Android源码分析-setContentView加载布局流程
上篇文章追溯了Android源码中Activity的启动流程，那么Activity启动以后，是如何加载布局的呢？这篇文章咱们继续来追溯这一块的Android源码。node
Activity->setContentView
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
复制代码
这里调用了Window的setContentView方法，而Window是一个抽象类，PhoneWindow是其惟一派生子类，因此这里调用的是PhoneWindow中的setContentView方法。android
PhoneWindow->setContentView
@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) {////////////////////////////////////////////////// TAG1
//建立DecorView，并添加到mContentParent上
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 {
//将布局加载到mContentParent上
mLayoutInflater.inflate(layoutResID, mContentParent);/////////////////////// TAG2
}
mContentParent.requestApplyInsets();
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
//回调通知界面加载完毕
cb.onContentChanged();
}
mContentParentExplicitlySet = true;
}
复制代码
首先看标识TAG1处，这里判断mContentParent是否为空，后面咱们能够知道这个mContentParent表示的是DecorView中展现内容的布局（除去标题栏）。到这一步，咱们尚未建立过DecorView，也就更不可能生成mContentParent了，因此这里的判断是为true的。也就是会执行installDecor()方法。windows
Activity->installDecor
private void installDecor() {
mForceDecorInstall = false;
///////////////////////////////////////////////////////////////////////// TAG3
if (mDecor == null) {
//若是mDecor为空，建立一个DecorView赋给mDecor
mDecor = generateDecor(-1);
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
} else {
mDecor.setWindow(this);
}
///////////////////////////////////////////////////////////////////////// TAG4
if (mContentParent == null) {
//根据主题以及设置的FEATURE为mDecor添加默认布局
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);
//添加其余资源
......
//设置转场动画
if (hasFeature(FEATURE_ACTIVITY_TRANSITIONS)) {
......
}
}
}
复制代码
TAG3处没什么好说的，就是建立一个DecorView赋给mDecor。 这里咱们重点看TAG4处新建mContentParent的过程，调用的是generateLayout(mDecor)方法。缓存
PhoneWindow->generateLayout(DecorView decor)
protected ViewGroup generateLayout(DecorView decor) {
// Apply data from current theme.
//获取当前设置的窗口主题
//这也就是为何咱们要在setContentView以前调用requesetFeature的缘由
TypedArray a = getWindowStyle();
......//根据设置加载默认主题
// Inflate the window decor.
int layoutResource;
int features = getLocalFeatures();
// System.out.println("Features: 0x" + Integer.toHexString(features));
// 根据用户设置的Feature来设置DecorView的布局资源
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 ......一系列的判断
mDecor.startChanging();
//将符合配置的布局建立并添加到DecorView中
mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
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);
}
}
//右划退出
if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
registerSwipeCallbacks(contentParent);
}
// Remaining setup -- of background and title -- that only applies
// to top-level windows.
// 设置背景和标题
if (getContainer() == null) {
......
}
mDecor.finishChanging();
return contentParent;
}
复制代码
方法里先是获取了咱们设置的窗口主题，并加载相应的主题。而后又根据咱们设置的Feature来选择相应的布局资源，最后调用mDecor.onResourcesLoaded(mLayoutInflater, layoutResource)方法将布局实例化并添加到DecorView上。bash
DecorView->onResourcesLoaded
void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
if (mBackdropFrameRenderer != null) {
loadBackgroundDrawablesIfNeeded();
mBackdropFrameRenderer.onResourcesLoaded(
this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,
mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),
getCurrentColor(mNavigationColorViewState));
}
mDecorCaptionView = createDecorCaptionView(inflater);
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 {
// Put it below the color views.
addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
mContentRoot = (ViewGroup) root;
initializeElevation();
}
复制代码
这里经过inflater.inflate方法将布局建立出来，而后经过addView将布局添加到DecorView上，关于inflate的源码后面会进行分析。 到这里，TAG1处的installDecor方法流程就走完了。它建立了Activity的DecorView，设置了DecorView的主题以及布局。 如今，回到PhoneWindow的setContentView方法，看TAG2处的代码。这里调用了mLayoutInflater.inflate(layoutResID, mContentParent)方法，将咱们设置的布局加载到mContentParent上。app
LayoutInflater->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();
}
}
复制代码
这里经过res.getLayout(resource)方法对布局资源进行了XML解析，将布局资源解析成XmlResourceParser对象，而后调用同名的inflate方法进行下一步操做。ide
LayoutInflater->inflate
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;
// 循环查找顶节点
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
// 先生成顶节点布局
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.
// 实例化全部子View，以temp顶节点为父布局，递归生成View树
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) {
// 将生成的View树添加到root父布局上，
// setContentView时这里的root是mContentParent
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) {
// 若是root根视图为空，则返回在XML中找到的顶视图
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; } } 复制代码
先说下这个方法的总体流程，首先，循环上面解析好的布局资源XmlResourceParser对象，取出布局的根节点，调用createViewFromTag方法先生成根节点View。而后再调用rInflateChildren方法递归的生成整个布局View树。最后将生成的View树添加到DecorView的root根布局上。布局
先来看下createViewFromTag方法是如何生成View对象的。post
LayoutInflater->createViewFromTag
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;
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 {
// 生成View对象
if (-1 == name.indexOf('.')) {
// Android系统自带View
view = onCreateView(parent, name, attrs);
} else {
// 自定义View
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;
}
}
复制代码
这里正常状况下，最后会调用onCreateView或createView方法来生成View对象，这里的onCreateView方法中会为View的节点名添加"android.view."前缀，而后再调用createView方法生成View对象。作这一步操做是由于createView方法是经过反射生成的对象，因此须要完整的包名+类名，而Android系统自带的View都是放在android.view包下。动画
LayoutInflater->createView
protected View onCreateView(View parent, String name, AttributeSet attrs)
throws ClassNotFoundException {
return onCreateView(name, attrs);
}
protected View onCreateView(String name, AttributeSet attrs)
throws ClassNotFoundException {
return createView(name, "android.view.", attrs);
}
public final View createView(String name, String prefix, AttributeSet attrs)
throws ClassNotFoundException, InflateException {
// 获取静态全局变量中是否有缓存相应的构造方法
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 // 经过反射机制获取View的Class对象 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); } } // 获取构造方法，用于View的实例化 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 // 经过反射机制获取View的Class对象 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; // 实例化View对象 final View view = constructor.newInstance(args); if (view instanceof ViewStub) { // Use the same context when inflating ViewStub later. final ViewStub viewStub = (ViewStub) view; // 若是是ViewStub 就为其设置LayoutInflater 以便后续inflate 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); } } 复制代码
createView中先是经过ClassLoader的反射机制，获取到对应的Class对象，而后获取到它的构造方法。最后经过构造方法实例化这个View对象并返回。
这就是createViewFromTag生成View对象的流程。最后咱们来看LayoutInflater->inflate中的rInflateChildren方法是如何生成View树的。
LayoutInflater->rInflateChildren
final void rInflateChildren(XmlPullParser parser, View parent, AttributeSet attrs,
boolean finishInflate) throws XmlPullParserException, IOException {
rInflate(parser, parent, parent.getContext(), attrs, finishInflate);
}
void rInflate(XmlPullParser parser, View parent, Context context,
AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {
final int depth = parser.getDepth();
int type;
boolean pendingRequestFocus = false;
while (((type = parser.next()) != XmlPullParser.END_TAG ||
parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
if (type != XmlPullParser.START_TAG) {
continue;
}
final String name = parser.getName();
if (TAG_REQUEST_FOCUS.equals(name)) {
pendingRequestFocus = true;
consumeChildElements(parser);
} else if (TAG_TAG.equals(name)) {
parseViewTag(parser, parent, attrs);
} else if (TAG_INCLUDE.equals(name)) {
if (parser.getDepth() == 0) {
throw new InflateException("<include /> cannot be the root element");
}
parseInclude(parser, context, parent, attrs);
} else if (TAG_MERGE.equals(name)) {
throw new InflateException("<merge /> must be the root element");
} else {
// 生成View对象
final View view = createViewFromTag(parent, name, context, attrs);
// 父布局
final ViewGroup viewGroup = (ViewGroup) parent;
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
// 递归调用rInflateChildren，递归生成View树
rInflateChildren(parser, view, attrs, true);
viewGroup.addView(view, params);
}
}
if (pendingRequestFocus) {
parent.restoreDefaultFocus();
}
if (finishInflate) {
parent.onFinishInflate();
}
}
复制代码
能够看到，方法里循环取出子节点。特殊节点这里不作分析，咱们看最后的else里。 首先先调用上面已经分析过的createViewFromTag方法生成当前的节点View对象，而后这里会把当前这个View做为父节点递归调用rInflateChildren方法，若是当前View有子节点，就会递归的生成子节点并调用addView方法层层的插入对应的父节点。最终就会生成一个完整的View树，总体的页面布局也就显现出来了。
相关文章
- 1. Android源码分析-setContentView加载布局流程
- 2. android setContentView源码分析
- 3. setContentView 加载过程分析
- 4. Android应用setContentView与LayoutInflater加载解析机制源码分析
- 5. android源码--setContentView()和LayoutInflater.inflate()源码分析
- 6. setContentView源码分析
- 7. Android setContentView()源码解析
- 8. Android setContentView源码解析
- 9. Android应用setContentView与LayoutInflater加载解析机制源码分析（转载）
- 10. Android ClassLoader加载过程源码分析
- 更多相关文章...
- • ionic 加载动作 - ionic 教程
- • ionic 加载动画 - ionic 教程
- • Git五分钟教程
- • 使用阿里云OSS+CDN部署前端页面与加速静态资源
相关标签/搜索
每日一句
-
每一个你不满意的现在，都有一个你没有努力的曾经。
欢迎关注本站公众号,获取更多信息
相关文章
- 1. Android源码分析-setContentView加载布局流程
- 2. android setContentView源码分析
- 3. setContentView 加载过程分析
- 4. Android应用setContentView与LayoutInflater加载解析机制源码分析
- 5. android源码--setContentView()和LayoutInflater.inflate()源码分析
- 6. setContentView源码分析
- 7. Android setContentView()源码解析
- 8. Android setContentView源码解析
- 9. Android应用setContentView与LayoutInflater加载解析机制源码分析（转载）
- 10. Android ClassLoader加载过程源码分析