view, ViewGroup.LayoutParams params) { // 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)) { view.setLayoutParams(params); final Scene newScene = new Scene(mContentParent, view); transitionTo(newScene); } else { mContentParent.addView(view, params); } mContentParent.requestApplyInsets(); final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); } }

看到了吧，在子类PhoneWindow中有具体实现，而且setContentView(View view)实际上也是调用的setContentView(View view, ViewGroup.LayoutParams params)，只不过params参数默认传入为MATCH_PARENT。而且setContentView(int layoutResID)与setContentView(View view, ViewGroup.LayoutParams params)方法代码逻辑是同样的，这里咱们选取setContentView(int layoutResID)方法加以分析便可。

到这里咱们明白平时调用的setContentView(R.layout.xxx)方法实际上调用的是PhoneWindow中的setContentView(int layoutResID)方法，接下来咱们着重分析此方法。

3 分析PhoneWindow中的setContentView(int layoutResID)方法（API23）

源码以下：

 1  @Override  2     public void setContentView(int layoutResID) {  3         // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window  4         // decor, when theme attributes and the like are crystalized. Do not check the feature  5         // before this happens.
 6         if (mContentParent == null) {  7  installDecor();  8         } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {  9  mContentParent.removeAllViews(); 10  } 11 
12         if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) { 13             final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID, 14  getContext()); 15  transitionTo(newScene); 16         } else { 17  mLayoutInflater.inflate(layoutResID, mContentParent); 18  } 19  mContentParent.requestApplyInsets(); 20         final Callback cb = getCallback(); 21         if (cb != null && !isDestroyed()) { 22  cb.onContentChanged(); 23  } 24     }

第6行代码判断mContentParent 是否为空，mContentParent 是PhoneWindow中定义的一个ViewGroup类型实例。第一次运行的时候mContentParent 为null，则进入判断执行第7行代码

installDecor()，咱们看看installDecor()方法都作了什么源码以下：这里只列出主要代码

 1 private void installDecor() {  2         if (mDecor == null) {  3             mDecor = generateDecor();  4  ...  5  }  6         if (mContentParent == null) {  7             mContentParent = generateLayout(mDecor);  8  ...  9  } 10  .... 11 }

第2行代码判断mDecor是否为null，为null则执行generateDecor()代码并对mDecor赋值，mDecor是DecorView的一个实例，DecorView是PhoneWindow的内部类，定义以下：

private final class DecorView extends FrameLayout implements RootViewSurfaceTaker

看到了吧，DecorView其实就是FrameLayout 的子类，对FrameLayout 进行装饰，加强其某些功能。

咱们继续看generateDecor()源码：

1    protected DecorView generateDecor() { 2         return new DecorView(getContext(), -1); 3     }

很简单吧就是生成DecorView对象而且返回，这里没什么要多说的。

返回installDecor()方法咱们继续向下分析。

第6行代码又是判断mContentParent 是否为null,是则执行generateLayout(mDecor)方法并将返回值赋值给mContentParent 。

那咱们就继续看generateLayout(mDecor)源码：

 1 protected ViewGroup generateLayout(DecorView decor) {  2         // Apply data from current theme.
 3 
 4         TypedArray a = getWindowStyle();  5 
 6         if (false) {  7             System.out.println("From style:");  8             String s = "Attrs:";  9             for (int i = 0; i < R.styleable.Window.length; i++) {  10                 s = s + " " + Integer.toHexString(R.styleable.Window[i]) + "="
 11                         + a.getString(i);  12  }  13  System.out.println(s);  14  }  15 
 16         mIsFloating = a.getBoolean(R.styleable.Window_windowIsFloating, false);  17         int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)  18                 & (~getForcedWindowFlags());  19         if (mIsFloating) {  20  setLayout(WRAP_CONTENT, WRAP_CONTENT);  21             setFlags(0, flagsToUpdate);  22         } else {  23             setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);  24  }  25 
 26         if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {  27  requestFeature(FEATURE_NO_TITLE);  28         } else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {  29             // Don't allow an action bar if there is no title.
 30  requestFeature(FEATURE_ACTION_BAR);  31  }  32 
 33         if (a.getBoolean(R.styleable.Window_windowActionBarOverlay, false)) {  34  requestFeature(FEATURE_ACTION_BAR_OVERLAY);  35  }  36 
 37         if (a.getBoolean(R.styleable.Window_windowActionModeOverlay, false)) {  38  requestFeature(FEATURE_ACTION_MODE_OVERLAY);  39  }  40 
 41         if (a.getBoolean(R.styleable.Window_windowSwipeToDismiss, false)) {  42  requestFeature(FEATURE_SWIPE_TO_DISMISS);  43  }  44 
 45         if (a.getBoolean(R.styleable.Window_windowFullscreen, false)) {  46             setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));  47  }  48 
 49         if (a.getBoolean(R.styleable.Window_windowTranslucentStatus,  50                 false)) {  51  setFlags(FLAG_TRANSLUCENT_STATUS, FLAG_TRANSLUCENT_STATUS  52                     & (~getForcedWindowFlags()));  53  }  54 
 55         if (a.getBoolean(R.styleable.Window_windowTranslucentNavigation,  56                 false)) {  57  setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION  58                     & (~getForcedWindowFlags()));  59  }  60 
 61         if (a.getBoolean(R.styleable.Window_windowOverscan, false)) {  62             setFlags(FLAG_LAYOUT_IN_OVERSCAN, FLAG_LAYOUT_IN_OVERSCAN&(~getForcedWindowFlags()));  63  }  64 
 65         if (a.getBoolean(R.styleable.Window_windowShowWallpaper, false)) {  66             setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags()));  67  }  68 
 69         if (a.getBoolean(R.styleable.Window_windowEnableSplitTouch,  70  getContext().getApplicationInfo().targetSdkVersion  71                         >= android.os.Build.VERSION_CODES.HONEYCOMB)) {  72             setFlags(FLAG_SPLIT_TOUCH, FLAG_SPLIT_TOUCH&(~getForcedWindowFlags()));  73  }  74 
 75  a.getValue(R.styleable.Window_windowMinWidthMajor, mMinWidthMajor);  76  a.getValue(R.styleable.Window_windowMinWidthMinor, mMinWidthMinor);  77         if (a.hasValue(R.styleable.Window_windowFixedWidthMajor)) {  78             if (mFixedWidthMajor == null) mFixedWidthMajor = new TypedValue();  79  a.getValue(R.styleable.Window_windowFixedWidthMajor,  80  mFixedWidthMajor);  81  }  82         if (a.hasValue(R.styleable.Window_windowFixedWidthMinor)) {  83             if (mFixedWidthMinor == null) mFixedWidthMinor = new TypedValue();  84  a.getValue(R.styleable.Window_windowFixedWidthMinor,  85  mFixedWidthMinor);  86  }  87         if (a.hasValue(R.styleable.Window_windowFixedHeightMajor)) {  88             if (mFixedHeightMajor == null) mFixedHeightMajor = new TypedValue();  89  a.getValue(R.styleable.Window_windowFixedHeightMajor,  90  mFixedHeightMajor);  91  }  92         if (a.hasValue(R.styleable.Window_windowFixedHeightMinor)) {  93             if (mFixedHeightMinor == null) mFixedHeightMinor = new TypedValue();  94  a.getValue(R.styleable.Window_windowFixedHeightMinor,  95  mFixedHeightMinor);  96  }  97         if (a.getBoolean(R.styleable.Window_windowContentTransitions, false)) {  98  requestFeature(FEATURE_CONTENT_TRANSITIONS);  99  } 100         if (a.getBoolean(R.styleable.Window_windowActivityTransitions, false)) { 101  requestFeature(FEATURE_ACTIVITY_TRANSITIONS); 102  } 103 
104         final Context context = getContext(); 105         final int targetSdk = context.getApplicationInfo().targetSdkVersion; 106         final boolean targetPreHoneycomb = targetSdk < android.os.Build.VERSION_CODES.HONEYCOMB; 107         final boolean targetPreIcs = targetSdk < android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH; 108         final boolean targetPreL = targetSdk < android.os.Build.VERSION_CODES.LOLLIPOP; 109         final boolean targetHcNeedsOptions = context.getResources().getBoolean( 110  R.bool.target_honeycomb_needs_options_menu); 111         final boolean noActionBar = !hasFeature(FEATURE_ACTION_BAR) || hasFeature(FEATURE_NO_TITLE); 112 
113         if (targetPreHoneycomb || (targetPreIcs && targetHcNeedsOptions && noActionBar)) { 114  setNeedsMenuKey(WindowManager.LayoutParams.NEEDS_MENU_SET_TRUE); 115         } else { 116  setNeedsMenuKey(WindowManager.LayoutParams.NEEDS_MENU_SET_FALSE); 117  } 118 
119         // Non-floating windows on high end devices must put up decor beneath the system bars and 120         // therefore must know about visibility changes of those.
121         if (!mIsFloating && ActivityManager.isHighEndGfx()) { 122             if (!targetPreL && a.getBoolean( 123  R.styleable.Window_windowDrawsSystemBarBackgrounds, 124                     false)) { 125  setFlags(FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS, 126                         FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS & ~getForcedWindowFlags()); 127  } 128  } 129         if (!mForcedStatusBarColor) { 130             mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000); 131  } 132         if (!mForcedNavigationBarColor) { 133             mNavigationBarColor = a.getColor(R.styleable.Window_navigationBarColor, 0xFF000000); 134  } 135         if (a.getBoolean(R.styleable.Window_windowLightStatusBar, false)) { 136  decor.setSystemUiVisibility( 137                     decor.getSystemUiVisibility() | View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR); 138  } 139 
140         if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion 141                 >= android.os.Build.VERSION_CODES.HONEYCOMB) { 142             if (a.getBoolean( 143  R.styleable.Window_windowCloseOnTouchOutside, 144                     false)) { 145                 setCloseOnTouchOutsideIfNotSet(true); 146  } 147  } 148 
149         WindowManager.LayoutParams params = getAttributes(); 150 
151         if (!hasSoftInputMode()) { 152             params.softInputMode = a.getInt( 153  R.styleable.Window_windowSoftInputMode, 154  params.softInputMode); 155  } 156 
157         if (a.getBoolean(R.styleable.Window_backgroundDimEnabled, 158  mIsFloating)) { 159             /* All dialogs should have the window dimmed */
160             if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == 0) { 161                 params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND; 162  } 163             if (!haveDimAmount()) { 164                 params.dimAmount = a.getFloat( 165                         android.R.styleable.Window_backgroundDimAmount, 0.5f); 166  } 167  } 168 
169         if (params.windowAnimations == 0) { 170             params.windowAnimations = a.getResourceId( 171                     R.styleable.Window_windowAnimationStyle, 0); 172  } 173 
174         // The rest are only done if this window is not embedded; otherwise, 175         // the values are inherited from our container.
176         if (getContainer() == null) { 177             if (mBackgroundDrawable == null) { 178                 if (mBackgroundResource == 0) { 179                     mBackgroundResource = a.getResourceId( 180                             R.styleable.Window_windowBackground, 0); 181  } 182                 if (mFrameResource == 0) { 183                     mFrameResource = a.getResourceId(R.styleable.Window_windowFrame, 0); 184  } 185                 mBackgroundFallbackResource = a.getResourceId( 186                         R.styleable.Window_windowBackgroundFallback, 0); 187                 if (false) { 188                     System.out.println("Background: "
189                             + Integer.toHexString(mBackgroundResource) + " Frame: "
190                             + Integer.toHexString(mFrameResource)); 191  } 192  } 193             mElevation = a.getDimension(R.styleable.Window_windowElevation, 0); 194             mClipToOutline = a.getBoolean(R.styleable.Window_windowClipToOutline, false); 195             mTextColor = a.getColor(R.styleable.Window_textColor, Color.TRANSPARENT); 196  } 197 
198         // Inflate the window decor.
199 
200         int layoutResource; 201         int features = getLocalFeatures(); 202         // System.out.println("Features: 0x" + Integer.toHexString(features));
203         if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) { 204             layoutResource = R.layout.screen_swipe_dismiss; 205         } else if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) { 206             if (mIsFloating) { 207                 TypedValue res = new TypedValue(); 208  getContext().getTheme().resolveAttribute( 209                         R.attr.dialogTitleIconsDecorLayout, res, true); 210                 layoutResource = res.resourceId; 211             } else { 212                 layoutResource = R.layout.screen_title_icons; 213  } 214             // XXX Remove this once action bar supports these features.
215  removeFeature(FEATURE_ACTION_BAR); 216             // System.out.println("Title Icons!");
217         } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0
218                 && (features & (1 << FEATURE_ACTION_BAR)) == 0) { 219             // Special case for a window with only a progress bar (and title). 220             // XXX Need to have a no-title version of embedded windows.
221             layoutResource = R.layout.screen_progress; 222             // System.out.println("Progress!");
223         } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) { 224             // Special case for a window with a custom title. 225             // If the window is floating, we need a dialog layout
226             if (mIsFloating) { 227                 TypedValue res = new TypedValue(); 228  getContext().getTheme().resolveAttribute( 229                         R.attr.dialogCustomTitleDecorLayout, res, true); 230                 layoutResource = res.resourceId; 231             } else { 232                 layoutResource = R.layout.screen_custom_title; 233  } 234             // XXX Remove this once action bar supports these features.
235  removeFeature(FEATURE_ACTION_BAR); 236         } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) { 237             // If no other features and not embedded, only need a title. 238             // If the window is floating, we need a dialog layout
239             if (mIsFloating) { 240                 TypedValue res = new TypedValue(); 241  getContext().getTheme().resolveAttribute( 242                         R.attr.dialogTitleDecorLayout, res, true); 243                 layoutResource = res.resourceId; 244             } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) { 245                 layoutResource = a.getResourceId( 246  R.styleable.Window_windowActionBarFullscreenDecorLayout, 247  R.layout.screen_action_bar); 248             } else { 249                 layoutResource = R.layout.screen_title; 250  } 251             // System.out.println("Title!");
252         } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) { 253             layoutResource = R.layout.screen_simple_overlay_action_mode; 254         } else { 255             // Embedded, so no decoration is needed.
256             layoutResource = R.layout.screen_simple; 257             // System.out.println("Simple!");
258  } 259 
260  mDecor.startChanging(); 261 
262         View in = mLayoutInflater.inflate(layoutResource, null); 263         decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); 264         mContentRoot = (ViewGroup) in; 265 
266         ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT); 267         if (contentParent == null) { 268             throw new RuntimeException("Window couldn't find content container view"); 269  } 270 
271         if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) { 272             ProgressBar progress = getCircularProgressBar(false); 273             if (progress != null) { 274                 progress.setIndeterminate(true); 275  } 276  } 277 
278         if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) { 279  registerSwipeCallbacks(); 280  } 281 
282         // Remaining setup -- of background and title -- that only applies 283         // to top-level windows.
284         if (getContainer() == null) { 285             final Drawable background; 286             if (mBackgroundResource != 0) { 287                 background = getContext().getDrawable(mBackgroundResource); 288             } else { 289                 background = mBackgroundDrawable; 290  } 291  mDecor.setWindowBackground(background); 292 
293             final Drawable frame; 294             if (mFrameResource != 0) { 295                 frame = getContext().getDrawable(mFrameResource); 296             } else { 297                 frame = null; 298  } 299  mDecor.setWindowFrame(frame); 300 
301  mDecor.setElevation(mElevation); 302  mDecor.setClipToOutline(mClipToOutline); 303 
304             if (mTitle != null) { 305  setTitle(mTitle); 306  } 307 
308             if (mTitleColor == 0) { 309                 mTitleColor = mTextColor; 310  } 311  setTitleColor(mTitleColor); 312  } 313 
314  mDecor.finishChanging(); 315 
316         return contentParent; 317     }

我勒个去，这方法太挺长，不过别担忧，整体逻辑不复杂。

第4行代码getWindowStyle()是什么鬼呢？这里就直接说了，咱们在manifest文件配置的Activity的时候有时会指定theme，如：android:theme="@style/AppTheme"，getWindowStyle()就是获取咱们配置的theme信息。

接着6-199行代码都是根据咱们经过getWindowStyle()获取的theme配置信息进行相应设置。

200行代码，定义layoutResource变量。

201调用getLocalFeatures()方法又是干什么呢？咱们有时会经过代码对Activity设置一些Feature，如：requestWindowFeature(Window.FEATURE_NO_TITLE);这里getLocalFeatures()方法就是获取经过requestWindowFeature设置的一些值。

202-258根据获取的features不一样对layoutResource进行不一样的赋值，layoutResource主要纪录不一样的布局文件。若是什么也没设置，也就是说Activity没有任何修饰，那么就赋值为

R.layout.screen_simple，咱们看一下R.layout.screen_simple布局源码：

 1 <?xml version="1.0" encoding="utf-8"?>
 2 
 3 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 4     android:layout_width="match_parent"
 5     android:layout_height="match_parent"
 6     android:fitsSystemWindows="true"
 7     android:orientation="vertical">
 8     <ViewStub android:id="@+id/action_mode_bar_stub"
 9               android:inflatedId="@+id/action_mode_bar"
10               android:layout="@layout/action_mode_bar"
11               android:layout_width="match_parent"
12               android:layout_height="wrap_content"
13               android:theme="?attr/actionBarTheme" />
14     <FrameLayout 15          android:id="@android:id/content"
16          android:layout_width="match_parent"
17          android:layout_height="match_parent"
18          android:foregroundInsidePadding="false"
19          android:foregroundGravity="fill_horizontal|top"
20          android:foreground="?android:attr/windowContentOverlay" />
21 </LinearLayout>

看到了吧，很简单，就包括一个actiob_Bar,还有一个id为content的FrameLayout，而且action_Bar部分使用了布局优化ViewStub 。

继续向下分析262行将layoutResource记录的布局转化为View。

263行代码将262行生成的view添加到decor中，这个decor就是咱们上面分析过的mDecor。

264行将262行生成的View赋值给mContentRoot，用以纪录。

接下来266行经过findViewById找到ID为ID_ANDROID_CONTENT的View,这个ID_ANDROID_CONTENT又是什么鬼？经过查找最终在父类Window中找到，源码以下：

    public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;

看到了吧，就是id为content的View，以R.layout.screen_simple布局为例，最终找的就是id为content的FrameLayout。赋值给名为contentParent的ViewGroup。

最终在316行将contentParent做为generateLayout方法的返回值返回。到此generateLayout想要探讨的就都探讨完了。

咱们立刻回看上面分析的installDecor()方法第7行。将generateLayout方法返回值赋值给mContentParent，到这里，你应该知道mContentParent就是DecorView中布局为content的部分。

咱们在回看一开始分析的setContentView方法，以前分析到第7行，继续向下看直到第17行，调用mLayoutInflater.inflate(layoutResID, mContentParent)，至于inflate方法内部逻辑这里就不分析了，不是本文重点，直接说结论：mLayoutInflater.inflate(layoutResID, mContentParent)就是将layoutResID布局转化为View添加到mContentParent中。还记得mContentParent吗？它就是DecorView中id为content的View。到这里就知道了原来咱们本身定义的布局最终都是加载到这里了。

4总结

通过上面分析相信你已经有了一些眉目，咱们赶忙总结一下。

咱们平时在Activity中调用的setContentView方法其实都是调用的PhoneWindow中的setContentView方法，其首先会判断mContentParent是否为null，若是为null，则执行installDecor()方法，在installDecor()方法中会对mDecor进行判断是否为null，为null则进行初始化，mDecor为DecorView类型，DecorView继承自FrameLayout。接下来继续判断mContentParent是否为null，为null则执行generateLayout方法，在generateLayout方法中最重要的逻辑就是根据咱们设置的不一样feature找到对应布局文件，而且inflate为View，经过addView方法加入到mDecor中，而后找到布局文件中ID为content的View做为generateLayout方法最终返回值返回。接下来回到installDecor方法将generateLayout返回值赋值给mContentParent，最后回到setContentView，将咱们本身的布局文件layoutResID加载到mContentParent中。

相信通过上述分析你应该对本文一开始的那张图会有更深入的认识。