从setContentView()谈起
本文主要讲解View或者ViewGroup是如何添加到应用程序的窗口中的。
1. 最简单的Activity
一个Activity最简单的结构是如下：
public class MainActivity extends Activity {
private Button taskSwitch;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//那就从这个setContentView开启我们的View或者ViewGroup加载之旅吧
setContentView(R.layout.activity_main);
}
}
R.layout.activity_main.xml结构如下：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<Button android:id="@+id/taskSwitch"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/taskSwitch"/>
</RelativeLayout>
2. setContentView关键流程顺序图
Step1 Activity.setContentView()
这个方法是Activity里面的方法，直接回调了Window的getContentView(),而mWindow对象实际上是PhoneWindow对象。
frameworks/base/core/java/android/app/Activity.java
public class Activity extends ContextThemeWrapper
implements LayoutInflater.Factory2,
Window.Callback, KeyEvent.Callback,
OnCreateContextMenuListener, ComponentCallbacks2 {
public void setContentView(int layoutResID) {
getWindow().setContentView(layoutResID);
}
public Window getWindow() {
return mWindow; //Window对象，实际上是一个PhoneWindow对象，它是在AMS初始化的时候创建的
}
}
AMS初始化的时候会调用PolicyManager.makeNewWindow(this);
public class Activity extends ContextThemeWrapper
implements LayoutInflater.Factory2,
Window.Callback, KeyEvent.Callback,
OnCreateContextMenuListener, ComponentCallbacks2 {
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) {
attachBaseContext(context);
mFragments.attachActivity(this, mContainer, null);
mWindow = PolicyManager.makeNewWindow(this); //这里创建的实际上是PhoneWindow对象
mWindow.setCallback(this);
mWindow.getLayoutInflater().setPrivateFactory(this);
……
}
}
而PolicyManager是调用的IPolicy的接口实现穿件Window的。
public final class PolicyManager {
private static final String POLICY_IMPL_CLASS_NAME =
"com.android.internal.policy.impl.Policy";
private static final IPolicy sPolicy;
……
public static Window makeNewWindow(Context context) {
return sPolicy.makeNewWindow(context);
}
……
}
frameworks/base/policy/src/com/android/internal/policy/impl/Policy.java实现了IPolicy接口，创建了Window对象，实际上是PhoneWindow对象
// Simple implementation of the policy interface that spawns the right
// set of objects
public class Policy implements IPolicy {
private static final String TAG = "PhonePolicy";
……
public Window makeNewWindow(Context context) {
return new PhoneWindow(context); //创建了Window对象，实际上是PhoneWindow对象
}
}
到此，我们知道Activity.setContentView()最终调用到的是PhoneWindow.setContentView()。
Step2 PhoneWindow.setContentView()
如果第一次调用mDecor和mContentParent对象都为null，会调用installDecor()，如果不是，则调用mContentParent.removeAllViews()来删除所有的子View，然后inflate所以的View，再添加到mContentParent中。
public class PhoneWindow extends Window implements MenuBuilder.Callback {
@Override
public void setContentView(int layoutResID) {
//如果第一次调用mDecor和mContentParent对象都为null，会调用installDecor()，如果不是，则调用mContentParent.removeAllViews()
if (mContentParent == null) {
installDecor();
} else {
mContentParent.removeAllViews();
}
mLayoutInflater.inflate(layoutResID, mContentParent);
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
cb.onContentChanged();
}
}
}
Step2.1 PhoneWindow. installDecor()
public class PhoneWindow extends Window implements MenuBuilder.Callback {
private void 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);
// Set up decor part of UI to ignore fitsSystemWindows if appropriate.
mDecor.makeOptionalFitsSystemWindows();
mTitleView = (TextView)findViewById(com.android.internal.R.id.title);
if (mTitleView != null) {
mTitleView.setLayoutDirection(mDecor.getLayoutDirection());
if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) {
View titleContainer = findViewById(com.android.internal.R.id.title_container);
if (titleContainer != null) {
titleContainer.setVisibility(View.GONE);
} else {
mTitleView.setVisibility(View.GONE);
}
if (mContentParent instanceof FrameLayout) {
((FrameLayout)mContentParent).setForeground(null);
}
} else {
mTitleView.setText(mTitle);
}
} else {
mActionBar = (ActionBarView) findViewById(com.android.internal.R.id.action_bar);
if (mActionBar != null) {
mActionBar.setWindowCallback(getCallback());
if (mActionBar.getTitle() == null) {
mActionBar.setWindowTitle(mTitle);
}
final int localFeatures = getLocalFeatures();
if ((localFeatures & (1 << FEATURE_PROGRESS)) != 0) {
mActionBar.initProgress();
}
if ((localFeatures & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {
mActionBar.initIndeterminateProgress();
}
final ActionBarOverlayLayout abol = (ActionBarOverlayLayout) findViewById(
com.android.internal.R.id.action_bar_overlay_layout);
if (abol != null) {
abol.setOverlayMode(
(localFeatures & (1 << FEATURE_ACTION_BAR_OVERLAY)) != 0);
}
boolean splitActionBar = false;
final boolean splitWhenNarrow =
(mUiOptions & ActivityInfo.UIOPTION_SPLIT_ACTION_BAR_WHEN_NARROW) != 0;
if (splitWhenNarrow) {
splitActionBar = getContext().getResources().getBoolean(
com.android.internal.R.bool.split_action_bar_is_narrow);
} else {
splitActionBar = getWindowStyle().getBoolean(
com.android.internal.R.styleable.Window_windowSplitActionBar, false);
}
final ActionBarContainer splitView = (ActionBarContainer) findViewById(
com.android.internal.R.id.split_action_bar);
if (splitView != null) {
mActionBar.setSplitView(splitView);
mActionBar.setSplitActionBar(splitActionBar);
mActionBar.setSplitWhenNarrow(splitWhenNarrow);
final ActionBarContextView cab = (ActionBarContextView) findViewById(
com.android.internal.R.id.action_context_bar);
cab.setSplitView(splitView);
cab.setSplitActionBar(splitActionBar);
cab.setSplitWhenNarrow(splitWhenNarrow);
} else if (splitActionBar) {
Log.e(TAG, "Requested split action bar with " +
"incompatible window decor! Ignoring request.");
}
if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) != 0 ||
(mIconRes != 0 && !mActionBar.hasIcon())) {
mActionBar.setIcon(mIconRes);
} else if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) == 0 &&
mIconRes == 0 && !mActionBar.hasIcon()) {
mActionBar.setIcon(
getContext().getPackageManager().getDefaultActivityIcon());
mResourcesSetFlags |= FLAG_RESOURCE_SET_ICON_FALLBACK;
}
if ((mResourcesSetFlags & FLAG_RESOURCE_SET_LOGO) != 0 ||
(mLogoRes != 0 && !mActionBar.hasLogo())) {
mActionBar.setLogo(mLogoRes);
}
// Post the panel invalidate for later; avoid application onCreateOptionsMenu
// being called in the middle of onCreate or similar.
mDecor.post(new Runnable() {
public void run() {
// Invalidate if the panel menu hasn't been created before this.
PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
if (!isDestroyed() && (st == null || st.menu == null)) {
invalidatePanelMenu(FEATURE_ACTION_BAR);
}
}
});
}
}
}
}
}
首先判断mDecor是否为空，如果是空，则调用generateDecor()创建一个新的DecorView赋值给mDecor，该类是一个FrameLayout的子类，是一个ViewGroup，当用HierarchyViewer查看Layoutt的时候每个窗口最顶层都有的一个FrameLayout，这个FrameLayout就是这边的这个DecorView。
protected DecorView generateDecor() {
return new DecorView(getContext(), -1);
}
private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {
}
然后判断mContentParent是否为空，如果为空，则调用generateLayout(mDecor)创建mContentParent。
protected ViewGroup generateLayout(DecorView decor) {
// Apply data from current theme.
// 1. 从com.android.internal.R.styleable.Window也就是android：theme=“”配置的值中获取Window的Style属性
// 2. 通过requestFeature方法设置Window.mFeatures和PhoneWindow.mLocalFeatures属性，设置宽口风格
TypedArray a = getWindowStyle();
if (false) {
System.out.println("From style:");
String s = "Attrs:";
for (int i = 0; i < com.android.internal.R.styleable.Window.length; i++) {
s = s + " " + Integer.toHexString(com.android.internal.R.styleable.Window[i]) + "="
+ a.getString(i);
}
System.out.println(s);
}
mIsFloating = a.getBoolean(com.android.internal.R.styleable.Window_windowIsFloating, false);
int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)
& (~getForcedWindowFlags());
if (mIsFloating) {
setLayout(WRAP_CONTENT, WRAP_CONTENT);
setFlags(0, flagsToUpdate);
} else {
setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);
}
if (a.getBoolean(com.android.internal.R.styleable.Window_windowNoTitle, false)) {
requestFeature(FEATURE_NO_TITLE);
} else if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionBar, false)) {
// Don't allow an action bar if there is no title.
requestFeature(FEATURE_ACTION_BAR);
}
if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionBarOverlay, false)) {
requestFeature(FEATURE_ACTION_BAR_OVERLAY);
}
if (a.getBoolean(com.android.internal.R.styleable.Window_windowActionModeOverlay, false)) {
requestFeature(FEATURE_ACTION_MODE_OVERLAY);
}
if (a.getBoolean(com.android.internal.R.styleable.Window_windowFullscreen, false)) {
setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));
}
if (a.getBoolean(com.android.internal.R.styleable.Window_windowTranslucentStatus,
false)) {
setFlags(FLAG_TRANSLUCENT_STATUS, FLAG_TRANSLUCENT_STATUS
& (~getForcedWindowFlags()));
}
if (a.getBoolean(com.android.internal.R.styleable.Window_windowTranslucentNavigation,
false)) {
setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION
& (~getForcedWindowFlags()));
}
if (a.getBoolean(com.android.internal.R.styleable.Window_windowOverscan, false)) {
setFlags(FLAG_LAYOUT_IN_OVERSCAN, FLAG_LAYOUT_IN_OVERSCAN&(~getForcedWindowFlags()));
}
if (a.getBoolean(com.android.internal.R.styleable.Window_windowShowWallpaper, false)) {
setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags()));
}
if (a.getBoolean(com.android.internal.R.styleable.Window_windowEnableSplitTouch,
getContext().getApplicationInfo().targetSdkVersion
>= android.os.Build.VERSION_CODES.HONEYCOMB)) {
setFlags(FLAG_SPLIT_TOUCH, FLAG_SPLIT_TOUCH&(~getForcedWindowFlags()));
}
a.getValue(com.android.internal.R.styleable.Window_windowMinWidthMajor, mMinWidthMajor);
a.getValue(com.android.internal.R.styleable.Window_windowMinWidthMinor, mMinWidthMinor);
if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedWidthMajor)) {
if (mFixedWidthMajor == null) mFixedWidthMajor = new TypedValue();
a.getValue(com.android.internal.R.styleable.Window_windowFixedWidthMajor,
mFixedWidthMajor);
}
if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedWidthMinor)) {
if (mFixedWidthMinor == null) mFixedWidthMinor = new TypedValue();
a.getValue(com.android.internal.R.styleable.Window_windowFixedWidthMinor,
mFixedWidthMinor);
}
if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedHeightMajor)) {
if (mFixedHeightMajor == null) mFixedHeightMajor = new TypedValue();
a.getValue(com.android.internal.R.styleable.Window_windowFixedHeightMajor,
mFixedHeightMajor);
}
if (a.hasValue(com.android.internal.R.styleable.Window_windowFixedHeightMinor)) {
if (mFixedHeightMinor == null) mFixedHeightMinor = new TypedValue();
a.getValue(com.android.internal.R.styleable.Window_windowFixedHeightMinor,
mFixedHeightMinor);
}
// 3.读取SDK版本信息
final Context context = getContext();
final int targetSdk = context.getApplicationInfo().targetSdkVersion;
final boolean targetPreHoneycomb = targetSdk < android.os.Build.VERSION_CODES.HONEYCOMB;
final boolean targetPreIcs = targetSdk < android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH;
final boolean targetHcNeedsOptions = context.getResources().getBoolean(
com.android.internal.R.bool.target_honeycomb_needs_options_menu);
final boolean noActionBar = !hasFeature(FEATURE_ACTION_BAR) || hasFeature(FEATURE_NO_TITLE);
if (targetPreHoneycomb || (targetPreIcs && targetHcNeedsOptions && noActionBar)) {
addFlags(WindowManager.LayoutParams.FLAG_NEEDS_MENU_KEY);
} else {
clearFlags(WindowManager.LayoutParams.FLAG_NEEDS_MENU_KEY);
}
if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion
>= android.os.Build.VERSION_CODES.HONEYCOMB) {
if (a.getBoolean(
com.android.internal.R.styleable.Window_windowCloseOnTouchOutside,
false)) {
setCloseOnTouchOutsideIfNotSet(true);
}
}
// 4. 获取LayoutParams信息用来判断是否输入法、是否模糊后面的，是否有窗口动画
WindowManager.LayoutParams params = getAttributes();
if (!hasSoftInputMode()) {
params.softInputMode = a.getInt(
com.android.internal.R.styleable.Window_windowSoftInputMode,
params.softInputMode);
}
if (a.getBoolean(com.android.internal.R.styleable.Window_backgroundDimEnabled,
mIsFloating)) {
/* All dialogs should have the window dimmed */
if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == 0) {
params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND;
}
if (!haveDimAmount()) {
params.dimAmount = a.getFloat(
android.R.styleable.Window_backgroundDimAmount, 0.5f);
}
}
if (params.windowAnimations == 0) {
params.windowAnimations = a.getResourceId(
com.android.internal.R.styleable.Window_windowAnimationStyle, 0);
}
// The rest are only done if this window is not embedded; otherwise,
// the values are inherited from our container.
if (getContainer() == null) {
if (mBackgroundDrawable == null) {
if (mBackgroundResource == 0) {
mBackgroundResource = a.getResourceId(
com.android.internal.R.styleable.Window_windowBackground, 0);
}
if (mFrameResource == 0) {
mFrameResource = a.getResourceId(com.android.internal.R.styleable.Window_windowFrame, 0);
}
if (false) {
System.out.println("Background: "
+ Integer.toHexString(mBackgroundResource) + " Frame: "
+ Integer.toHexString(mFrameResource));
}
}
mTextColor = a.getColor(com.android.internal.R.styleable.Window_textColor, 0xFF000000);
}
// Inflate the window decor.
// 5. 获取上面设置的PhoneWindow.mLocalFeatures，根据一些列的条件判断需要是哪个layoutResource，比如是否是全屏，是否有标题栏
// 有如下7种类型的layout：
// com.android.internal.R.layout.screen_title_icons
// com.android.internal.R.layout.screen_progress
// com.android.internal.R.layout.screen_custom_title
// com.android.internal.R.layout.screen_action_bar
// com.android.internal.R.layout.screen_title
// com.android.internal.R.layout.screen_simple_overlay_action_mode
// com.android.internal.R.layout.screen_simple
int layoutResource;
int features = getLocalFeatures();
// System.out.println("Features: 0x" + Integer.toHexString(features));
if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {
if (mIsFloating) {
TypedValue res = new TypedValue();
getContext().getTheme().resolveAttribute(
com.android.internal.R.attr.dialogTitleIconsDecorLayout, res, true);
layoutResource = res.resourceId;
} else {
layoutResource = com.android.internal.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 = com.android.internal.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(
com.android.internal.R.attr.dialogCustomTitleDecorLayout, res, true);
layoutResource = res.resourceId;
} else {
layoutResource = com.android.internal.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(
com.android.internal.R.attr.dialogTitleDecorLayout, res, true);
layoutResource = res.resourceId;
} else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
layoutResource = com.android.internal.R.layout.screen_action_bar;
} else {
layoutResource = com.android.internal.R.layout.screen_title;
}
// System.out.println("Title!");
} else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
layoutResource = com.android.internal.R.layout.screen_simple_overlay_action_mode;
} else {
// Embedded, so no decoration is needed.
layoutResource = com.android.internal.R.layout.screen_simple;
// System.out.println("Simple!");
}
mDecor.startChanging();
// 6. 填充相应的layoutResource，并把它加到decor里面
View in = mLayoutInflater.inflate(layoutResource, null);
decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
// 7. 找出相应的ID_ANDROID_CONTENT的ViewGroup，实际想就是上面layoutResource里面的<FrameLayout android:id="@android:id/content" /> 这个FrameLayout
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);
}
}
// Remaining setup -- of background and title -- that only applies
// to top-level windows.
if (getContainer() == null) {
Drawable drawable = mBackgroundDrawable;
if (mBackgroundResource != 0) {
drawable = getContext().getResources().getDrawable(mBackgroundResource);
}
mDecor.setWindowBackground(drawable);
drawable = null;
if (mFrameResource != 0) {
drawable = getContext().getResources().getDrawable(mFrameResource);
}
mDecor.setWindowFrame(drawable);
// System.out.println("Text=" + Integer.toHexString(mTextColor) +
// " Sel=" + Integer.toHexString(mTextSelectedColor) +
// " Title=" + Integer.toHexString(mTitleColor));
if (mTitleColor == 0) {
mTitleColor = mTextColor;
}
if (mTitle != null) {
setTitle(mTitle);
}
setTitleColor(mTitleColor);
}
mDecor.finishChanging();
return contentParent;
}
此时，我们拿一个常用的com.android.internal.R.layout.screen_title窗口布局文件来分析一下。
这个窗口布局文件分为3个部分：
action mode 标题栏内容区域 Activity的SetContentView的Layout文件实际放置的俯视图就是这个id为conten的FrameLayout
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:fitsSystemWindows="true"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<!-- Popout bar for action modes -->
<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" />
<RelativeLayout android:id="@android:id/title_container"
style="?android:attr/windowTitleBackgroundStyle"
android:layout_width="match_parent"
android:layout_height="?android:attr/windowTitleSize">
<!-- The title background has 9px left padding. -->
<ImageView android:id="@android:id/left_icon"
android:visibility="gone"
android:layout_marginEnd="9dip"
android:layout_width="16dip"
android:layout_height="16dip"
android:scaleType="fitCenter"
android:layout_alignParentStart="true"
android:layout_centerVertical="true" />
<ProgressBar android:id="@+id/progress_circular"
style="?android:attr/progressBarStyleSmallTitle"
android:visibility="gone"
android:max="10000"
android:layout_centerVertical="true"
android:layout_alignParentEnd="true"
android:layout_marginStart="6dip"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<!-- There are 6dip between this and the circular progress on the right, we
also make 6dip (with the -3dip margin_left) to the icon on the left or
the screen left edge if no icon. This also places our left edge 3dip to
the left of the title text left edge. -->
<ProgressBar android:id="@+id/progress_horizontal"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="-3dip"
android:layout_toStartOf="@android:id/progress_circular"
android:layout_toEndOf="@android:id/left_icon"
android:layout_centerVertical="true"
android:visibility="gone"
android:max="10000" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:layout_toStartOf="@id/progress_circular"
android:layout_toEndOf="@android:id/left_icon"
>
<TextView android:id="@android:id/title"
style="?android:attr/windowTitleStyle"
android:layout_width="0dip"
android:layout_height="match_parent"
android:layout_weight="1"
android:background="@null"
android:fadingEdge="horizontal"
android:scrollHorizontally="true"
android:gravity="center_vertical"
android:layout_marginEnd="2dip"
/>
<!-- 2dip between the icon and the title text, if icon is present. -->
<ImageView android:id="@android:id/right_icon"
android:visibility="gone"
android:layout_width="16dip"
android:layout_height="16dip"
android:layout_weight="0"
android:layout_gravity="center_vertical"
android:scaleType="fitCenter"
/>
</LinearLayout>
</RelativeLayout>
<FrameLayout android:id="@android:id/content"
android:layout_width="match_parent"
android:layout_height="0dip"
android:layout_weight="1"
android:foregroundGravity="fill_horizontal|top"
android:foreground="?android:attr/windowContentOverlay" />
</LinearLayout>
Step2.2 LayoutInflater.inflate()
前一步结束之后，我们需要的mDecor和mContentParent都已经初始化完毕，mContentParent（
public View inflate(int resource, ViewGroup root) {
return inflate(resource, root, root != null);
}
public View inflate(XmlPullParser parser, ViewGroup root) {
return inflate(parser, root, root != null);
}
public View inflate(int resource, ViewGroup root, boolean attachToRoot) {
if (DEBUG) System.out.println("INFLATING from resource: " + resource);
XmlResourceParser parser = getContext().getResources().getLayout(resource);
try {
return inflate(parser, root, attachtoroot);
} finally {
parser.close();
}
}
public view inflate(xmlpullparser parser, viewgroup root, boolean attachtoroot) {
synchronized (mconstructorargs) {
trace.tracebegin(trace.trace_tag_view, "inflate");
final attributeset attrs = xml.asattributeset(parser);
context lastcontext = (context)mconstructorargs[0];
mconstructorargs[0] = mcontext;
view result = root;
try {
// 1. 查找并初始化跟试图节点
// look for the root node.
……
final string name = parser.getname();
if (tag_merge.equals(name)) {
if (root == null || !attachtoroot) {
throw new inflateexception("<merge /> can be used only with a valid "
+ "viewgroup root and attachtoroot=true");
}
rinflate(parser, root, attrs, false);
} else {
// temp is the root view that was found in the xml
view temp;
if (tag_1995.equals(name)) {
temp = new blinklayout(mcontext, attrs);
} else {
temp = createviewfromtag(root, name, attrs);
}
viewgroup.layoutparams params = null;
if (root != null) {
if (debug) {
system.out.println("creating params from root: " +
root);
}
// create layout params that match root, if supplied
params = root.generatelayoutparams(attrs);
if (!attachtoroot) {
// set the layout params for temp if we are not
// attaching. (if we are, we use addview, below)
temp.setlayoutparams(params);
}
}
if (debug) {
system.out.println("-----> start inflating children");
}
// 创建所有的子试图节点
// inflate all children under temp
rinflate(parser, temp, attrs, true);
……
}
} catch (xmlpullparserexception e) {
inflateexception ex = new inflateexception(e.getmessage());
ex.initcause(e);
throw ex;
} catch (ioexception e) {
inflateexception ex = new inflateexception(
parser.getpositiondescription()
+ ": " + e.getmessage());
ex.initcause(e);
throw ex;
} finally {
// don't retain static reference on context.
mconstructorargs[0] = lastcontext;
mconstructorargs[1] = null;
}
trace.traceend(trace.trace_tag_view);
return result;
}
}
实际上mLayoutInflater实际上是PhoneLayoutInflater的对象，可以分析Step1中PhoneWindow的初始化过程得知。可以看如下代码：
public class PhoneWindow extends Window implements MenuBuilder.Callback {
public PhoneWindow(Context context) {
super(context);
mLayoutInflater = LayoutInflater.from(context);
}
}
public abstract class LayoutInflater {
public static LayoutInflater from(Context context) {
LayoutInflater LayoutInflater =
(LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (LayoutInflater == null) {
throw new AssertionError("LayoutInflater not found.");
}
return LayoutInflater;
}
}
class ContextImpl extends Context {
static {
registerService(LAYOUT_INFLATER_SERVICE, new ServiceFetcher() {
public Object createService(ContextImpl ctx) {
return PolicyManager.makeNewLayoutInflater(ctx.getOuterContext());
}});
}
private static final HashMap<String, ServiceFetcher> SYSTEM_SERVICE_MAP =
new HashMap<String, ServiceFetcher>();
private static int sNextPerContextServiceCacheIndex = 0;
private static void registerService(String serviceName, ServiceFetcher fetcher) {
if (!(fetcher instanceof StaticServiceFetcher)) {
fetcher.mContextCacheIndex = sNextPerContextServiceCacheIndex++;
}
SYSTEM_SERVICE_MAP.put(serviceName, fetcher);
}
public Object getSystemService(String name) {
ServiceFetcher fetcher = SYSTEM_SERVICE_MAP.get(name);
return fetcher == null ? null : fetcher.getService(this);
}
}
public final class PolicyManager {
private static final String POLICY_IMPL_CLASS_NAME =
"com.android.internal.policy.impl.Policy";
private static final IPolicy sPolicy;
static {
// Pull in the actual implementation of the policy at run-time
try {
Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
sPolicy = (IPolicy)policyClass.newInstance();
}
……
}
public static LayoutInflater makeNewLayoutInflater(Context context) {
return sPolicy.makeNewLayoutInflater(context);
}
}
public class Policy implements IPolicy {
public LayoutInflater makeNewLayoutInflater(Context context) {
return new PhoneLayoutInflater(context);
}
}
至此，总的流程都已经结束了，我们的Acitivity.setContentView就差不多分析完毕了。总的来说上面的过程可以概括为3步：
1、创建一个DecorView对象，该对象将作为整个应用窗口的根视图
2、创建不同的窗口布局文件，并且获取Activity的布局文件该存放的地方，即该窗口布局文件内id为content的FrameLayout指定（） 。
3、将Activity的布局文件添加至id为content的FrameLayout内。
3、将Activity的布局文件添加至id为content的FrameLayout内。
3. 最后我们来分析一下每一个View或者ViewGroup是如何被创建的。
从上面我们可以得知，每一个View或者ViewGroup都是通过调用LayoutInflater.createviewfromtag()来进行View的穿件
View createViewFromTag(View parent, String name, AttributeSet attrs) {
if (name.equals("view")) {
name = attrs.getAttributeValue(null, "class");
}
if (DEBUG) System.out.println("******** Creating view: " + name);
try {
View view;
// 此处几个Factory都不会执行
if (mFactory2 != null) view = mFactory2.onCreateView(parent, name, mContext, attrs);
else if (mFactory != null) view = mFactory.onCreateView(name, mContext, attrs);
else view = null;
if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, mContext, attrs);
}
if (view == null) {
// 根据View是否是内置判断需要调用的方法：
// 如果是内置的（android.widget或android.webkit或andriod.view包里的）android自身类就调用LayoutInflater.onCreateView (3parameters)，如果不是就调用LayoutInflater.createView
如果不是内置（自定义的，或者目录不在上述几个包中的）则调用LayoutInflater.createView(name, null, attrs);
if (-1 == name.indexOf('.')) {
view = onCreateView(parent, name, attrs);
} else {
view = createView(name, null, attrs);
}
}
if (DEBUG) System.out.println("Created view is: " + view);
return view;
……
}
根据View是否是内置判断需要调用的方法：
如果是内置的（android.widget或android.webkit或andriod.view包里的）android自身类就调用LayoutInflater.onCreateView (3parameters)，如果不是就调用LayoutInflater.createView；
如果不是内置（自定义的，或者目录不在上述几个包中的）则调用LayoutInflater.createView(name, null, attrs);
如果是内置的（android.widget或android.webkit）android自身类就调用LayoutInflater.createView，如果不是就调用LayoutInflater.onCreateView(2 parameters)；
public abstract class LayoutInflater {
protected View onCreateView(String name, AttributeSet attrs)
throws ClassNotFoundException {
return createView(name, "android.view.", attrs);
}
protected View onCreateView(View parent, String name, AttributeSet attrs)
throws ClassNotFoundException {
// 1. 根据多态性，直接调用PhoneLayoutInflater.onCreateView(2 parameters)
return onCreateView(name, attrs);
}
}
public class PhoneLayoutInflater extends LayoutInflater {
private static final String[] sClassPrefixList = {
"android.widget.",
"android.webkit."
};
@Override protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException {
// 2. 如果是内置的（android.widget或android.webkit）android自身类就调用LayoutInflater.createView，如果不是就调用LayoutInflater.onCreateView(2 parameters)
for (String prefix : sClassPrefixList) {
try {
View view = createView(name, prefix, attrs);
if (view != null) {
return view;
}
} catch (ClassNotFoundException e) {
// In this case we want to let the base class take a crack
// at it.
}
}
// 2.
return super.onCreateView(name, attrs);
}
}
不过最终都是要调用createView()方法来进行View或者ViewGroup的创建。createView()的方法气势很简答，就是通过反射机制把View或者ViewGroup给创建出来。
public final View createView(String name, String prefix, AttributeSet attrs)
throws ClassNotFoundException, InflateException {
// 1. 如果sConstructorMap里面已经有对应的类，则直接取出来，
// 如果没有，则通过发射机制把对应的类给loadClass进来；
Constructor<? extends View> constructor = sConstructorMap.get(name);
Class<? extends View> clazz = null;
try {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, name);
if (constructor == null) {
// Class not found in the cache, see if it's real, and try to add it
clazz = mContext.getClassLoader().loadClass(
prefix != null ? (prefix + name) : name).asSubclass(View.class);
if (mFilter != null && clazz != null) {
boolean allowed = mFilter.onLoadClass(clazz);
if (!allowed) {
failNotAllowed(name, prefix, attrs);
}
}
constructor = clazz.getConstructor(mConstructorSignature);
sConstructorMap.put(name, constructor);
} else {
// If we have a filter, apply it to cached constructor
if (mFilter != null) {
// Have we seen this name before?
Boolean allowedState = mFilterMap.get(name);
if (allowedState == null) {
// New class -- remember whether it is allowed
clazz = mContext.getClassLoader().loadClass(
prefix != null ? (prefix + name) : name).asSubclass(View.class);
boolean allowed = clazz != null && mFilter.onLoadClass(clazz);
mFilterMap.put(name, allowed);
if (!allowed) {
failNotAllowed(name, prefix, attrs);
}
} else if (allowedState.equals(Boolean.FALSE)) {
failNotAllowed(name, prefix, attrs);
}
}
}
Object[] args = mConstructorArgs;
args[1] = attrs;
// 2. 创建对应的View或者ViewGroup对象。
constructor.setAccessible(true);
final View view = constructor.newInstance(args);
if (view instanceof ViewStub) {
// always use ourselves when inflating ViewStub later
final ViewStub viewStub = (ViewStub) view;
viewStub.setLayoutInflater(this);
}
return view;
}
……
}