深入解析Android中的setContentView加载布局原理

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，也包括我，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*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

参考链接：http://www.weyye.me/detail/framework-appcompatactivity-setcontentview/

总结

以上就是这篇文章的全部内容了，到这里setcontentview已经分析完毕，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，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，谢谢大家对的支持。