PS一句：当初你所逃避的问题终会在未来的某一天重新出现在你面前，因此，当你第一次遇到它时，请不要逃避。
相信很多初学者对XML布局怎么加载到Activity上并且显示在手机屏幕上很好奇吧？今天我们就从经常使用的方法
setContentView来从源码分析一下XML布局是怎么加载到当前Activity上的。
Activity#setContentView
我们知道，Activity是在onCreate方法中使用setContentView方法来加载布局的，那么它内部的源码是怎么实现的呢？
Setp 1
处于好奇，我们进入了Activity的源码，找到setContentView方法如下：
public void setContentView(int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}setContentView方法实现很简单，里面调用两个方法，我们这里分析第一个方法：
getWindow().setContentView(layoutResID);getWindow()得到一个Window对象 mWindow ，Window是一个抽象类，用来描述Activity视图最顶端的窗口显示和行为操作。Window是
一个抽象类，那么里面的setContentView(layoutResID)是一个抽象方法，并没有具体的实现，既然Window是一个抽象类，那么
在Activity里面就有一个Window抽象类的实现，我们查找代码发现 mWindow对象赋值方法如下：
mWindow = PolicyManager.makeNewWindow(this);Step 2
Look the fuck resoure code，继续看看 PolicyManager类
public final class More PolicyManager {
30 private static final String POLICY_IMPL_CLASS_NAME =
31 "com.android.internal.policy.impl.Policy";
32
33 private static final IPolicy sPolicy;
34
35 static {
36 // Pull in the actual implementation of the policy at run-time
37 try {
38 Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
39 sPolicy = (IPolicy)policyClass.newInstance();
40 } catch (ClassNotFoundException ex) {
41 throw new RuntimeException(
42 POLICY_IMPL_CLASS_NAME + " could not be loaded", ex);
43 } catch (InstantiationException ex) {
44 throw new RuntimeException(
45 POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
46 } catch (IllegalAccessException ex) {
47 throw new RuntimeException(
48 POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
49 }
50 }
51
52 // Cannot instantiate this class
53 private More PolicyManager() {}
54
55 // The static methods to spawn new policy-specific objects
56 public static Window More makeNewWindow(Context context) {
57 return sPolicy.makeNewWindow(context);
58 }地 57 行 sPolicy对象是有第 38，39行通过类路径”com.android.internal.policy.impl.Policy“生成的，那么我们在源码中找到 Policy类，在此类中找到了如下方法：
public Window makeNewWindow(Context context) {
return new PhoneWindow(context);
}由此可见，我们终于找到Activity类中的 mWindow对象的实现类了，就是PhoneWindow类。
Setp 3
从源码发现，PhoneWindow类就是抽象类Window的实现类。那么 setContentView方法的实现也在这个类里面了，
到PhoneWindow类发现，setContentView方法实现如下：
@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);
}
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
cb.onContentChanged();
}
}首先判断mContentParent是否为null，mContentParent是什么呢？接下来会分析，一开始条件成立，进入installDecor()方法。
Setp 4
到installDecor()方法里，实现如下：
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();
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)) {
invalidatePanelMenu(FEATURE_ACTION_BAR);
}
} else {
mTitleView = (TextView)findViewById(R.id.title);
if (mTitleView != null) {
mTitleView.setLayoutDirection(mDecor.getLayoutDirection());
if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) {
View titleContainer = findViewById(
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);
}
}
}
if (mDecor.getBackground() == null && mBackgroundFallbackResource != 0) {
mDecor.setBackgroundFallback(mBackgroundFallbackResource);
}
// Only inflate or create a new TransitionManager if the caller hasn‘t
// already set a custom one.
if (hasFeature(FEATURE_ACTIVITY_TRANSITIONS)) {
if (mTransitionManager == null) {
final int transitionRes = getWindowStyle().getResourceId(
R.styleable.Window_windowContentTransitionManager,
0);
if (transitionRes != 0) {
final TransitionInflater inflater = TransitionInflater.from(getContext());
mTransitionManager = inflater.inflateTransitionManager(transitionRes,
mContentParent);
} else {
mTransitionManager = new TransitionManager();
}
}
mEnterTransition = getTransition(mEnterTransition, null,
R.styleable.Window_windowEnterTransition);
mReturnTransition = getTransition(mReturnTransition, USE_DEFAULT_TRANSITION,
R.styleable.Window_windowReturnTransition);
mExitTransition = getTransition(mExitTransition, null,
R.styleable.Window_windowExitTransition);
mReenterTransition = getTransition(mReenterTransition, USE_DEFAULT_TRANSITION,
R.styleable.Window_windowReenterTransition);
mSharedElementEnterTransition = getTransition(mSharedElementEnterTransition, null,
R.styleable.Window_windowSharedElementEnterTransition);
mSharedElementReturnTransition = getTransition(mSharedElementReturnTransition,
USE_DEFAULT_TRANSITION,
R.styleable.Window_windowSharedElementReturnTransition);
mSharedElementExitTransition = getTransition(mSharedElementExitTransition, null,
R.styleable.Window_windowSharedElementExitTransition);
mSharedElementReenterTransition = getTransition(mSharedElementReenterTransition,
USE_DEFAULT_TRANSITION,
R.styleable.Window_windowSharedElementReenterTransition);
if (mAllowEnterTransitionOverlap == null) {
mAllowEnterTransitionOverlap = getWindowStyle().getBoolean(
R.styleable.Window_windowAllowEnterTransitionOverlap, true);
}
if (mAllowReturnTransitionOverlap == null) {
mAllowReturnTransitionOverlap = getWindowStyle().getBoolean(
R.styleable.Window_windowAllowReturnTransitionOverlap, true);
}
if (mBackgroundFadeDurationMillis < 0) {
mBackgroundFadeDurationMillis = getWindowStyle().getInteger(
R.styleable.Window_windowTransitionBackgroundFadeDuration,
DEFAULT_BACKGROUND_FADE_DURATION_MS);
}
if (mSharedElementsUseOverlay == null) {
mSharedElementsUseOverlay = getWindowStyle().getBoolean(
R.styleable.Window_windowSharedElementsUseOverlay, true);
}
}
}
}在代码的第 3 行我们看到 mDecor = generateDecor();方法调用，继续跳进 generateDecor()方法：
protected DecorView generateDecor() {
return new DecorView(getContext(), -1);
}这里生成一个DecorView对象，DecorView是PhoneWindow类的内部类，继承自FrameLayout。到目前为止，setContentView
方法里生成一个FrameLayout类型的DecorView组件。
Step 5
继续分析代码，看第 11 行：
mContentParent = generateLayout(mDecor);把 DecorView 对象 mDecor 作为参数传递给 generateLayout方法得到 mContentParent。generateLayout()方法中的代码实现如下：
protected ViewGroup generateLayout(DecorView decor) {
// Apply data from current theme.
TypedArray a = getWindowStyle();
.........
/**以下这些是Activity 窗口属性特征的设置*/
//窗口是否浮动，一般用于Dialog窗口是否浮动：是否显示在布局的正中间。
mIsFloating = a.getBoolean(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);
}
//设置窗口是否支持标题栏，隐藏显示标题栏操作在此处。
if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
requestFeature(FEATURE_NO_TITLE);
} else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
// Don‘t allow an action bar if there is no title.
requestFeature(FEATURE_ACTION_BAR);
}
//ActionBar导航栏是否不占布局空间叠加显示在当前窗口之上。
if (a.getBoolean(R.styleable.Window_windowActionBarOverlay, false)) {
requestFeature(FEATURE_ACTION_BAR_OVERLAY);
}
if (a.getBoolean(R.styleable.Window_windowActionModeOverlay, false)) {
requestFeature(FEATURE_ACTION_MODE_OVERLAY);
}
if (a.getBoolean(R.styleable.Window_windowSwipeToDismiss, false)) {
requestFeature(FEATURE_SWIPE_TO_DISMISS);
}
//当前Activity是否支持全屏
if (a.getBoolean(R.styleable.Window_windowFullscreen, false)) {
setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));
}
................
//设置状态栏的颜色
if (!mForcedStatusBarColor) {
mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000);
}
//设置导航栏的颜色
if (!mForcedNavigationBarColor) {
mNavigationBarColor = a.getColor(R.styleable.Window_navigationBarColor, 0xFF000000);
}
if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion
>= android.os.Build.VERSION_CODES.HONEYCOMB) {
if (a.getBoolean(
R.styleable.Window_windowCloseOnTouchOutside,
false)) {
setCloseOnTouchOutsideIfNotSet(true);
}
}
WindowManager.LayoutParams params = getAttributes();
//设置输入法的状态
if (!hasSoftInputMode()) {
params.softInputMode = a.getInt(
R.styleable.Window_windowSoftInputMode,
params.softInputMode);
}
if (a.getBoolean(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);
}
}
//设置当前Activity的出现动画效果
if (params.windowAnimations == 0) {
params.windowAnimations = a.getResourceId(
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(
R.styleable.Window_windowBackground, 0);
}
if (mFrameResource == 0) {
mFrameResource = a.getResourceId(R.styleable.Window_windowFrame, 0);
}
mBackgroundFallbackResource = a.getResourceId(
R.styleable.Window_windowBackgroundFallback, 0);
if (false) {
System.out.println("Background: "
+ Integer.toHexString(mBackgroundResource) + " Frame: "
+ Integer.toHexString(mFrameResource));
}
}
mElevation = a.getDimension(R.styleable.Window_windowElevation, 0);
mClipToOutline = a.getBoolean(R.styleable.Window_windowClipToOutline, false);
mTextColor = a.getColor(R.styleable.Window_textColor, Color.TRANSPARENT);
}
//以下代码为当前Activity窗口添加 decor根布局。
// 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();
//通过布局添加器LayoutInflater获取layoutResource布局，
View in = mLayoutInflater.inflate(layoutResource, null);
//将XML资源为layoutResource的布局添加到decor容器里面，至此PhoneWindow 内部类DecorView就添加了之布局
decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
mContentRoot = (ViewGroup) in;
//此处很重要，通过findViewById找到 contentParent容器，也是该方法的返回值。
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.
//以下代码设置Activity窗口的背景，标题等
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;
}以上代码代比较复杂，主要做了以下几件事情。
- 从第 8 行到第110行，主要是初始化窗口的特征，是否显示标题栏，是否全屏，是否支持ActionBar浮动等等。
- 第112-187行，主要是给容器DecorView添加id为layoutResource布局的根布局。待会分析layoutResource布局。
- 第178行，通过LayoutInflater 将xml布局转换成VIEW.
- 第180行将找到的View添加到DecorView根布局当中。
- 第184行，从根布局中找到id为R.id.content的 contentParent 容器。也就是当前方法的返回值。
接下来，看看 id为layoutResource的布局到底实现了什么？我们来看看171行的R.layout.screen_simple;资源
<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>
原来我们的DecorView根布局里面添加了类似上面的布局，线性布局LinearLaout里包含两个组件，ViewStub是懒加载，默认不显示，FrameLayout是什么呢？看看id=content，就是我们184行找到的父容器 contentParent。那么这个父容器 contentParent有什么作用呢？
我们回到 Step4 的第 11行，mContentParent = generateLayout(mDecor); 获得 父容器 mContentParent。我们再次回到 Step3步的第17行， mLayoutInflater.inflate(layoutResID, mContentParent); 这里通过LayoutInflater将 setContentView（layoutResID）传进来的布局id加载到 父容器mContentParent中，至此，setContentView就将布局添加到Activity里面了。
现在我们来梳理一下流程：
Activity setContentView—>Window setContentView—>PhoneWindow setContentView—->PhoneWindow installDecor—–>PhoneWindow generateLayout——>PhoneWindow mLayoutInflater.inflate(layoutResID, mContentParent);
Activity 类中有一个Window抽象类的实现PhoneWindow类，该类中有个内部类DecorView，继承自FrameLayout，在DecorView容器中添加了根布局，根布局中包含了一个id为 contnet的FrameLayout 内容布局，我们的Activity加载的布局xml最后添加到 id为content的FrameLayout布局当中了。用一个图来描述，如下：
总结：
1.关于requestWindowFeature(Window.FEATURE_NO_TITLE); 去除标题栏的疑问，如果你自己的xxxActivity是继承自Activity，那么恭喜你使用以上方法可以去除标题栏，如果你自己的xxxActivity是继承自AppCompatActivity或者ActionBarActivity，那么很遗憾告诉你，此次系统默认的标题栏已经在主题中去除，此时显示的标题栏是ActionBar导航栏，如果需要去除导航栏，你可以通过如下代码：getSupportActionBar().hide();来隐藏导航栏。
2.requestWindowFeature(Window.FEATURE_NO_TITLE);方法需要在 setContentView方法之前使用，由上面 Step5分析可得，设置Activity Window 特征是在setContentView方法中设置的，因此，如果需要改变Activity Window窗口特征，需要在setContentView方法之前。其实这里有疑问？？？为什么设置全屏的方法
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);可以在setContentView之后呢？？？求解。
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时间： 2024-10-19 19:20:01