我们日常在开发中在Activity设置布局的时候都会用到setContentView方法，那setContentView到底是如何实现添加布局的呢，带着这个疑问本篇文章来详细查看源码分析setContentView加载布局的流程，首先我们先看Activity的setContentView方法
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
在这里 getWindow()获取的是mWindow这个变量就是Window，mWindow实例化就是PhoneWindow
mWindow = new PhoneWindow(this, window, activityConfigCallback);
mWindow.setWindowControllerCallback(this);
mWindow.setCallback(this);
mWindow.setOnWindowDismissedCallback(this);
我们查看PhoneWindow中的setContentView方法
@Override
public void setContentView(int layoutResID) {
if (mContentParent == null) {
第一次会走进这里
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 {
最终获取的mContentParent加载显示布局
mLayoutInflater.inflate(layoutResID, mContentParent);
}
mContentParent.requestApplyInsets();
.....省略
我们看下mContentParent到底是怎么实例化的，进入installDecor方法
mForceDecorInstall = false;
if (mDecor == null) {
创建一个DecorView
mDecor = generateDecor(-1);
...
} else {
mDecor.setWindow(this);
}
if (mContentParent == null) {
创建mContentParent
mContentParent = generateLayout(mDecor);
...设置一些属性
}
所以从这里可以看出Activity的布局加载是先创建一个PhoneWindow的窗口布局，然后在PhoneWindow内又创建一个窗口布局DecorView就是个FrameLayout，嵌套了两层，我们再看generateLayout方法
...获取一些属性
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;
setCloseOnSwipeEnabled(true);
} 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 {
获取系统布局
layoutResource = R.layout.screen_simple;
// System.out.println("Simple!");
}
mDecor.startChanging();
获取到layoutResource，填充DecorView
mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
找一个叫做android.id.content的FrameLayout系统布局
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
if (contentParent == null) {
throw new RuntimeException("Window couldn't find content container view");
}
....
找到返回
return contentParent;
这个方法主要是加载系统一些资源做了一系列的判断，先获取到layoutResource去填充DecorView，然后获取系统布局中的FrameLayout的id，这个id就是从screen_simple布局中获取的
void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
if (mBackdropFrameRenderer != null) {
loadBackgroundDrawablesIfNeeded();
mBackdropFrameRenderer.onResourcesLoaded(
this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,
mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),
getCurrentColor(mNavigationColorViewState));
}
mDecorCaptionView = createDecorCaptionView(inflater);
获取到root
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 {
系统布局添加到DecorView中
addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
mContentRoot = (ViewGroup) root;
initializeElevation();
}
public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;
<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>
从源码可以看出DecorView又添加了一个系统的布局，所以现在已经嵌套第三层了，但是在系统布局中还有个FrameLayout，这样就嵌套了四层，也就是说最终加载我们自己的布局也就是加到系统布局中的FrameLayout，如果有头部布局就会加载系统的头部布局，没有则不加。下面画的一张图加以说明：
布局加载流程.png
接下来我们再来看下AppCompateActivity的setContentView源码
@Override
public void setContentView(@LayoutRes int layoutResID) {
initViewTreeOwners();
getDelegate().setContentView(layoutResID);
}
public abstract void setContentView(@LayoutRes int resId);
@NonNull
public AppCompatDelegate getDelegate() {
if (mDelegate == null) {
mDelegate = AppCompatDelegate.create(this, this);
}
return mDelegate;
}
跟进去看下发现是一个抽象方法，抽象方法一定会有实现类，我们找到它的实现类，点击进入AppCompatDelegate.create方法，找到对应的实现类
@NonNull
public static AppCompatDelegate create(@NonNull Activity activity,
@Nullable AppCompatCallback callback) {
return new AppCompatDelegateImpl(activity, callback);
}
我们进入AppCompatDelegateImpl中找到setContentView方法看看具体怎么实现的
@Override
public void setContentView(View v) {
ensureSubDecor();
ViewGroup contentParent = mSubDecor.findViewById(android.R.id.content);
contentParent.removeAllViews();
写好的布局添加到contentParent中
contentParent.addView(v);
mAppCompatWindowCallback.getWrapped().onContentChanged();
}
发现和Activity的写法类似也是获取android.R.id.content，我们进入ensureSubDecor方法看看到底怎么处理的
private void ensureSubDecor() {
if (!mSubDecorInstalled) {
获取到mSubDecor 是一个ViewGroup
mSubDecor = createSubDecor();
CharSequence title = getTitle();
if (!TextUtils.isEmpty(title)) {
if (mDecorContentParent != null) {
mDecorContentParent.setWindowTitle(title);
} else if (peekSupportActionBar() != null) {
peekSupportActionBar().setWindowTitle(title);
} else if (mTitleView != null) {
mTitleView.setText(title);
}
}
applyFixedSizeWindow();
onSubDecorInstalled(mSubDecor);
mSubDecorInstalled = true;
onCreateOptionsMenu
PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
if (!mDestroyed && (st == null || st.menu == null)) {
invalidatePanelMenu(FEATURE_SUPPORT_ACTION_BAR);
}
}
}
看看mSubDecor 是怎样创建的，进入createSubDecor方法
private ViewGroup createSubDecor() {
....设置一些属性
这个方法是获取PhoneWindow
ensureWindow();
这是获取PhoneWindow内创建的DecorView
mWindow.getDecorView();
final LayoutInflater inflater = LayoutInflater.from(mContext);
ViewGroup subDecor = null;
if (!mWindowNoTitle) {
if (mIsFloating) {
// If we're floating, inflate the dialog title decor
subDecor = (ViewGroup) inflater.inflate(
R.layout.abc_dialog_title_material, null);
// Floating windows can never have an action bar, reset the flags
mHasActionBar = mOverlayActionBar = false;
} else if (mHasActionBar) {
/**
* This needs some explanation. As we can not use the android:theme attribute
* pre-L, we emulate it by manually creating a LayoutInflater using a
* ContextThemeWrapper pointing to actionBarTheme.
*/
TypedValue outValue = new TypedValue();
mContext.getTheme().resolveAttribute(R.attr.actionBarTheme, outValue, true);
Context themedContext;
if (outValue.resourceId != 0) {
themedContext = new ContextThemeWrapper(mContext, outValue.resourceId);
} else {
themedContext = mContext;
}
// Now inflate the view using the themed context and set it as the content view
subDecor = (ViewGroup) LayoutInflater.from(themedContext)
.inflate(R.layout.abc_screen_toolbar, null);
mDecorContentParent = (DecorContentParent) subDecor
.findViewById(R.id.decor_content_parent);
mDecorContentParent.setWindowCallback(getWindowCallback());
/**
* Propagate features to DecorContentParent
*/
if (mOverlayActionBar) {
mDecorContentParent.initFeature(FEATURE_SUPPORT_ACTION_BAR_OVERLAY);
}
if (mFeatureProgress) {
mDecorContentParent.initFeature(Window.FEATURE_PROGRESS);
}
if (mFeatureIndeterminateProgress) {
mDecorContentParent.initFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
}
}
} else {
if (mOverlayActionMode) {
默认会走到这里
subDecor = (ViewGroup) inflater.inflate(
R.layout.abc_screen_simple_overlay_action_mode, null);
} else {
subDecor = (ViewGroup) inflater.inflate(R.layout.abc_screen_simple, null);
}
}
if (subDecor == null) {
throw new IllegalArgumentException(
"AppCompat does not support the current theme features: { "
+ "windowActionBar: " + mHasActionBar
+ ", windowActionBarOverlay: "+ mOverlayActionBar
+ ", android:windowIsFloating: " + mIsFloating
+ ", windowActionModeOverlay: " + mOverlayActionMode
+ ", windowNoTitle: " + mWindowNoTitle
+ " }");
}
.... 一些兼容的判断
if (mDecorContentParent == null) {
mTitleView = (TextView) subDecor.findViewById(R.id.title);
}
// Make the decor optionally fit system windows, like the window's decor
ViewUtils.makeOptionalFitsSystemWindows(subDecor);
获取系统布局中的ContentFrameLayout
final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
R.id.action_bar_activity_content);
获取PhoneWindow中的系统布局FrameLayout
final ViewGroup windowContentView = (ViewGroup) mWindow.findViewById(android.R.id.content);
if (windowContentView != null) {
如果有子布局
while (windowContentView.getChildCount() > 0) {
获取PhoneWindow中的子布局
final View child = windowContentView.getChildAt(0);
删除PhoneWindow中的根布局
windowContentView.removeViewAt(0);
子布局重新添加到contentView中
contentView.addView(child);
}
// Change our content FrameLayout to use the android.R.id.content id.
清除PhoneWindow的id
windowContentView.setId(View.NO_ID);
重新设置id
contentView.setId(android.R.id.content);
// The decorContent may have a foreground drawable set (windowContentOverlay).
// Remove this as we handle it ourselves
if (windowContentView instanceof FrameLayout) {
((FrameLayout) windowContentView).setForeground(null);
}
}
重新添加到DecorView
mWindow.setContentView(subDecor);
contentView.setAttachListener(new ContentFrameLayout.OnAttachListener() {
@Override
public void onAttachedFromWindow() {}
@Override
public void onDetachedFromWindow() {
dismissPopups();
}
});
返回重新设置的一个id为android.R.id.content的ViewGroup
return subDecor;
}
从这个方法可以看出跟Activity中的原理逻辑是一样的，只不过处理方式不太一样，我们先来看下PhoneWindow是怎样获取的，进入ensureWindow方法
private void ensureWindow() {
if (mWindow == null && mHost instanceof Activity) {
这个就很明了了其实就是获取到Activity中的实例化的PhoneWindow对象
attachToWindow(((Activity) mHost).getWindow());
}
if (mWindow == null) {
throw new IllegalStateException("We have not been given a Window");
}
}
接下来我们看看subDecor是怎样处理的，我们先看布局文件到底是咋搞的，查看abc_screen_simple_overlay_action_mode布局
<androidx.appcompat.widget.FitWindowsFrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/action_bar_root"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true">
<include layout="@layout/abc_screen_content_include" />
<androidx.appcompat.widget.ViewStubCompat
android:id="@+id/action_mode_bar_stub"
android:inflatedId="@+id/action_mode_bar"
android:layout="@layout/abc_action_mode_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</androidx.appcompat.widget.FitWindowsFrameLayout>
<merge xmlns:android="http://schemas.android.com/apk/res/android">
<androidx.appcompat.widget.ContentFrameLayout
android:id="@id/action_bar_activity_content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:foregroundGravity="fill_horizontal|top"
android:foreground="?android:attr/windowContentOverlay" />
</merge>
这个地方有点饶，我们详细看下源码发现id为action_bar_activity_content是一个ContentFrameLayout，所以根据源码可以看出来在下面获取的第一步contentView是ContentFrameLayout，然后第二步mWindow获取的android.R.id.content是PhoneWindow中的系统布局id，第三步先判断有没有子布局，如果有的话则删除自己的跟布局和id，替换成ContentFrameLayout根布局设置id为android.R.id.content，第四步修改好的subDecor布局添加到DecorView中，最后setContentView中我们自己设置的布局添加到android.R.id.content中
源码分析完了，现在我们再看Activity和AppCompateActivity的区别在哪里
通过AppCompateActivity的源码分析，我们在AppCompatDelegateImpl中发现实现了LayoutInflater.Factory2接口
public interface Factory2 extends Factory {
@Nullable
View onCreateView(@Nullable View parent, @NonNull String name,
@NonNull Context context, @NonNull AttributeSet attrs);
}
既然实现接口一定会有事件，果然发现在AppCompatDelegateImpl的事件处理，LayoutInflater源码分析本篇文章就不写了，可自行查看，这里直接讲一些，后续文章中会有补充。接者往下看
@Override
public void installViewFactory() {
LayoutInflater layoutInflater = LayoutInflater.from(mContext);
if (layoutInflater.getFactory() == null) {
设置一个Factory事件
LayoutInflaterCompat.setFactory2(layoutInflater, this);
} else {
if (!(layoutInflater.getFactory2() instanceof AppCompatDelegateImpl)) {
Log.i(TAG, "The Activity's LayoutInflater already has a Factory installed"
+ " so we can not install AppCompat's");
}
}
}
有个Factory对象就一定会走onCreateView方法，我们查看LayoutInflater中的具体实现方法
private static class FactoryMerger implements Factory2 {
private final Factory mF1, mF2;
private final Factory2 mF12, mF22;
FactoryMerger(Factory f1, Factory2 f12, Factory f2, Factory2 f22) {
mF1 = f1;
mF2 = f2;
mF12 = f12;
mF22 = f22;
}
@Nullable
public View onCreateView(@NonNull String name, @NonNull Context context,
@NonNull AttributeSet attrs) {
View v = mF1.onCreateView(name, context, attrs);
if (v != null) return v;
return mF2.onCreateView(name, context, attrs);
}
@Nullable
public View onCreateView(@Nullable View parent, @NonNull String name,
@NonNull Context context, @NonNull AttributeSet attrs) {
View v = mF12 != null ? mF12.onCreateView(parent, name, context, attrs)
: mF1.onCreateView(name, context, attrs);
if (v != null) return v;
return mF22 != null ? mF22.onCreateView(parent, name, context, attrs)
: mF2.onCreateView(name, context, attrs);
}
}
所以我们现在来查看AppCompatDelegateImpl中实现的onCreateView方法到底干了啥
@Override
public final View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
return createView(parent, name, context, attrs);
}
@Override
public View createView(View parent, final String name, @NonNull Context context,
@NonNull AttributeSet attrs) {
关注此方法
return mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext,
IS_PRE_LOLLIPOP, );
}
进入AppCompatViewInflater中的createView方法
final View createView(View parent, final String name, @NonNull Context context,
@NonNull AttributeSet attrs, boolean inheritContext,
boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {
final Context originalContext = context;
...省略
View view = null;
如果是TextView，则转换成AppCompatTextView，以此类推
switch (name) {
case "TextView":
view = createTextView(context, attrs);
verifyNotNull(view, name);
break;
case "ImageView":
view = createImageView(context, attrs);
verifyNotNull(view, name);
break;
case "Button":
view = createButton(context, attrs);
verifyNotNull(view, name);
break;
case "EditText":
view = createEditText(context, attrs);
verifyNotNull(view, name);
break;
case "Spinner":
view = createSpinner(context, attrs);
verifyNotNull(view, name);
break;
case "ImageButton":
view = createImageButton(context, attrs);
verifyNotNull(view, name);
break;
case "CheckBox":
view = createCheckBox(context, attrs);
verifyNotNull(view, name);
break;
case "RadioButton":
view = createRadioButton(context, attrs);
verifyNotNull(view, name);
break;
case "CheckedTextView":
view = createCheckedTextView(context, attrs);
verifyNotNull(view, name);
break;
case "AutoCompleteTextView":
view = createAutoCompleteTextView(context, attrs);
verifyNotNull(view, name);
break;
case "MultiAutoCompleteTextView":
view = createMultiAutoCompleteTextView(context, attrs);
verifyNotNull(view, name);
break;
case "RatingBar":
view = createRatingBar(context, attrs);
verifyNotNull(view, name);
break;
case "SeekBar":
view = createSeekBar(context, attrs);
verifyNotNull(view, name);
break;
case "ToggleButton":
view = createToggleButton(context, attrs);
verifyNotNull(view, name);
break;
default:
view = createView(context, name, attrs);
}
......省略
if (view == null && originalContext != context) {
这个方法是自定义控件，构造方法通过反射进行创建的
view = createViewFromTag(context, name, attrs);
}
return view;
}
@NonNull
protected AppCompatTextView createTextView(Context context, AttributeSet attrs) {
return new AppCompatTextView(context, attrs);
}
从这里我们就看清楚了，其实它就是把我们在布局中设置的控件转换成带有 AppCompat兼容控件
最后总结一下：AppCompateActivity创建View的时候会被拦截，不会走系统的LayoutInflater的创建，就会替换一些系统兼容的View
