先來看Activity代碼
public void setContentView(@LayoutRes int layoutResID) {
//window是一個抽象類，PhoneWindow是它的唯一實現類
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
看getWindow
public Window getWindow() {
return mWindow;
}
//其中PhoneWindow是它的唯一實現類
mWindow = new PhoneWindow(this, window, activityConfigCallback);
看PhoneWindow
@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) {
//第一次進來走這里，建立DecorView并初始化其布局
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);
}
mContentParent.requestApplyInsets();
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
cb.onContentChanged();
}
mContentParentExplicitlySet = true;
}
繼續
private void installDecor() {
mForceDecorInstall = false;
if (mDecor == null) {
//generateDecor的作用是new DecorView()
mDecor = generateDecor(-1);
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
} else {
mDecor.setWindow(this);
}
if (mContentParent == null) {
//初始化 DecorView 的布局
mContentParent = generateLayout(mDecor);
protected DecorView generateDecor(int featureId) {
// System process doesn't have application context and in that case we need to directly use
// the context we have. Otherwise we want the application context, so we don't cling to the
// activity.
Context context;
if (mUseDecorContext) {
Context applicationContext = getContext().getApplicationContext();
if (applicationContext == null) {
context = getContext();
} else {
context = new DecorContext(applicationContext, getContext());
if (mTheme != -1) {
context.setTheme(mTheme);
}
}
} else {
context = getContext();
}
//重點
return new DecorView(context, featureId, this, getAttributes());
}
//DecorView是FrameLayout
public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;
protected ViewGroup generateLayout(DecorView 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;
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 {
// Embedded, so no decoration is needed.
layoutResource = R.layout.screen_simple;
// System.out.println("Simple!");
}
mDecor.startChanging();
mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
}
從上面的源碼可以看出實際上 DecorView 里面包含了一個系統內置的布局資源，這個布局資源 layoutResource 會根據不同主題變化，其中一個資源是 com.android.internal.R.layout.screen_simple，該資源文件里有一個 ID 為 content 的 FrameLayout，它就是我們前面看到的 mContentParent，我們設置的布局文件就是被解析并添加到 mContentParent 中的：
這是R.layout.screen_simple布局
<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" />
<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>
再來看AppCompatActivity
public void setContentView(@LayoutRes int layoutResID) {
this.getDelegate().setContentView(layoutResID);
}
看getDelegate方法
@NonNull
public AppCompatDelegate getDelegate() {
if (this.mDelegate == null) {
this.mDelegate = AppCompatDelegate.create(this, this);
}
return this.mDelegate;
}
public static AppCompatDelegate create(Activity activity, AppCompatCallback callback) {
return new AppCompatDelegateImpl(activity, activity.getWindow(), callback);
}
再來看AppCompatDelegateImpl
class AppCompatDelegateImpl extends AppCompatDelegate implements Callback, Factory2 {
public void setContentView(int resId) {
this.ensureSubDecor();
ViewGroup contentParent = (ViewGroup)this.mSubDecor.findViewById(16908290);
contentParent.removeAllViews();
//解析xml,跟蹤inflate方法，最終找到下面兩個方法
LayoutInflater.from(this.mContext).inflate(resId, contentParent);
this.mOriginalWindowCallback.onContentChanged();
}
//初始化所有view的工廠，該方法在AppCompatActivity的onCreate方法中調用，
public void installViewFactory() {
LayoutInflater layoutInflater = LayoutInflater.from(this.mContext);
if (layoutInflater.getFactory() == null) {
LayoutInflaterCompat.setFactory2(layoutInflater, this);
} else if (!(layoutInflater.getFactory2() instanceof AppCompatDelegateImpl)) {
Log.i("AppCompatDelegate", "The Activity's LayoutInflater already has a Factory installed so we can not install AppCompat's");
}
}
//這個方法是通過追蹤inflate方法找到的
public View createView(View parent, String name, @NonNull Context context, @NonNull AttributeSet attrs) {
if (this.mAppCompatViewInflater == null) {
TypedArray a = this.mContext.obtainStyledAttributes(styleable.AppCompatTheme);
String viewInflaterClassName = a.getString(styleable.AppCompatTheme_viewInflaterClass);
if (viewInflaterClassName != null && !AppCompatViewInflater.class.getName().equals(viewInflaterClassName)) {
try {
Class viewInflaterClass = Class.forName(viewInflaterClassName);
this.mAppCompatViewInflater = (AppCompatViewInflater)viewInflaterClass.getDeclaredConstructor().newInstance();
} catch (Throwable var8) {
Log.i("AppCompatDelegate", "Failed to instantiate custom view inflater " + viewInflaterClassName + ". Falling back to default.", var8);
this.mAppCompatViewInflater = new AppCompatViewInflater();
}
} else {
this.mAppCompatViewInflater = new AppCompatViewInflater();
}
}
boolean inheritContext = false;
if (IS_PRE_LOLLIPOP) {
inheritContext = attrs instanceof XmlPullParser ? ((XmlPullParser)attrs).getDepth() > 1 : this.shouldInheritContext((ViewParent)parent);
}
return this.mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext, IS_PRE_LOLLIPOP, true, VectorEnabledTintResources.shouldBeUsed());
}
追蹤inflate
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
return inflate(resource, root, root != null);
}
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
final Resources res = getContext().getResources();
if (DEBUG) {
Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" ("
+ Integer.toHexString(resource) + ")");
}
final XmlResourceParser parser = res.getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}
public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");
final Context inflaterContext = mContext;
final AttributeSet attrs = Xml.asAttributeSet(parser);
Context lastContext = (Context) mConstructorArgs[0];
mConstructorArgs[0] = inflaterContext;
View result = root;
try {
// Look for the root node.
int type;
while ((type = parser.next()) != XmlPullParser.START_TAG &&
type != XmlPullParser.END_DOCUMENT) {
// Empty
}
if (type != XmlPullParser.START_TAG) {
throw new InflateException(parser.getPositionDescription()
+ ": No start tag found!");
}
final String name = parser.getName();
if (DEBUG) {
System.out.println("**************************");
System.out.println("Creating root view: "
+ name);
System.out.println("**************************");
}
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, inflaterContext, attrs, false);
} else {
// Temp is the root view that was found in the xml
//看這個創建view的方法
final View temp = createViewFromTag(root, name, inflaterContext, 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");
}
// Inflate all children under temp against its context.
rInflateChildren(parser, temp, attrs, true);
if (DEBUG) {
System.out.println("-----> done inflating children");
}
// We are supposed to attach all the views we found (int temp)
// to root. Do that now.
if (root != null && attachToRoot) {
root.addView(temp, params);
}
// Decide whether to return the root that was passed in or the
// top view found in xml.
if (root == null || !attachToRoot) {
result = temp;
}
}
} catch (XmlPullParserException e) {
final InflateException ie = new InflateException(e.getMessage(), e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
} catch (Exception e) {
final InflateException ie = new InflateException(parser.getPositionDescription()
+ ": " + e.getMessage(), e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
} finally {
// Don't retain static reference on context.
mConstructorArgs[0] = lastContext;
mConstructorArgs[1] = null;
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
return result;
}
}
private View createViewFromTag(View parent, String name, Context context, AttributeSet attrs) {
return createViewFromTag(parent, name, context, attrs, false);
}
View createViewFromTag(View parent, String name, Context context, AttributeSet attrs,
boolean ignoreThemeAttr) {
if (name.equals("view")) {
name = attrs.getAttributeValue(null, "class");
}
// Apply a theme wrapper, if allowed and one is specified.
if (!ignoreThemeAttr) {
final TypedArray ta = context.obtainStyledAttributes(attrs, ATTRS_THEME);
final int themeResId = ta.getResourceId(0, 0);
if (themeResId != 0) {
context = new ContextThemeWrapper(context, themeResId);
}
ta.recycle();
}
if (name.equals(TAG_1995)) {
// Let's party like it's 1995!
return new BlinkLayout(context, attrs);
}
try {
View view;
//AppCompatActivity中設置了mFactory2，Factory2是一個接口，AppCompatDelegateImpl實現了該接口，從而找到了AppCompatDelegateImpl中的onCreateView方法
if (mFactory2 != null) {
view = mFactory2.onCreateView(parent, name, context, attrs);
} else if (mFactory != null) {
view = mFactory.onCreateView(name, context, attrs);
} else {
view = null;
}
if (view == null && mPrivateFactory != null) {
view = mPrivateFactory.onCreateView(parent, name, context, attrs);
}
if (view == null) {
final Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = context;
try {
//重點，如果是系統控件，則會在name前面加上"android.view."
if (-1 == name.indexOf('.')) {
view = onCreateView(parent, name, attrs);
} else {
//并且從createView方法可以看出，系統是通過反射創建view的
view = createView(name, null, attrs);
}
} finally {
mConstructorArgs[0] = lastContext;
}
}
return view;
} catch (InflateException e) {
throw e;
} catch (ClassNotFoundException e) {
final InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class " + name, e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
} catch (Exception e) {
final InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class " + name, e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
}
}
系統是通過反射創建view的？從 LayoutInflater 的源碼看下去, 能夠看到 View 實例化的過程createView
public final View createView(String name, String prefix, AttributeSet attrs)
throws ClassNotFoundException, InflateException {
Constructor<? extends View> constructor = sConstructorMap.get(name);
if (constructor != null && !verifyClassLoader(constructor)) {
constructor = null;
sConstructorMap.remove(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);
constructor.setAccessible(true);
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 lastContext = mConstructorArgs[0];
if (mConstructorArgs[0] == null) {
// Fill in the context if not already within inflation.
mConstructorArgs[0] = mContext;
}
Object[] args = mConstructorArgs;
args[1] = attrs;
//最后根據Constructor實例化view對象
final View view = constructor.newInstance(args);
if (view instanceof ViewStub) {
// Use the same context when inflating ViewStub later.
final ViewStub viewStub = (ViewStub) view;
viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
}
mConstructorArgs[0] = lastContext;
return view;
} catch (NoSuchMethodException e) {
final InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Error inflating class " + (prefix != null ? (prefix + name) : name), e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
} catch (ClassCastException e) {
// If loaded class is not a View subclass
final InflateException ie = new InflateException(attrs.getPositionDescription()
+ ": Class is not a View " + (prefix != null ? (prefix + name) : name), e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
} catch (ClassNotFoundException e) {
// If loadClass fails, we should propagate the exception.
throw e;
} catch (Exception e) {
final InflateException ie = new InflateException(
attrs.getPositionDescription() + ": Error inflating class "
+ (clazz == null ? "<unknown>" : clazz.getName()), e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
回到AppCompatDelegateImpl的createView方法，其調用了AppCompatViewInflater的createView方法
final View createView(View parent, String name, @NonNull Context context, @NonNull AttributeSet attrs, boolean inheritContext, boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {
Context originalContext = context;
if (inheritContext && parent != null) {
context = parent.getContext();
}
if (readAndroidTheme || readAppTheme) {
context = themifyContext(context, attrs, readAndroidTheme, readAppTheme);
}
if (wrapContext) {
context = TintContextWrapper.wrap(context);
}
View view = null;
byte var12 = -1;
switch(name.hashCode()) {
case -1946472170:
if (name.equals("RatingBar")) {
var12 = 11;
}
break;
case -1455429095:
if (name.equals("CheckedTextView")) {
var12 = 8;
}
break;
case -1346021293:
if (name.equals("MultiAutoCompleteTextView")) {
var12 = 10;
}
break;
case -938935918:
if (name.equals("TextView")) {
var12 = 0;
}
break;
case -937446323:
if (name.equals("ImageButton")) {
var12 = 5;
}
break;
case -658531749:
if (name.equals("SeekBar")) {
var12 = 12;
}
break;
case -339785223:
if (name.equals("Spinner")) {
var12 = 4;
}
break;
case 776382189:
if (name.equals("RadioButton")) {
var12 = 7;
}
break;
case 1125864064:
if (name.equals("ImageView")) {
var12 = 1;
}
break;
case 1413872058:
if (name.equals("AutoCompleteTextView")) {
var12 = 9;
}
break;
case 1601505219:
if (name.equals("CheckBox")) {
var12 = 6;
}
break;
case 1666676343:
if (name.equals("EditText")) {
var12 = 3;
}
break;
case 2001146706:
if (name.equals("Button")) {
var12 = 2;
}
}
switch(var12) {
case 0:
view = this.createTextView(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 1:
view = this.createImageView(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 2:
view = this.createButton(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 3:
view = this.createEditText(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 4:
view = this.createSpinner(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 5:
view = this.createImageButton(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 6:
view = this.createCheckBox(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 7:
view = this.createRadioButton(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 8:
view = this.createCheckedTextView(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 9:
view = this.createAutoCompleteTextView(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 10:
view = this.createMultiAutoCompleteTextView(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 11:
view = this.createRatingBar(context, attrs);
this.verifyNotNull((View)view, name);
break;
case 12:
view = this.createSeekBar(context, attrs);
this.verifyNotNull((View)view, name);
break;
default:
view = this.createView(context, name, attrs);
}
if (view == null && originalContext != context) {
view = this.createViewFromTag(context, name, attrs);
}
if (view != null) {
this.checkOnClickListener((View)view, attrs);
}
return (View)view;
}
@NonNull
protected AppCompatTextView createTextView(Context context, AttributeSet attrs) {
return new AppCompatTextView(context, attrs);
}
@NonNull
protected AppCompatImageView createImageView(Context context, AttributeSet attrs) {
return new AppCompatImageView(context, attrs);
}
widget 的layout 在inflation 的時候，被AppCompatDelegate 攔截下來，不會走系統的LayoutInflater的創建，然后根據控件的名字，強制被系統轉換成為 以AppCompat 開頭的控件,兼容控件繼承原控件，在使用過程中，開發人員寫法和原來一樣。
再來看LayoutInflater
View view = View.inflate(this, R.layout.activity_handler, null);
//第一個方法調用第二個方法
view = LayoutInflater.from(this).inflate(R.layout.activity_handler,null);
//第二個方法調用第三個方法，我們從這看源碼
view = LayoutInflater.from(this).inflate(R.layout.activity_handler,null,false);
下片文章我們分析一下inflate這三個方法的參數和使用過程中出現的問題LayoutInflater中inflate方法三個參數的區別
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;
}
在ContextImpl中看getSystemService
@Override
public Object getSystemService(String name) {
return SystemServiceRegistry.getSystemService(this, name);
}
public static Object getSystemService(ContextImpl ctx, String name) {
ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
return fetcher != null ? fetcher.getService(ctx) : null;
}
//static 的map實現單例
private static final HashMap<String, ServiceFetcher<?>> SYSTEM_SERVICE_FETCHERS =
new HashMap<String, ServiceFetcher<?>>();
LayoutInflater.from(this)是一個系統服務，單例模式
