Activity的setContentView分析
回顾下setContentView方法的流程，基于API27分析。
-
-
-
- 简单的例子
- Layout Inspector查看页面结构
- window 窗口建立
- getDecorView
- ensureSubDecor
- 添加完成
-
-
简单的例子
从一个简单的例子说起，编写一个非常简单的界面：
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:gravity="center"
tools:context=".MainActivity">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="按钮"
/>
LinearLayout>Activity中的代码:
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}Layout Inspector查看页面结构
运行起来，然后通过AndroidStudio内置的Layout Inspector查看其基本的页面结构:
非常清晰的看到DecorView是整个页面的根布局，它包含有三个子View:
LinearLayout里面的FrameLayout主要存放了ActionBar和ContentFrameLayoutnavigationBarBackground底部的操作栏背景statusBarBackground顶部的状态栏背景
其中子布局LinearLayout包含一个FrameLayout，FrameLayout包含decor_content_parent，decor_content_parent包含两个部分，一个是ActionBar，另一个就是content，类型为ContentFrameLayout，实际上继承了FrameLayout，它下面就是上面编写的LinearLayout了，因此在setContentView的时候，实际上是在这个ContentFrameLayout布局下添加的子布局。
window 窗口建立
那么DecorView的父容器是谁呢，其实是一个Window对象。通过源码来看下实际情况：
首先setContentView是调用的AppCompatActivity中的方法:
@Override
public void setContentView(@LayoutRes int layoutResID) {
getDelegate().setContentView(layoutResID);
}然后看下getDelegate()方法，实际上创建了一个AppCompatDelegate代理类：
public AppCompatDelegate getDelegate() {
if (mDelegate == null) {
mDelegate = AppCompatDelegate.create(this, this);
}
return mDelegate;
}继续看AppCompatDelegate类中的create方法:
public static AppCompatDelegate create(Activity activity, AppCompatCallback callback) {
return create(activity, activity.getWindow(), callback);
}
private static AppCompatDelegate create(Context context, Window window,
AppCompatCallback callback) {
if (Build.VERSION.SDK_INT >= 24) {
return new AppCompatDelegateImplN(context, window, callback);
} else if (Build.VERSION.SDK_INT >= 23) {
return new AppCompatDelegateImplV23(context, window, callback);
} else {
return new AppCompatDelegateImplV14(context, window, callback);
}
}这里的create方法根据不同的API等级创建了不同的代理类，其中的Window对象是通过activity.getWindow()获取的，它在Activity这个类中：
public Window getWindow() {
return mWindow;
}mWindow的赋值是在Activity类中的attach方法:
mWindow = new PhoneWindow(this, window, activityConfigCallback);继续看下PhoneWindow，实际上它继承了Window对象:
public class PhoneWindow extends Window implements MenuBuilder.Callback{
// This is the top-level view of the window, containing the window decor.
private DecorView mDecor;
public final View getDecorView() {
if (mDecor == null || mForceDecorInstall) {
installDecor();
}
return mDecor;
}
}这里就可以看到PhoneWindow中保存了DecorView的成员变量mDecor,注释也说明了DecorView是顶层View对象。
getDecorView
并且有一个getDecorView的方法，该方法其实就是生成DecorView，继续看下installDecor()方法：
private void installDecor() {
mForceDecorInstall = false;
if (mDecor == null) {
mDecor = generateDecor(-1);//生成DecorView
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);//填充mDecor
//省略代码...
} 这里面最重要的就是generateDecor(-1)和generateLayout(mDecor)，分别完成了mDecor的创建和mDecor布局的填充。
看下generateDecor(-1)方法：
protected DecorView generateDecor(int featureId) {
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());
}这个方法其实最后就是new出了一个DecorView对象。
再看generateLayout(mDecor)方法，该方法比较长，这里列出的是关键代码：
protected ViewGroup generateLayout(DecorView decor) {
//省略代码...
// 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) {
layoutResource = R.layout.screen_swipe_dismiss;
setCloseOnSwipeEnabled(true);
} 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);
//省略代码...
return contentParent;
}很明显这里根据features来确定填充的布局layoutResource是哪一个，如果没有进行特别设置，那么布局会赋值layoutResource = R.layout.screen_simple;
搜索这个布局，布局代码如下：
<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"
android:theme="?attr/actionBarTheme" />
<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>很明显这和开始使用Layout Inspector查看布局的情况一样，mDecor填充了LinearLayout布局，并且LinearLayout布局包裹了一个FrameLayout，它的id是@android:id/content.
确定好布局后，执行mDecor.onResourcesLoaded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 {
//添加布局
// Put it below the color views.
addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
mContentRoot = (ViewGroup) root;
initializeElevation();
}该方法涉及到mDecorCaptionView对象，这个应该是和多窗口有关系，默认获取出来是null，因此会走到addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));这里完成布局的填充。
ensureSubDecor
看完DecorView的生成，然后返回继续看AppCompatDelegate是如何构建的，由于不同的API版本不同，构建的代理类也不同，但是最终这些代理类共同实现了AppCompatDelegateImplV9这个类，也就是说最终getDelegate().setContentView(layoutResID);这个方法是在AppCompatDelegateImplV9这个类里调用的：
@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();
}首先看到有个ensureSubDecor()方法，该方法生成了一个mSubDecor对象，然后从mSubDecor对象中找到id为android.R.id.content的contentParent对象，然后将我们的布局id设置进去，完成填充。
那么首先看看这个ensureSubDecor方法：
private void ensureSubDecor() {
if (!mSubDecorInstalled) {
//创建mSubDecor
mSubDecor = createSubDecor();
CharSequence title = getTitle();
if (!TextUtils.isEmpty(title)) {
onTitleChanged(title);
}
applyFixedSizeWindow();
onSubDecorInstalled(mSubDecor);
mSubDecorInstalled = true;
PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
if (!isDestroyed() && (st == null || st.menu == null)) {
invalidatePanelMenu(FEATURE_SUPPORT_ACTION_BAR);
}
}
}如果mSubDecorInstalled为false的情况，也就是说之前mSubDecor不存在的时候，那么调用createSubDecor()方法，赋值给mSubDecor：
private ViewGroup createSubDecor() {
//省略代码...
//这里生成DecorView
mWindow.getDecorView();
final LayoutInflater inflater = LayoutInflater.from(mContext);
ViewGroup subDecor = null;
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);
final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
R.id.action_bar_activity_content);
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.
windowContentView.setId(View.NO_ID);
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
mWindow.setContentView(subDecor);
contentView.setAttachListener(new ContentFrameLayout.OnAttachListener() {
@Override
public void onAttachedFromWindow() {}
@Override
public void onDetachedFromWindow() {
dismissPopups();
}
});
return subDecor;
}该方法比较长，列出的是关键代码，可以看到根据mWindowNoTitle判断进行不同的布局加载，因为没有隐藏标题栏，因此mWindowNoTitle默认是false，之后判断mIsFloating，因为没有设置Dialog的主题，这里默认也是false，之后判断mHasActionBar这里默认是true，所以最终加载的布局是R.layout.abc_screen_toolbar，其布局代码：
.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">
"@layout/abc_screen_content_include"/>
.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">
.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"/>
.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"/>
.support.v7.widget.ActionBarContainer>
.support.v7.widget.ActionBarOverlayLayout> include的abc_screen_content_include布局：
"http://schemas.android.com/apk/res/android">
.support.v7.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" />
看到这里就发现这和使用Layout Inspector查看的布局是相同的。
mDecorContentParent代表的就是这个ActionBarOverlayLayout布局了。
之后
final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
R.id.action_bar_activity_content);
final ViewGroup windowContentView =
(ViewGroup) mWindow.findViewById(android.R.id.content);看看Window中它的实现：
public T findViewById(@IdRes int id) {
return getDecorView().findViewById(id);
} 很明显这里就是获取之前那个id为content的FrameLayout，如果这个windowContentView不为null的话，重新设置id:
windowContentView.setId(View.NO_ID);
contentView.setId(android.R.id.content);然后调用mWindow.setContentView(subDecor);进行和DecorView进行关联，看看PhoneWindow中的实现：
@Override
public void setContentView(View view) {
setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
@Override
public void setContentView(View view, ViewGroup.LayoutParams params) {
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;
}最终这里根据各种判断调用到了mContentParent.addView(view, params);，mContentParent就是之前那个id为content的FrameLayout了，这样就把subDecor添加进去了。
添加完成
至此ensureSubDecor()这个方法以及完成，接下来就非常简单了：
@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();
}mSubDecor获取R.id.content的布局，其实就是那个ContentFrameLayout，移除子view，然后填充布局，这样整个setContentView过程完毕了。