Activity的setContentView()
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
setContentView很简单，调用了两个方法。
分析第一个方法：
getWindow().setContentView(layoutResID);
这个方法返回一个Window对象mWindow，Window是一个抽象类，它的setContentView()方法是一个抽象方法。
private Window mWindow;
public Window getWindow() {
return mWindow;
}
既然Activity用到了这个抽象的Window,在Activity里面一定有它的实例化过程。
final void attach(
//有很多参数，省略了
) {
//有很多代码，省略了
mWindow = new PhoneWindow(this, window);
}
在Activity的attach()方法里面new了一个PhoneWindow(),那么这个PhoneWindow就是Window的实现类了。
注：在不同sdk版本中Window类的实例化过程不一样，本人用的SDK版本是SDK25。从SDK23开始，Window示例是通过new PhoneWindow()方式获取的。在SDK22及之前版本，是通过PolicyManager.makeNewWindow()获取的，具体如下。
final void attach(
//有很多参数，省略了
) {
//有很多代码，省略了
mWindow = PolicyManager.makeNewWindow(this);
}
不管怎么样，最终都得到了这个PhoneWindow的实例。在PhoneWindow里面实现了setContentView()方法。
@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();//注释一：创建DecorView
} 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);
}
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
cb.onContentChanged();
}
}
在上面代码的注释一中，installDecor()方法最终会创建DecorView实例。DecorView是ViewGroup里面的一个内部类，是顶层View容器，可以查看文章最后的关系图了解。
private void installDecor() {
if (mDecor == null) {
mDecor = generateDecor();//注释1：创建DecorView.
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
}
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);//注释2:mContentParent是一个ViewGroup
// 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);
}
}
//省略很多代码
}
}
}
}
我们来看installDecor()的注释1代码：installDecor()方法调用generateDecor();创建DecorView实例。
protected DecorView generateDecor() {
return new DecorView(getContext(), -1);
}
这里new 了一个DecorView();DecorView是PhoneWindow类的内部类，继承自FrameLayout。
我们再来看看installDevor()方法的注释2代码：installDecor()方法调用generateLayout()获取mContentParent对象，它是一个ViewGroup。
protected ViewGroup generateLayout(DecorView decor) {
// Apply data from current theme.
TypedArray a = getWindowStyle();
//省略200多行代码
//填充window 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;//资源名称
}
// System.out.println("Title!");
} else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
layoutResource = R.layout.screen_simple_overlay_action_mode;//资源名称
} else {
// Embedded, so no decoration is needed.
layoutResource = R.layout.screen_simple;//资源名称
// System.out.println("Simple!");
}
mDecor.startChanging();
//将xml资源加载到LayoutInflater里面。
View in = mLayoutInflater.inflate(layoutResource, null);
//将加载了资源的View添加到DecorView中
decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
//将这个视图设为根View。
mContentRoot = (ViewGroup) in;
//获取一个Id为ID_ANDROID_CONTENT的ViewGroup,通过查看上面给出的Android系统的R.layout.screen_simple
//这个资源文件可以发现，它是一个FrameLayout。
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
if (contentParent == null) {
throw new RuntimeException("Window couldn't find content container view");
}
// 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;
}
我们查看Sdk\platforms\android-版本\data\res\layout目录下的screen_simple.xml文件。发现这个ID为content的ViewGroup是一个FrameLayout。
<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>
我们再来看下screen_simple_overlay_action_mode.xml这个文件
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true">
<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" />
<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>
发现父布局不同，一个是LinearLayout，一个是FrameLayout。
下面是Activity PhoneWindow DecorView 之间的关系图。
image.png
主要流程图：
image.png
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