Android走进Framework之AppCompatActivity.setContentView
CorHurd
8年前
<p>今天来研究下我们最熟悉的一行代码 setContentView() 。网上也有很多关于setContentView的源码解析，但是都是基于 Activity 源码，而我们现在都是继承的 AppCompatActivity ,看源码发现改动还不少，所以我打算来研究下 AppCompatActivity 里是如何把我们的布局添加进去的。你是否也曾有过同样的疑惑，为什么创建 Activity 就要在 onCreate() 里面调用 setContentView() ?那就让我们来RTFSC (Read the fucking source code )。</p> <h2>学前疑惑</h2> <ul> <li>setContentView 中到底做了什么？为什么我们调用后就可以显示到我们想到的布局?</li> <li>PhoneWindow 是个什么鬼？ Window 和它又有什么关系？</li> <li>DecorView 什么干嘛的？和我们的布局有什么联系？</li> <li>在我们调用 requestFeature 的时候为什么要在 setContentView 之前？</li> </ul> <p>接下来，我们就来解决这些疑惑！ <strong>以下源码基于Api24</strong></p> <h2>AppCompatActivity.setContentView</h2> <p>我们先来看下 AppCompatActivity 中 setContentView 中做了什么</p> <p>AppCompatActivity.java</p> <pre> <code class="language-java">//这个是我们最常用的 @Override public void setContentView(@LayoutRes int layoutResID) { getDelegate().setContentView(layoutResID); } @Override public void setContentView(View view) { getDelegate().setContentView(view); } @Override public void setContentView(View view, ViewGroup.LayoutParams params) { getDelegate().setContentView(view, params); }</code></pre> <p>可以看到3个重载的方法都调用 getDelegate() ,而其他的方法也都是调用了 getDelegate() ,很显然这个是代理模式。那么这个 getDelegate() 返回的是什么呢？</p> <p>AppCompatActivity.java</p> <pre> <code class="language-java">/** * @return The {@link AppCompatDelegate} being used by this Activity. */ @NonNull public AppCompatDelegate getDelegate() { if (mDelegate == null) { //第一次为空，创建了AppCompatDelegate mDelegate = AppCompatDelegate.create(this, this); } return mDelegate; }</code></pre> <p>我们来看下 AppCompatDelegate 是怎么创建的</p> <p>AppCompatDelegate.java</p> <pre> <code class="language-java">private static AppCompatDelegate create(Context context, Window window, AppCompatCallback callback) { final int sdk = Build.VERSION.SDK_INT; if (BuildCompat.isAtLeastN()) { //7.0以及7.0以上创建AppCompatDelegateImplN return new AppCompatDelegateImplN(context, window, callback); } else if (sdk >= 23) { //6.0创建AppCompatDelegateImplV23 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 AppCompatDelegateImplV9(context, window, callback); } }</code></pre> <p>哦~原来根据不同的api版本返回不同的Delegate,我们先来看看 AppCompatDelegateImplN ,里面是否有 setContentView</p> <p>AppCompatDelegateImplN.java</p> <pre> <code class="language-java">@RequiresApi(24) @TargetApi(24) class AppCompatDelegateImplN extends AppCompatDelegateImplV23 { AppCompatDelegateImplN(Context context, Window window, AppCompatCallback callback) { super(context, window, callback); } @Override Window.Callback wrapWindowCallback(Window.Callback callback) { return new AppCompatWindowCallbackN(callback); } class AppCompatWindowCallbackN extends AppCompatWindowCallbackV23 { AppCompatWindowCallbackN(Window.Callback callback) { super(callback); } @Override public void onProvideKeyboardShortcuts( List<KeyboardShortcutGroup> data, Menu menu, int deviceId) { final PanelFeatureState panel = getPanelState(Window.FEATURE_OPTIONS_PANEL, true); if (panel != null && panel.menu != null) { // The menu provided is one created by PhoneWindow which we don't actually use. // Instead we'll pass through our own... super.onProvideKeyboardShortcuts(data, panel.menu, deviceId); } else { // If we don't have a menu, jump pass through the original instead super.onProvideKeyboardShortcuts(data, menu, deviceId); } } } }</code></pre> <p>发现并没有 setContentView ，那么肯定在父类。诶，它继承 AppCompatDelegateImplV23 ,而 AppCompatDelegateImplV23 又继承 AppCompatDelegateImplV14 , AppCompatDelegateImplV14 又继承 AppCompatDelegateImplV11 , AppCompatDelegateImplV11 又继承 AppCompatDelegateImplV9 ，好，知道关系后我有点懵逼了,搞什么鬼？客官别急，我们先来画个图</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/aa61c6885501cffb0339526c4d8bc049.png"></p> <p>ok,最后我在V9里找到 setContentView ，我们来看下</p> <p>AppCompatDelegateImplV9.java</p> <pre> <code class="language-java">@Override public void setContentView(int resId) { //这个很关键，稍后会讲 ensureSubDecor(); ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content); contentParent.removeAllViews(); //把我们的布局放到contentParent里面 LayoutInflater.from(mContext).inflate(resId, contentParent); mOriginalWindowCallback.onContentChanged(); } @Override public void setContentView(View v) { ensureSubDecor(); ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content); contentParent.removeAllViews(); contentParent.addView(v); mOriginalWindowCallback.onContentChanged(); } @Override public void setContentView(View v, ViewGroup.LayoutParams lp) { ensureSubDecor(); ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content); contentParent.removeAllViews(); contentParent.addView(v, lp); mOriginalWindowCallback.onContentChanged(); }</code></pre> <p>这是对应的3个实现的方法，发现都会调用 ensureSubDecor(); 并且都会找到 contentParent ，然后把我们的布局放入进去</p> <p>ok，到这里我们来捋一捋流程。</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/3807a2ddb53ac38c6d76c735fa00f4c0.png"></p> <pre> <code class="language-java">private void ensureSubDecor() { if (!mSubDecorInstalled) { //这个mSubDecor其实就ViewGroup,调用createSubDecor()后，此时存放我们的布局的容器已经准备好了 mSubDecor = createSubDecor();//核心代码！ // If a title was set before we installed the decor, propagate it now CharSequence title = getTitle(); if (!TextUtils.isEmpty(title)) { onTitleChanged(title); } applyFixedSizeWindow(); //SubDecor 安装后的回调 onSubDecorInstalled(mSubDecor); //设置标记位 mSubDecorInstalled = true; // 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_SUPPORT_ACTION_BAR); } } }</code></pre> <p>调用了 createSubDecor() ，看字面意思创建了一个 SubDecor ,看似跟 DecorView 有联系。我们看下里面做了什么操作</p> <pre> <code class="language-java">private ViewGroup createSubDecor() { TypedArray a = mContext.obtainStyledAttributes(R.styleable.AppCompatTheme); if (!a.hasValue(R.styleable.AppCompatTheme_windowActionBar)) { a.recycle(); //还记得我们使用AppCompatActivity如果不设置AppCompat主题报的错误吗？就是在这里抛出来的 throw new IllegalStateException( "You need to use a Theme.AppCompat theme (or descendant) with this activity."); } //初始化相关特征标志 if (a.getBoolean(R.styleable.AppCompatTheme_windowNoTitle, false)) { //一般我们的主题默认都是NoTitle requestWindowFeature(Window.FEATURE_NO_TITLE); } else if (a.getBoolean(R.styleable.AppCompatTheme_windowActionBar, false)) { // Don't allow an action bar if there is no title. requestWindowFeature(FEATURE_SUPPORT_ACTION_BAR); } if (a.getBoolean(R.styleable.AppCompatTheme_windowActionBarOverlay, false)) { requestWindowFeature(FEATURE_SUPPORT_ACTION_BAR_OVERLAY); } if (a.getBoolean(R.styleable.AppCompatTheme_windowActionModeOverlay, false)) { requestWindowFeature(FEATURE_ACTION_MODE_OVERLAY); } mIsFloating = a.getBoolean(R.styleable.AppCompatTheme_android_windowIsFloating, false); a.recycle(); //重点！在这里就创建DecorView,至于DecorView到底是什么以及如何创建的，稍后会讲到 mWindow.getDecorView(); final LayoutInflater inflater = LayoutInflater.from(mContext); //可以看到其实就是个ViewGroup，我们接着往下看，跟DecorView到底有啥关系 ViewGroup subDecor = null; if (!mWindowNoTitle) { //上面说了主题默认都是NoTitle，所以不会走里面的方法 if (mIsFloating) { // If we're floating, inflate the dialog title decor subDecor = (ViewGroup) inflater.inflate( R.layout.abc_dialog_title_material, null); ... } else if (mHasActionBar) { TypedValue outValue = new TypedValue(); mContext.getTheme().resolveAttribute(R.attr.actionBarTheme, outValue, true); ... // Now inflate the view using the themed context and set it as the content view subDecor = (ViewGroup) LayoutInflater.from(themedContext) .inflate(R.layout.abc_screen_toolbar, null); /** * Propagate features to DecorContentParent */ if (mOverlayActionBar) { mDecorContentParent.initFeature(FEATURE_SUPPORT_ACTION_BAR_OVERLAY); } if (mFeatureProgress) { mDecorContentParent.initFeature(Window.FEATURE_PROGRESS); } if (mFeatureIndeterminateProgress) { mDecorContentParent.initFeature(Window.FEATURE_INDETERMINATE_PROGRESS); } } } else { //我们进入else if (mOverlayActionMode) { //调用了requestWindowFeature(FEATURE_ACTION_MODE_OVERLAY)会走进来 subDecor = (ViewGroup) inflater.inflate( R.layout.abc_screen_simple_overlay_action_mode, null); } else { //ok，所以如果这些我们都没设置，默认就走到这里来了，在这里映射出了subDecor,稍后我们来看下这个布局是啥 subDecor = (ViewGroup) inflater.inflate(R.layout.abc_screen_simple, null); } ... } if (subDecor == null) { throw new IllegalArgumentException( "AppCompat does not support the current theme features: { " + "windowActionBar: " + mHasActionBar + ", windowActionBarOverlay: "+ mOverlayActionBar + ", android:windowIsFloating: " + mIsFloating + ", windowActionModeOverlay: " + mOverlayActionMode + ", windowNoTitle: " + mWindowNoTitle + " }"); } if (mDecorContentParent == null) { mTitleView = (TextView) subDecor.findViewById(R.id.title); } // Make the decor optionally fit system windows, like the window's decor ViewUtils.makeOptionalFitsSystemWindows(subDecor); //这个contentView很重要，是我们布局的父容器，你可以把它直接当成FrameLayout final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById( R.id.action_bar_activity_content); //看过相关知识的同学应该知道android.R.id.content这个Id在以前是我们布局的父容器的Id final ViewGroup windowContentView = (ViewGroup) mWindow.findViewById(android.R.id.content); if (windowContentView != null) { // There might be Views already added to the Window's content view so we need to // migrate them to our content view while (windowContentView.getChildCount() > 0) { final View child = windowContentView.getChildAt(0); windowContentView.removeViewAt(0); contentView.addView(child); } //注意！原来windowContentView的Id是android.R.id.content，现在设置成NO_ID windowContentView.setId(View.NO_ID); //在之前这个id是我们的父容器，现在将contentView设置成android.R.id.content，那么可以初步判定，这个contentView将会是我的父容器 contentView.setId(android.R.id.content); // The decorContent may have a foreground drawable set (windowContentOverlay). // Remove this as we handle it ourselves if (windowContentView instanceof FrameLayout) { ((FrameLayout) windowContentView).setForeground(null); } } // Now set the Window's content view with the decor //注意！重要！将subDecor放入到了这个Window里面，这个Window是个抽象类，其实现类是PhoneWindow，稍后会讲到 mWindow.setContentView(subDecor); .... return subDecor; }</code></pre> <p>看到了requestWindowFeature是不是很熟悉？还记得我们是怎么让Activity全屏的吗？</p> <pre> <code class="language-java">@Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); requestWindowFeature(Window.FEATURE_NO_TITLE); getWindow().setFlags(WindowManager.LayoutParams.FILL_PARENT ,WindowManager.LayoutParams.FILL_PARENT); setContentView(R.layout.activity_test); }</code></pre> <p>而且这两行代码必须在setContentView()之前调用，知道为啥了吧？因为在这里就把Window的相关特征标志给初始化了，在setContentView()之后调用就不起作用了！</p> <p>在代码里其他比较重要的地方已写了注释，我们来看下这个 abc_screen_simple.xml 的布局到底是什么样子的</p> <p>abc_screen_simple.xml</p> <pre> <code class="language-java"><android.support.v7.internal.widget.FitWindowsLinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/action_bar_root" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:fitsSystemWindows="true"> <android.support.v7.internal.widget.ViewStubCompat android:id="@+id/action_mode_bar_stub" android:inflatedId="@+id/action_mode_bar" android:layout="@layout/abc_action_mode_bar" android:layout_width="match_parent" android:layout_height="wrap_content" /> <include layout="@layout/abc_screen_content_include" /> </android.support.v7.internal.widget.FitWindowsLinearLayout></code></pre> <p>abc_screen_content_include.xml</p> <pre> <code class="language-java"><merge xmlns:android="http://schemas.android.com/apk/res/android"> <android.support.v7.internal.widget.ContentFrameLayout android:id="@id/action_bar_activity_content" android:layout_width="match_parent" android:layout_height="match_parent" android:foregroundGravity="fill_horizontal|top" android:foreground="?android:attr/windowContentOverlay" /> </merge></code></pre> <p>原来这个 subDecor 就是 FitWindowsLinearLayout</p> <p>看到这2个布局，我们先把这2个布局用图画出来。</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/36e42c8e9c5b0672c9c235232699ad11.png"></p> <p>（图不在美，能懂就行~）</p> <p>从AppCompatActivity到现在布局，在我的脑海里浮现出这样的的画面。。。</p> <p>那这是不是我们app最终的布局呢？当然不是，因为我们还没讲到非常重要的两行代码</p> <p>mWindow.getDecorView();<br> mWindow.setContentView(subDecor);</p> <p>注释中说道Window是个抽象类，其实现类是PhoneWindow。那么我们先来看PhoneWindow的getDecorView做了什么</p> <p>PhoneWindow.java</p> <pre> <code class="language-java">public class PhoneWindow extends Window implements MenuBuilder.Callback { @Override public final View getDecorView() { if (mDecor == null || mForceDecorInstall) { installDecor(); } return mDecor; } private void installDecor() { //mDecor是DecorView,第一次mDecor=null，所以调用generateDecor if (mDecor == null) { mDecor = generateDecor(); ... } //第一次mContentParent也等于null if (mContentParent == null) { //可以看到把DecorView传入进去了 mContentParent = generateLayout(mDecor); } } }</code></pre> <p>在generateDecor()做了什么？其实返回了一个DecorView对象。</p> <pre> <code class="language-java">protected DecorView generateDecor(int featureId) { // System process doesn't have application context and in that case we need to directly use // the context we have. Otherwise we want the application context, so we don't cling to the // activity. Context context; if (mUseDecorContext) { Context applicationContext = getContext().getApplicationContext(); if (applicationContext == null) { context = getContext(); } else { context = new DecorContext(applicationContext, getContext().getResources()); if (mTheme != -1) { context.setTheme(mTheme); } } } else { context = getContext(); } return new DecorView(context, featureId, this, getAttributes()); }</code></pre> <p>DecorView是啥呢？</p> <pre> <code class="language-java">public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks { ... }</code></pre> <p>哦~原来继承FrameLayout，起到了装饰的作用。</p> <p>我们在来看看 generateLayout() 做了什么。</p> <pre> <code class="language-java">protected ViewGroup generateLayout(DecorView decor) { TypedArray a = getWindowStyle(); //设置一堆标志位... ... if (!mForcedStatusBarColor) { //获取主题状态栏的颜色 mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000); } if (!mForcedNavigationBarColor) { //获取底部NavigationBar颜色 mNavigationBarColor = a.getColor(R.styleable.Window_navigationBarColor, 0xFF000000); } //获取主题一些资源 ... // Inflate the window decor. int layoutResource; int features = getLocalFeatures(); // System.out.println("Features: 0x" + Integer.toHexString(features)); if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) { ...我们设置不同的主题以及样式，会采用不同的布局文件... } else { //记住这个布局，之后我们会来验证下布局的结构 layoutResource = R.layout.screen_simple; // System.out.println("Simple!"); } //要开始更改mDecor啦~ mDecor.startChanging(); //注意，此时把screen_simple放到了DecorView里面 mDecor.onResourcesLoaded(mLayoutInflater, layoutResource); //这里的ID_ANDROID_CONTENT就是R.id.content; ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT); if (contentParent == null) { throw new RuntimeException("Window couldn't find content container view"); } ... //这里的getContainer()返回的是个Window类，也就是父Window，一般为空 if (getContainer() == null) { final Drawable background; if (mBackgroundResource != 0) { background = getContext().getDrawable(mBackgroundResource); } else { background = mBackgroundDrawable; } //设置背景 mDecor.setWindowBackground(background); final Drawable frame; if (mFrameResource != 0) { frame = getContext().getDrawable(mFrameResource); } else { frame = null; } mDecor.setWindowFrame(frame); mDecor.setElevation(mElevation); mDecor.setClipToOutline(mClipToOutline); if (mTitle != null) { setTitle(mTitle); } if (mTitleColor == 0) { mTitleColor = mTextColor; } setTitleColor(mTitleColor); } mDecor.finishChanging(); return contentParent; }</code></pre> <p>可以看到根据不同主题属性使用的不同的布局，然后返回了这个布局 contentParent 。</p> <p>我们来看看这个screen_simple.xml布局是什么样子的</p> <pre> <code class="language-java"><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" android:layout_width="match_parent" android:layout_height="match_parent" android:foregroundInsidePadding="false" android:foregroundGravity="fill_horizontal|top" android:foreground="?android:attr/windowContentOverlay" /> </LinearLayout></code></pre> <p>咦，这个布局结构跟 subDecor 好相似啊。。</p> <p>好了，到目前为止我们知道了，当我们调用 mWindow.getDecorView(); 的时候里面创建DecorView，然后又根据不同主题属性添加不同布局放到DecorView下，然后找到这个布局的 R.id.content ，也就是 mContentParent 。ok，搞清楚 mWindow.getDecorView(); 之后，我们在来看看 mWindow.setContentView(subDecor); （注意：此时把subDecor传入进去）</p> <pre> <code class="language-java">@Override public void setContentView(View view) { //调用下面的重载方法 setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT)); } @Override public void setContentView(View view, ViewGroup.LayoutParams params) { //在mWindow.getDecorView()已经创建了mContentParent if (mContentParent == null) { installDecor(); } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) { mContentParent.removeAllViews(); } //是否有transitions动画。没有，进入else if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) { view.setLayoutParams(params); final Scene newScene = new Scene(mContentParent, view); transitionTo(newScene); } else { //重要！！将这个subDecor也就是FitWindowsLinearLayout添加到这个mContentParent里面了 //mContentParent是FrameLayout，在之前设置的View.NO_ID mContentParent.addView(view, params); } mContentParent.requestApplyInsets(); final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); } mContentParentExplicitlySet = true; }</code></pre> <p>当调用了 mWindow.getDecorView(); 创建了DecorView以及 mContentParent ,并且把 subDecor 放到了 mContentParent 里面。我们再来回头看看 AppCompatDelegateImplV9 ，还记得它吗？当我们在 AppCompatActivity 的 setContentView 的时候会去调用 AppCompatDelegateImplV9 的 setContentView</p> <p>AppCompatDelegateImplV9.java</p> <pre> <code class="language-java">@Override public void setContentView(View v) { //此时DecorView和subDecor都创建好了 ensureSubDecor(); //还记得调用createSubDecor的时候把原本是R.id.content的windowContentView设置成了NO_ID //并且将contentView也就是ContentFrameLayout设置成了R.id.content吗？ //也就是说此时的contentParent就是ContentFrameLayout ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content); contentParent.removeAllViews(); //将我的布局放到contentParent里面 contentParent.addView(v); mOriginalWindowCallback.onContentChanged(); } @Override public void setContentView(int resId) { ensureSubDecor(); ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content); contentParent.removeAllViews(); //将我们的布局id映射成View并且放到contentParent下 LayoutInflater.from(mContext).inflate(resId, contentParent); mOriginalWindowCallback.onContentChanged(); } @Override public void setContentView(View v, ViewGroup.LayoutParams lp) { ensureSubDecor(); ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content); contentParent.removeAllViews(); contentParent.addView(v, lp); mOriginalWindowCallback.onContentChanged(); }</code></pre> <h2>完整布局</h2> <p>ok,看到这里，想必大家在脑海里也有个大致布局了吧，我们再来把整个app初始布局画出来</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/64adccf73efcffb27029d030e33a061b.png"></p> <h2>验证布局</h2> <p>接下来我们来验证下我们布局结构是否正确</p> <p>新建一个 Activity</p> <pre> <code class="language-java">public class TestAcitivty extends AppCompatActivity { @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_test); } }</code></pre> <p>主题</p> <pre> <code class="language-java"><!-- Base application theme. --> <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar"> <!-- Customize your theme here. --> <item name="colorPrimary">@color/colorPrimary</item> <item name="colorPrimaryDark">@color/colorPrimaryDark</item> <item name="colorAccent">@color/colorAccent</item> <item name="android:listDivider">@color/divider_dddddd</item> </style></code></pre> <p>为了演示布局非常简单，就是一个textview</p> <pre> <code class="language-java"><?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/textView" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> </TextView></code></pre> <p>运行后，我们在用 hierarchyviewer 查看下</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/e2a45385db58bc87c2b68273a829e2b4.png"></p> <p>看来我们的脑补的布局是对的！</p> <h2>学后总结</h2> <p>整个流程就是这样。看到这里我们明白了，当我们调用 setContentView 的时候加载了2次系统布局，在 PhoneWindow 里面创建了 DecorView , DecorView 是我们的最底层的View，并且将我们的布局放入到一个 ContentFrameLayout 里，我们还知道在 setContentView 的时候进行了相关特征标志初始化，所以在它之后调用 requestWindowFeature 就会不起作用然后报错。</p> <h2>setContentView时序图</h2> <p>知道这些之后我们不妨用时序图来梳理下整个调用的流程</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/58a0b19f6a042468fb2e2b7aa40e12da.jpg"></p> <p> </p> <h2>结语</h2> <p>当然，在这篇文章中，因为篇幅问题，也有许多没有讲的重要知识点，比如:</p> <ul> <li>PhoneWindow 在哪里初始化？它做了哪些事？</li> <li>view 树是如何被管理的？</li> <li>findViewById 到底是怎么找到对应的View的？</li> <li>为什么说 setContentView 在 onResume 在对用户可见？</li> <li>等等…</li> </ul> <p> </p> <p> </p> <p>来自：http://weyye.me/detail/framework-appcompatactivity-setcontentview/</p> <p> </p>