我们的Activity通常继承自Activity或者AppCompatActivity，这两个setContentView流程是不同的
一、继承自Activity
1、Activity.setContentView
Activity中setContentVIew调用了getWindow().setContentView(view, params);
getWindow返回的是mWindow，mWindow是PhoneWindow对象，在attach中初始化
当创建Activity、Dialog、PopupWindow、Toast时都会创建PhoneWindow对象
2、PhoneWindow.setContentView
该方法主要目的是创建DecorView 拿到Content
2.1 installDecor
在installDecor方法中创建DecorView并拿到Content：
generateDecor创建DecorView
generateLayout较长，用于生成和配置窗口（Activity 的视图容器）的布局和样式。
上图红框为两行较为重要的代码
onResourcesLoaded是将上面的R.layout.simple等这种layout添加到DecorView中
第二个红框是拿到ViewGroup对象，最后返回的就是这个对象
在这之上，该方法会加载一些layout，以最简单的screen_simple举例
注意：DecorView其实就是个FrameLayout，是整个窗口的根视图，它包括应用程序内容的视图以及窗口可能有的系统级视图，如状态栏和导航栏。
其中ID为content的FrameLayout就是mContentParent
二、继承自AppCompatActivity
1、AppCompatActivity.setContentView
与继承自Activity的不同，这里是调用的AppCompatDelegate的setContentView
AppCompatDelegate是一个接口，具体实现在AppCompatDelegateImpl：
1.1、ensureSubDecor
调用ensureSubDecor，下面的与继承Activity的类似
ensureSubDecor又调用createSubDecor
createSubDecor又调用ensureWindow，ensureWindow是对window对象检查，给mWindow变量赋值，之后执行getDecorView
此时mWindow是一个PhoneWindow对象，调用PhoneWindow的getDecorView
getDecorView中又调用了installDecor，这个方法在继承Activity中出现过，此后流程不再赘述
crateDecor之后还会去获取subDecor，看最简单的abc_screen_simple
abc_screen_content_include.xml
此时subDecor有布局了
之后会通过findViewById去获取上面的ContentFrameLayout
之后执行final ViewGroup windowContentView = (ViewGroup) mWindow.findViewById(android.R.id.content);
该处获取的是Activity的，也就是R.layout.screen_simple的content
之后将这个原始的content id置为NO_ID 将subDecerView的id置为content 进行一个替换
三、LayoutInflater.from(mContext).inflate(resId, contentParent);
不管是继承自Activity还是AppCompatActivity的setContentVIew，之后都会调用这么一句代码，该代码就是创建R.layout.main_activity的View
调用res.getLayout进行xml解析
调用inflate进行渲染
java
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 {
advanceToRootNode(parser); //寻找根节点
final String name = parser.getName(); //节点名称
if (DEBUG) {
System.out.println("**************************");
System.out.println("Creating root view: "
+ name);
System.out.println("**************************");
}
//处理merge标签
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
//创建根视图
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
//处理布局参数
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.
//解析并创建子视图，该方法是一个递归方法
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(
getParserStateDescription(inflaterContext, attrs)
+ ": " + 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;
}
}1、createViewFromTag
红框中会判断name中是否有点，有执行onCreateView没有执行createView
有点一般的就是一些第三方组件或者自定义组件，比如androidx.constraintlayout.widget.ConstraintLayout
Layoutinflater是一个抽象类，onCreateView的具体实现在其实现类PhoneLayoutInflater
在onCreateView中，最终还是调用了createView
此处的prefix是一些前缀，用于在调用createView时进行补全
最后返回了super.onCreateView,父类的onCreateView中补全了android.view
然后看createView
java
@Nullable
public final View createView(@NonNull Context viewContext, @NonNull String name,
@Nullable String prefix, @Nullable AttributeSet attrs)
throws ClassNotFoundException, InflateException {
Objects.requireNonNull(viewContext);
Objects.requireNonNull(name);
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
//由于前面补全了前缀，所以这个可以通过包名进行反射，然后创建View对象
clazz = Class.forName(prefix != null ? (prefix + name) : name, false,
mContext.getClassLoader()).asSubclass(View.class);
if (mFilter != null && clazz != null) {
boolean allowed = mFilter.onLoadClass(clazz);
if (!allowed) {
failNotAllowed(name, prefix, viewContext, attrs);
}
}
//获取构造对象
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 = Class.forName(prefix != null ? (prefix + name) : name, false,
mContext.getClassLoader()).asSubclass(View.class);
boolean allowed = clazz != null && mFilter.onLoadClass(clazz);
mFilterMap.put(name, allowed);
if (!allowed) {
failNotAllowed(name, prefix, viewContext, attrs);
}
} else if (allowedState.equals(Boolean.FALSE)) {
failNotAllowed(name, prefix, viewContext, attrs);
}
}
}
Object lastContext = mConstructorArgs[0];
mConstructorArgs[0] = viewContext;
Object[] args = mConstructorArgs;
args[1] = attrs;
try {
//执行构造，创建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;
viewStub.setLayoutInflater(cloneInContext((Context) args[0]));
}
return view;
} finally {
mConstructorArgs[0] = lastContext;
}
} catch (NoSuchMethodException e) {
final InflateException ie = new InflateException(
getParserStateDescription(viewContext, attrs)
+ ": 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(
getParserStateDescription(viewContext, attrs)
+ ": 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(
getParserStateDescription(viewContext, attrs) + ": Error inflating class "
+ (clazz == null ? "<unknown>" : clazz.getName()), e);
ie.setStackTrace(EMPTY_STACK_TRACE);
throw ie;
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}到这里rootView创建好了，之后要创建子View
2、rInflateChildren
rInflateChildren调用的是rinflate
java
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;
//循环解析XML
while (((type = parser.next()) != XmlPullParser.END_TAG ||
parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
//跳过非开始标签
if (type != XmlPullParser.START_TAG) {
continue;
}
//获取标签名称
final String name = parser.getName();
//处理<requestFocus>标签
if (TAG_REQUEST_FOCUS.equals(name)) {
pendingRequestFocus = true;
consumeChildElements(parser);
} else if (TAG_TAG.equals(name)) {//处理<tag>标签
parseViewTag(parser, parent, attrs);
} else if (TAG_INCLUDE.equals(name)) {//处理<include>标签
if (parser.getDepth() == 0) {
throw new InflateException("<include /> cannot be the root element");
}
parseInclude(parser, context, parent, attrs);
} else if (TAG_MERGE.equals(name)) {//处理<merge>标签
throw new InflateException("<merge /> must be the root element");
} else {
//对于其他标签，使用createViewFromTag创建视图，生成布局参数，递归调用rInflateChildren
final View view = createViewFromTag(parent, name, context, attrs);
final ViewGroup viewGroup = (ViewGroup) parent;
final ViewGroup.LayoutParams params = viewGroup.generateLayoutParams(attrs);
rInflateChildren(parser, view, attrs, true);
viewGroup.addView(view, params);
}
}
if (pendingRequestFocus) {
parent.restoreDefaultFocus();
}
if (finishInflate) {
parent.onFinishInflate();
}
}