前言
最近想实现一下滑动返回，看了一下几个开源的滑动返回的库，或多或少都有点问题，就想自己做一下。看了一下他们的源码，发现直接被activity.getWindow().getDecorView()，activity.getWindow().getDecorView().getChildAt(0),activity.findViewById(Window.ID_ANDROID_CONTENT)整蒙了，它们具体代表一个界面的哪些区域。作为一个三年的Android开发我竟然说不清楚，好惭愧。今天就来总结一下PhoneWindow，activity.getWindow().getDecorView()，statusBar，activity.findViewById(Window.ID_ANDROID_CONTENT)等等它们的边边角角，前生今生。
分析
先谈谈window，PhoneWindow，getDecorView()
这里大部分参考自Android窗口机制（二）Window，PhoneWindow，DecorView，setContentView源码理解
Window
它是一个抽象基类，代表顶级窗口的外观及行为策略，这个类的一个实例应该被用作添加到窗口管理器的顶层视图。它提供了标准的UI策略，如背景，标题区域，默认密钥处理等。
这个抽象类的唯一现有的实现是android.view.PhoneWindow，当你需要一个Window的时候你应该实例化它。
以上是官方描述，我的理解Window就是一个窗口，最直观的表现就是一个界面的载体。
延伸一下：
那么Activity跟Window又是什么关系呢？Activity是我们开发app中打交道最多的一个类，它是一个用户交互界面。那么它怎么是一个用户交互界面呢？你不能说它是它就是，Activity的用户交互体现在setContentView(@LayoutRes int layoutResID)方法，布局xml文件就是界面展现，有布局肯定就是有界面了。使用Activity的setContentView(@LayoutRes int layoutResID)将布局文件与Activity绑定，那么它是怎么绑定的，绑定到哪去了？这里就要用到Window了，Window是一个窗口，它有一个DecorView，而DecorView就是具体承载布局文件的view，后面具体分析
PhoneWindow
它是Window的唯一实现类，也就是说Window就是一个抽象，想要具体实现，具体操作还是要靠这个PhoneWindow
getDecorView()
这个方法在Window的源码中
/**
* Retrieve the top-level window decor view (containing the standard
* window frame/decorations and the client's content inside of that), which
* can be added as a window to the window manager.
*
* <p><em>Note that calling this function for the first time "locks in"
* various window characteristics as described in
* {@link #setContentView(View, android.view.ViewGroup.LayoutParams)}.</em></p>
*
* @return Returns the top-level window decor view.
*/
public abstract View getDecorView();
这个方法是获取到顶层窗口的装饰视图（包含标准窗口框架/装饰以及其内部的客户端内容），可以将其作为窗口添加到窗口管理器。
那么什么是装饰视图DecorView呢，
/** @hide */
public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
...
DecorView(Context context, int featureId, PhoneWindow window,
WindowManager.LayoutParams params) {
super(context);
mFeatureId = featureId;
mShowInterpolator = AnimationUtils.loadInterpolator(context,
android.R.interpolator.linear_out_slow_in);
mHideInterpolator = AnimationUtils.loadInterpolator(context,
android.R.interpolator.fast_out_linear_in);
mBarEnterExitDuration = context.getResources().getInteger(
R.integer.dock_enter_exit_duration);
mForceWindowDrawsStatusBarBackground = context.getResources().getBoolean(
R.bool.config_forceWindowDrawsStatusBarBackground)
&& context.getApplicationInfo().targetSdkVersion >= N;
mSemiTransparentStatusBarColor = context.getResources().getColor(
R.color.system_bar_background_semi_transparent, null /* theme */);
updateAvailableWidth();
setWindow(window);
updateLogTag(params);
mResizeShadowSize = context.getResources().getDimensionPixelSize(
R.dimen.resize_shadow_size);
initResizingPaints();
}
...
}
在PhoneWindow里面，出现了成员变量DecorView，它是一个window的顶层视图，DecorView继承于FrameLayout，我们那些标题栏，内容栏，顶级上看是加载在DecorView上的。而DecorView则是由PhoneWindow负责添加。
setContentView
上面我们有个疑问，Activity的setContentView(@LayoutRes int layoutResID)将布局文件与Activity绑定，那么它是怎么绑定的，绑定到哪去了？这里我们就好好分析一下Activity的setContentView，说Activity是一个界面，那只是抽象的描述，具体还是要体现在布局和view上。一个Activity包含一个Window，这个Window的实例化就是PhoneWindow，PhoneWindow中又有一个DecorView，DecorView继承自FrameLayout，好了现在布局有了，往里面添加View那不就是布局和View都有了，那不就是可以组成一个完整的界面了。请看源码娓娓道来
下面是Activity的setContentView
/**
* Set the activity content from a layout resource. The resource will be
* inflated, adding all top-level views to the activity.
*
* @param layoutResID Resource ID to be inflated.
*
* @see #setContentView(android.view.View)
* @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)
*/
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
指向的是Window的setContentView
/**
* Convenience for
* {@link #setContentView(View, android.view.ViewGroup.LayoutParams)}
* to set the screen content from a layout resource. The resource will be
* inflated, adding all top-level views to the screen.
*
* @param layoutResID Resource ID to be inflated.
* @see #setContentView(View, android.view.ViewGroup.LayoutParams)
*/
public abstract void setContentView(@LayoutRes int layoutResID);
也就是PhoneWindow的具体实现
@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;
}
我们看到当mContentParent为null的时候会执行installDecor()第一次进来mContentParent肯定为null
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 {
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);
}
}
}
...
}
}
通过看installDecor的源码我们发现，这个方法中做了两件事：
生成DecorView
mDecor = generateDecor(-1);
和生成布局
mContentParent = generateLayout(mDecor);
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这个方法我们不用多看，也没什么东西，我们只需要知道生成一个DecorView的实例名字叫mDecor就行了
protected ViewGroup generateLayout(DecorView decor) {
。。。
// 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;
} 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();
}
// Remaining setup -- of background and title -- that only applies
// to top-level windows.
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;
}
generateLayout这个方法里面的东西太多，我前面删除一部分
这里layoutResource，是根据我们设置的状态栏主题，判断DecorView自动为我们加载什么样的布局。当我们将主题设置为NoTitleBar时，generateLayout方法中的layoutResource变量值为R.layout.screen_simple，所以我们看下系统这个screen_simple.xml布局文件
<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>
当拿到这个layoutResource之后，执行的是mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
//DecorView的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 {
// Put it below the color views.
addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
mContentRoot = (ViewGroup) root;
initializeElevation();
}
这里我们看到执行了一下mDecorCaptionView = createDecorCaptionView(inflater);
// Free floating overlapping windows require a caption.
private DecorCaptionView createDecorCaptionView(LayoutInflater inflater) {
DecorCaptionView decorCaptionView = null;
for (int i = getChildCount() - 1; i >= 0 && decorCaptionView == null; i--) {
View view = getChildAt(i);
if (view instanceof DecorCaptionView) {
// The decor was most likely saved from a relaunch - so reuse it.
decorCaptionView = (DecorCaptionView) view;
removeViewAt(i);
}
}
final WindowManager.LayoutParams attrs = mWindow.getAttributes();
final boolean isApplication = attrs.type == TYPE_BASE_APPLICATION ||
attrs.type == TYPE_APPLICATION || attrs.type == TYPE_DRAWN_APPLICATION;
// Only a non floating application window on one of the allowed workspaces can get a caption
if (!mWindow.isFloating() && isApplication && StackId.hasWindowDecor(mStackId)) {
// Dependent on the brightness of the used title we either use the
// dark or the light button frame.
if (decorCaptionView == null) {
decorCaptionView = inflateDecorCaptionView(inflater);
}
decorCaptionView.setPhoneWindow(mWindow, true /*showDecor*/);
} else {
decorCaptionView = null;
}
// Tell the decor if it has a visible caption.
enableCaption(decorCaptionView != null);
return decorCaptionView;
}
上面的代码我也没看懂，但是看结果是mDecorCaptionView的创建结果还是空，当mDecorCaptionView ＝= null的时候会把我们加载出来的final View root = inflater.inflate(layoutResource, null);添加到DecorView的第0个位置，也就是一个FrameLayout视图最下面，就是是把刚才那个R.layout.screen_simple文件添加到DecorView最下面,也许看下面的Hierarchy View视图更直观一些，而且我们还看到了DecorView里面有一个LinearLayout并且index为0，细心的会发现DecorView还包含了NavigationBar View 还有StatusBar View，这些东西是什么时候加进去的呢？这个先不管，也可以自己去看DecorView的源码刨根问底。
image.png
现在我们在拐回到刚才的generateLayout方法
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
其实就是执行的getDecorView().findViewById，这个东西是谁呢？就是前面加载的R.layout.screen_simple文件里面的FrameLayout android:id="@android:id/content"。最后contentParent作为generateLayout方法的返回赋值给mContentParent = generateLayout(mDecor);
/**
* Finds a view that was identified by the id attribute from the XML that
* was processed in {@link android.app.Activity#onCreate}. This will
* implicitly call {@link #getDecorView} for you, with all of the
* associated side-effects.
*
* @return The view if found or null otherwise.
*/
@Nullable
public View findViewById(@IdRes int id) {
return getDecorView().findViewById(id);
}
写了一大圈我们再回到PhoneWindow的setContentView(int layoutResID)方法，执行mLayoutInflater.inflate(layoutResID, mContentParent);将我们Activity的R.layout.activity_main布局加载到mContentParent里面去，再看下面的图也许会更清晰一些。
EF0FA9DD-9CAA-4BA2-BD0D-ED9BE3F3405C.png
回答几个问题
现在来回答几个疑问
1，activity.findViewById(Window.ID_ANDROID_CONTENT)拿到的是谁？
答：本文中拿到的是R.layout.sample布局文件的FrameLayout，其实根据不同的主题拿到不同的布局文件中的FrameLayout，它用来存放我们setContentView(id)时加载的布局
2，activity.getWindow().getDecorView().getChildAt(0)拿到的是谁？
答：本文中拿到的是R.layout.sample布局文件，其实根据不同的主题设置拿到不同的布局文件
3，statusBar在哪里？
答：在DecorView里面，可以去看上面的Hierarchy View视图，也可以自己使用Hierarchy View看自己布局的视图更直观些。
参考文章
http://blog.csdn.net/fuuckwtu/article/details/6519689
http://blog.csdn.net/yanbober/article/details/45970721
http://blog.csdn.net/mr_liabill/article/details/49534851
http://www.jianshu.com/p/983eb8d5bb1a
http://www.jianshu.com/p/afa921d8ed24
http://blog.csdn.net/hohohong/article/details/54412464
网友评论