点击事件用MotionEvent来表示，当一个点击事件产生后，事件最先传递给Activity，为了搞清楚View的事件分发机制，我们首先要弄清楚Activity的构成。
1. 分析
- 首先看下setContentView如何实现的：
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
- 然后看下getWindow()：
public Window getWindow() {
return mWindow;
}
- 接着看mWindow，在Activity的attach方法中找到了mWindow：
final void attach(Context context, ActivityThread aThread,
Instrumentation instr, IBinder token, int ident,
Application application, Intent intent, ActivityInfo info,
CharSequence title, Activity parent, String id,
NonConfigurationInstances lastNonConfigurationInstances,
Configuration config, String referrer, IVoiceInteractor voiceInteractor) {
attachBaseContext(context);
mFragments.attachHost(null /*parent*/);
mWindow = new PhoneWindow(this);
...
}
说明：我们可以看到mWindow实际上是PhoneWindow，也就是getWindow方法指的就是PhoneWindow。
- 我们来看看PhoneWindow的setContentView方法（查看系统的源码网站查到的PhoneWindow）：
@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);
}
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
cb.onContentChanged();
}
}
- 接着看上面方法中的installDecor方法：
private void More ...installDecor() {
if (mDecor == null) {
mDecor = generateDecor();
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
}
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);
...
}
...
}
- 接着看generateDecor()：
protected DecorView More ...generateDecor() {
return new DecorView(getContext(), -1);
}
说明：我们发现这里创建了一个DecorView，这个是Activity的根View。
- 接着看DecorView的源码：
private final class More ...DecorView extends FrameLayout implements RootViewSurfaceTaker {
说明：发现DecorView是PhoneWindow的内部类，并且继承了FrameLayout。
- 然后我再回到installDecor方法中去看generateLayout(mDecor)做了什么：
// 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; //1
}
// 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!");
}
...
return contentParent;
说明：根据不同的情况加载不同的布局给layoutResource。
- 接着看R.layout.screen_title（上面代码注释1处）：
说明：上面的ViewStub是用来显示actionbar的。下面有两个FrameLayout：一个是title，用来显示标题，一个是content，用来显示内容。
2. 结论：
Activity的构成.png
- 一个Activity包含一个Window对象，这个对象是由PhoneWindow来实现的，PhoneWindow中又包含一个DecorView。
- PhoneWindow将DecorView作为整个应用窗口的根View，它从系统布局中加载，并且在运行时将开发人员设置给Activity的布局资源添加到系统布局的mContentParent中。
- 其中个DecorView又将屏幕划分为两个区域：一个是TitleView，一个是ContentView，我们平时所写的布局正是展示在ContentView中的。