深入分析setContentView

前言

对于Android的开发者来说，setContentView大家再熟悉不过了，在我们的Activity中首先就是要用它加载我们的布局，但是应该有一部分人是不知道加载布局的原理，今天就从源码的角度分析setContentView加载布局原理。

准备工作

由于我们使用的Android API部分源码是隐藏的，当我们在AndroidStudio中是不能找到源码的，我们可以去官网下载相应源码去查看，当然在GitHub下载相应版本的API替换我们sdk下platforms相应api的android.jar。这样我们就可以在AndroidStudio查看到隐藏的api了，可以断点调试帮助我们阅读源码。

本篇文章分析源码是Android7.1（API25）。

Activiy setContentView源码分析

/**     * Set the activity content from a layout resource.  The resource will be     * inflated, adding all top-level views to the activity. */    public void setContentView(@LayoutRes int layoutResID) {        getWindow().setContentView(layoutResID);        initWindowDecorActionBar();    }

在Activity中setContentView最终调用了getWindow()的setContentView·方法，getWindow()返回的是一个Window类，它表示一个窗口的概念，我们的Activity就是一个Window，Dialog和Toast也都是通过Window来展示的，这很好理解，它是一个抽象类，具体的实现是PhoneWindow，加载布局的相关逻辑都几乎都是它处理的。

 @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();        }        mContentParentExplicitlySet = true;    }

先判断mContentParent 是否为空，当然第一次启动时mContentParent 时为空的，然后执行installDecor();方法。mContentParent不为空是通过hasFeature(FEATURE_CONTENT_TRANSITIONS)判断是否有转场动画，当没有的时候就把通过mContentParent.removeAllViews();移除mContentParent节点下的所有View.再通过inflate将我们的把布局填充到mContentParent，最后就是内容变化的回调。至于mContentParent 是什么东东，先留个悬念，稍后再说。

 private void installDecor() {        mForceDecorInstall = false;        if (mDecor == null) {            mDecor = generateDecor(-1);            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);            mDecor.setIsRootNamespace(true);            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);            }        } else {            mDecor.setWindow(this);        }        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) && !mIsStartingWindow) {                    invalidatePanelMenu(FEATURE_ACTION_BAR);                }            } else {             //设置标题                mTitleView = (TextView) findViewById(R.id.title);                if (mTitleView != null) {                    if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) {                        final View titleContainer = findViewById(R.id.title_container);                        if (titleContainer != null) {                            titleContainer.setVisibility(View.GONE);                        } else {                            mTitleView.setVisibility(View.GONE);                        }                        mContentParent.setForeground(null);                    } else {                        mTitleView.setText(mTitle);                    }                }            }            //......初始化属性变量        }    }

在上面的方法中主要工作就是初始化mDecor和mContentParent ，以及一些属性的初始化

    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());    }

generateDecor初始化一个DecorView对象，DecorView继承了FrameLayout，是我们要显示布局的顶级View，我们看到的布局，标题栏都是它里面。

然后将mDecor作为参数调用generateLayout初始化mContetParent

    protected ViewGroup generateLayout(DecorView decor) {        // Apply data from current theme.        //获取主题样式        TypedArray a = getWindowStyle();        //......省略样式的设置        // Inflate the window decor.        int layoutResource;        //获取feature并根据其来加载对应的xml布局文件        int features = getLocalFeatures();        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {            layoutResource = R.layout.screen_swipe_dismiss;        } else if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {            if (mIsFloating) {                TypedValue res = new TypedValue();                getContext().getTheme().resolveAttribute(                        R.attr.dialogTitleIconsDecorLayout, res, true);                layoutResource = res.resourceId;            } else {                layoutResource = 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 = 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(                        R.attr.dialogCustomTitleDecorLayout, res, true);                layoutResource = res.resourceId;            } else {                layoutResource = 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(                        R.attr.dialogTitleDecorLayout, res, true);                layoutResource = res.resourceId;            } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {                layoutResource = a.getResourceId(                        R.styleable.Window_windowActionBarFullscreenDecorLayout,                        R.layout.screen_action_bar);            } else {                layoutResource = R.layout.screen_title;            }            // System.out.println("Title!");        } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {            layoutResource = R.layout.screen_simple_overlay_action_mode;        } else {            // Embedded, so no decoration is needed.            layoutResource = R.layout.screen_simple;            // System.out.println("Simple!");        }        mDecor.startChanging();        mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);        if (contentParent == null) {            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);            }        }        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {            registerSwipeCallbacks();        }        // 给顶层窗口设置标题和背景        if (getContainer() == null) {            final Drawable background;            if (mBackgroundResource != 0) {                background = getContext().getDrawable(mBackgroundResource);            } else {                background = mBackgroundDrawable;            }            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;    }

代码较多，先通过getWindowStyle获取主题样式进行初始化，然后通过getLocalFeatures获取设置的不同features加载不同的布局，例如我们通常在Activity 加入requestWindowFeature(Window.FEATURE_NO_TITLE);来隐藏标题栏，不管根据Feature最终使用的是哪一种布局，里面都有一个android:id=”@android:id/content”的FrameLayout，我们的布局文件就添加到这个FrameLayout中了。我们看一下一个简单的布局

<?xml version="1.0" encoding="utf-8"?><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"              android:theme="?attr/actionBarTheme" />    <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"        android:layout_width="match_parent"         android:layout_height="0dip"        android:layout_weight="1"        android:foregroundGravity="fill_horizontal|top"        android:foreground="?android:attr/windowContentOverlay" /></LinearLayout>

通过上面的分析，你应该明白了requestWindowFeature为什么必须在setContentView之前设置了，如果在之后设置，那么通过上面的分析在setContentView执行时已经从本地读取features,而此时还没有设置，当然就无效了。

        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);        public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;

通过上面findViewById获取该对象。不过在获取ViewGroup之前还有一个重要的方法

    void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {        mStackId = getStackId();        if (mBackdropFrameRenderer != null) {            loadBackgroundDrawablesIfNeeded();            mBackdropFrameRenderer.onResourcesLoaded(                    this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,                    mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),                    getCurrentColor(mNavigationColorViewState));        }        mDecorCaptionView = createDecorCaptionView(inflater);        final View root = inflater.inflate(layoutResource, null);        if (mDecorCaptionView != null) {            if (mDecorCaptionView.getParent() == null) {                addView(mDecorCaptionView,                        new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));            }            mDecorCaptionView.addView(root,                    new ViewGroup.MarginLayoutParams(MATCH_PARENT, MATCH_PARENT));        } else {            // Put it below the color views.            addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));        }        mContentRoot = (ViewGroup) root;        initializeElevation();    }

这个比较好理解，root就是在上面判断的根据不同的features，加载的布局，然后将该布局通过addView添加到DecorView.到这里初始都成功了.

 mLayoutInflater.inflate(layoutResID, mContentParent);

在回到最初setContentView中的一句代码，如上，我们也就好理解了，它就是将我们的布局文件inflate到mContentParent中。到这里Activity的加载布局文件就完毕了。

AppCompatActivity的setContentView分析

由于AppCompatActivity的setContentView加载布局的与Activity有很多不同的地方，而且相对Activity稍微复杂点，在这里也简单分析一下。

    @Override    public void setContentView(@LayoutRes int layoutResID) {        getDelegate().setContentView(layoutResID);    }

通过名字也就知道把加载布局交给了一个委托对象。

    @NonNull    public AppCompatDelegate getDelegate() {        if (mDelegate == null) {            mDelegate = AppCompatDelegate.create(this, this);        }        return mDelegate;    }

AppCompatDelegate时一个抽象类，如下图他有几个子类实现

为啥有那么多子类呢，其实通过名字我们也能猜到，是为了兼容。为了证明这点，我们看看create方法

    private static AppCompatDelegate create(Context context, Window window,            AppCompatCallback callback) {        final int sdk = Build.VERSION.SDK_INT;        if (BuildCompat.isAtLeastN()) {            return new AppCompatDelegateImplN(context, window, callback);        } else if (sdk >= 23) {            return new AppCompatDelegateImplV23(context, window, callback);        } else if (sdk >= 14) {            return new AppCompatDelegateImplV14(context, window, callback);        } else if (sdk >= 11) {            return new AppCompatDelegateImplV11(context, window, callback);        } else {            return new AppCompatDelegateImplV9(context, window, callback);        }    }

这里就很明显了，根据不同的API版本初始化不同的delegate。通过查看代码setContentView方法的实现是在AppCompatDelegateImplV9中

    @Override    public void setContentView(int resId) {        ensureSubDecor();        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);        contentParent.removeAllViews();        LayoutInflater.from(mContext).inflate(resId, contentParent);        mOriginalWindowCallback.onContentChanged();    }

有了分析Activity的加载经验，我们就很容易明白contentParent和Activity中的mContentParent是一个东东，ensureSubDecor就是初始mSubDecor，然后removeAllViews，再将我们的布局填充到contentParent中。最后执行回调。

    private void ensureSubDecor() {        if (!mSubDecorInstalled) {            mSubDecor = createSubDecor();            //省略部分代码            onSubDecorInstalled(mSubDecor);        }    } private ViewGroup createSubDecor() {        TypedArray a = mContext.obtainStyledAttributes(R.styleable.AppCompatTheme);        //如果哦们不设置置AppCompat主题会报错，就是在这个地方        if (!a.hasValue(R.styleable.AppCompatTheme_windowActionBar)) {            a.recycle();            throw new IllegalStateException(                    "You need to use a Theme.AppCompat theme (or descendant) with this activity.");        }       //省略..... 初始化一下属性        ViewGroup subDecor = null;  //PhtoWindowgetDecorView会调用installDecor，在Activity已经介绍过，主要工作就是初始化mDecor,mContentParent。     mWindow.getDecorView();     //省略//根据设置加载不同的布局        if (!mWindowNoTitle) {            if (mIsFloating) {                // If we're floating, inflate the dialog title decor                subDecor = (ViewGroup) inflater.inflate(                        R.layout.abc_dialog_title_material, null);                // Floating windows can never have an action bar, reset the flags                mHasActionBar = mOverlayActionBar = false;            } else if (mHasActionBar) {                /**                 * This needs some explanation. As we can not use the android:theme attribute                 * pre-L, we emulate it by manually creating a LayoutInflater using a                 * ContextThemeWrapper pointing to actionBarTheme.                 */                TypedValue outValue = new TypedValue();                mContext.getTheme().resolveAttribute(R.attr.actionBarTheme, outValue, true);                Context themedContext;                if (outValue.resourceId != 0) {                    themedContext = new ContextThemeWrapper(mContext, outValue.resourceId);                } else {                    themedContext = mContext;                }                // 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);                mDecorContentParent = (DecorContentParent) subDecor                        .findViewById(R.id.decor_content_parent);                mDecorContentParent.setWindowCallback(getWindowCallback());                /**                 * 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 {            if (mOverlayActionMode) {                subDecor = (ViewGroup) inflater.inflate(                        R.layout.abc_screen_simple_overlay_action_mode, null);            } else {                subDecor = (ViewGroup) inflater.inflate(R.layout.abc_screen_simple, null);            }            if (Build.VERSION.SDK_INT >= 21) {                // If we're running on L or above, we can rely on ViewCompat's                // setOnApplyWindowInsetsListener                ViewCompat.setOnApplyWindowInsetsListener(subDecor,                        new OnApplyWindowInsetsListener() {                            @Override                            public WindowInsetsCompat onApplyWindowInsets(View v,                                    WindowInsetsCompat insets) {                                final int top = insets.getSystemWindowInsetTop();                                final int newTop = updateStatusGuard(top);                                if (top != newTop) {                                    insets = insets.replaceSystemWindowInsets(                                            insets.getSystemWindowInsetLeft(),                                            newTop,                                            insets.getSystemWindowInsetRight(),                                            insets.getSystemWindowInsetBottom());                                }                                // Now apply the insets on our view                                return ViewCompat.onApplyWindowInsets(v, insets);                            }                        });            } else {                // Else, we need to use our own FitWindowsViewGroup handling                ((FitWindowsViewGroup) subDecor).setOnFitSystemWindowsListener(                        new FitWindowsViewGroup.OnFitSystemWindowsListener() {                            @Override                            public void onFitSystemWindows(Rect insets) {                                insets.top = updateStatusGuard(insets.top);                            }                        });            }        }        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);        //contentView 是我们布局填充的地方        final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(                R.id.action_bar_activity_content);      //这个就是和我们Activity中的介绍的mDecor层级中的mContentParent是一个东西，        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);            }            // Change our content FrameLayout to use the android.R.id.content id.            // Useful for fragments.            //清除windowContentView的id            windowContentView.setId(View.NO_ID);            //将contentView的id设置成android.R.id.content，在此我们应该明白了，contentView 就成为了Activity中的mContentParent，我们的布局加载到这个view中。            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       //将subDecor 填充到DecorView中        mWindow.setContentView(subDecor);   //省略部分代码        return subDecor;    }

上面的处理逻辑就是先初始化一些主题样式，然后通过mWindow.getDecorView()初始化DecorView.和布局，然后createSubDecor根据主题加载不同的布局subDecor，通过findViewById获取contentView（ AppCompat根据不同主题加载的布局中的View R.id.action_bar_activity_content）和windowContentView （
DecorView中的View android.R.id.content）控件。获取控件后将windowContentView 的id清空，并将 contentView的id由R.id.action_bar_activity_content更改为android.R.id.content。最后通过 mWindow.setContentView(subDecor);将subDecor添加到DecorView中。

//调用两个参数方法 @Override    public void setContentView(View view) {        setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));    }//此处处理和在Activity中分析的setContentView传资源ID进行加载布局是一样的，不同的是此时mContentParent 不为空，先removeAllViews（无转场动画情况）后再直接执行mContentParent.addView(view, params);即将subDecor添加到mContentParent    @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();        }        mContentParentExplicitlySet = true;    }

关于subDecor到底是什么布局，我们随便看一个布局R.layout.abc_screen_toolbar,有标题（mWindowNoTitle为false）并且有ActionBar(mHasActionBar 为true)的情况加载的布局。

<?xml version="1.0" encoding="utf-8"?><android.support.v7.widget.ActionBarOverlayLayout        xmlns:android="http://schemas.android.com/apk/res/android"        xmlns:app="http://schemas.android.com/apk/res-auto"        android:id="@+id/decor_content_parent"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:fitsSystemWindows="true">    <include layout="@layout/abc_screen_content_include"/>    <android.support.v7.widget.ActionBarContainer            android:id="@+id/action_bar_container"            android:layout_width="match_parent"            android:layout_height="wrap_content"            android:layout_alignParentTop="true"            style="?attr/actionBarStyle"            android:touchscreenBlocksFocus="true"            android:gravity="top">        <android.support.v7.widget.Toolbar                android:id="@+id/action_bar"                android:layout_width="match_parent"                android:layout_height="wrap_content"                app:navigationContentDescription="@string/abc_action_bar_up_description"                style="?attr/toolbarStyle"/>        <android.support.v7.widget.ActionBarContextView                android:id="@+id/action_context_bar"                android:layout_width="match_parent"                android:layout_height="wrap_content"                android:visibility="gone"                android:theme="?attr/actionBarTheme"                style="?attr/actionModeStyle"/>    </android.support.v7.widget.ActionBarContainer></android.support.v7.widget.ActionBarOverlayLayout>

不管哪个主题下的布局，都会有一个id 为 abc_screen_content_include最好将id更改为androd.R,content，然后添加到mDecor中的mContentParent中。我们可以同SDK中tools下hierarchyviewer工具查看我们的布局层级结构。例如我们AppCompatActivity中setContentView传入的布局文件，是一个线程布局，该布局下有一个Button，则查看到层级结构

到这里setContentView已经分析完毕，由于水平有限，难免有错误，若在阅读时发现不妥或者错误的地方留言指正，共同进步，谢谢，Have a wonderful day。

鸣谢
Wey Ye的Android走进Framework之AppCompatActivity.setContentView