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本文出自:【Wey Ye的博客】
前言
在上一篇Android走进Framework之app是如何被启动的中讲到了从我们点击app一直到调用Activity.onCreate()
的整个流程,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 )。
学前疑惑
-
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? -
PhoneWindow
是个什么鬼?Window
和它又有什么关系? -
DecorView
什么干嘛的?和我们的布局有什么联系? - 在我们调用
requestFeature
的时候为什么要在setContentView
之前?
接下来,我们就来解决这些疑惑!以下源码基于Api24
AppCompatActivity.setContentView
我们先来看下AppCompatActivity
中setContentView
中做了什么
AppCompatActivity.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);
}
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?
AppCompatActivity.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;
}
我们来看下AppCompatDelegate
是怎么创建的
AppCompatDelegate.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);
}
}
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
AppCompatDelegateImplN.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);
}
}
}
}
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
ok,最后我在V9里找到
setContentView
,我们来看下
AppCompatDelegateImplV9.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();
}
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
ok,到这里我们来捋一捋流程。
大致流程 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);
}
}
}
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
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;
}
看到了requestWindowFeature是不是很熟悉?还记得我们是怎么让Activity全屏的吗?
@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);
}
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!
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
abc_screen_simple.xml
<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>
abc_screen_content_include.xml
<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>
原来这个subDecor
就是FitWindowsLinearLayout
看到这2个布局,我们先把这2个布局用图画出来。
布局结构(图不在美,能懂就行~)
从AppCompatActivity到现在布局,在我的脑海里浮现出这样的的画面。。。
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
mWindow.getDecorView();
mWindow.setContentView(subDecor);
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
PhoneWindow.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);
}
}
}
在generateDecor()做了什么?其实返回了一个DecorView对象。
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());
}
DecorView是啥呢?
public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
...
}
哦~原来继承FrameLayout,起到了装饰的作用。
我们在来看看generateLayout()
做了什么。
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;
}
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
。
我们来看看这个screen_simple.xml布局是什么样子的
<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>
咦,这个布局结构跟subDecor
好相似啊。。
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)
@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;
}
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
AppCompatDelegateImplV9.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();
}
完整布局
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
不喜勿喷...验证布局
接下来我们来验证下我们布局结构是否正确
新建一个Activity
public class TestAcitivty extends AppCompatActivity {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
}
}
主题
<!-- 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>
为了演示布局非常简单,就是一个textview
<?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>
运行后,我们在用hierarchyviewer
查看下
看来我们的脑补的布局是对的!
学后总结
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。
setContentView时序图
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
setContentView时序图致谢
【凯子哥带你学Framework】Activity界面显示全解析(上)
结语
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:
-
PhoneWindow
在哪里初始化?它做了哪些事? -
view
树是如何被管理的? -
findViewById
到底是怎么找到对应的View的? - 为什么说
setContentView
在onResume
在对用户可见? - 等等...
在下一篇中我会详细讲解这些问题。
最后
如果你觉得不错,点下喜欢呗~当做是对我的鼓励( _ )
文中如有错误,希望大家指出!
博主整理不易,转载请注明出处:
http://weyye.me/detail/framework-appcompatactivity-setcontentview/
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