1. 分析入口为Activity onCreate调用的 setContentView(..)方法
//Activity类
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
2.Activity类中 setContentView(..)调用了 getWindow().setContentView(layoutResID), getWindow()获取了一个Window对象并调用了Window对象的setContentView（）方法
//Activity类
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
Window： 顶级窗口外观和行为策略的抽象基类。这个类的一个实例应该被用作添加到窗口管理器的顶层视图。它提供了标准的UI策略，如背景，标题区域，默认密钥处理等。
3.Window对象是一个抽象了他的唯一实现是PhoneWindow 其中setContentView（...）才是关键
//PhoneWindow类
public void setContentView(int layoutResID) {
if (mContentParent == null) {//mContentParent ViewGroup 视图容器 判断是否为空 实际是 DecorView 这是顶View
installDecor();//初始化DecorView 设置Activity主题
} else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {//没有动画移除所有View
mContentParent.removeAllViews();//移除视图
}
if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {//有过度动画 执行动画
final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
getContext());
transitionTo(newScene);
} else {//初始化布局
mLayoutInflater.inflate(layoutResID, mContentParent);//解析XML 添加View
}
mContentParent.requestApplyInsets();
final Callback cb = getCallback();
if (cb != null && !isDestroyed()) {
cb.onContentChanged();
}
mContentParentExplicitlySet = true;
}
3.1 初始化顶层容器DecorView 初始化后还要设置当前界面 style（样式）添加初始化布局
//PhoneWindow类
private void installDecor() {
mForceDecorInstall = false;
if (mDecor == null) {//DecorView为空直接创建
mDecor = generateDecor(-1);
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
} else {
mDecor.setWindow(this);//绑定当前PhoneWindow
}
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);//设置style Activity 样式 并为DecorView初始布局样式
.....
}
}
3.2 generateLayout（）Activity style实在这里解析配置
protected ViewGroup generateLayout(DecorView decor) {
TypedArray a = getWindowStyle();//获取页面当前样式数据 方法如下：
if (false) {
System.out.println("From style:");
String s = "Attrs:";
for (int i = 0; i < R.styleable.Window.length; i++) {
s = s + " " + Integer.toHexString(R.styleable.Window[i]) + "="
+ a.getString(i);
}
System.out.println(s);
}
mIsFloating = a.getBoolean(R.styleable.Window_windowIsFloating, false);//判断当前Window是否是浮窗
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);
}
//以下都是设置style 的状态位
if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {//是否显示状态栏
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);
}
.....
int layoutResource;//布局文件id
int features = getLocalFeatures()
//根据主题不一样加载不同的布局文件
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;
}
......
mDecor.startChanging();
mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);//加载主题布局
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);//拿到加载程序员布局父容器
......
return contentParent;//返回程序员布局容器
}
//获取Style解析样式数据
public final TypedArray getWindowStyle() {
synchronized (this) {
if (mWindowStyle == null) {
mWindowStyle = mContext.obtainStyledAttributes(
com.android.internal.R.styleable.Window);
}
return mWindowStyle;
}
}
Activity布局.png
4.通过以上过程我们拿到了程序源定义布局文件 父容器 mContentParent （ViewGroup ）现在 mLayoutInflater.inflate(layoutResID, mContentParent)接卸自定义布局文件 一直追踪inflate（）方法会到达LayoutInflater类中
LayoutInflater解析xml生成view
- 先解析布局文件根节点
//LayoutInflater类
public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
final Resources res = getContext().getResources();
final XmlResourceParser parser = res.getLayout(resource);//Xml解析器
try {
return inflate(parser, root, attachToRoot);//调用下面方法
} finally {
parser.close();
}
}
//初始化布局文件根节点
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 {
//解析Xml 寻找根节点
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();//获取根节点name
if (TAG_MERGE.equals(name)) {//如果节点名merge
if (root == null || !attachToRoot) {//没有根节点 或者 不加载到父布局中 抛出异常
throw new InflateException("<merge /> can be used only with a valid "
+ "ViewGroup root and attachToRoot=true");
}
rInflate(parser, root, inflaterContext, attrs, false);//根节点为merge解析
}else{//正常节点
final View temp = createViewFromTag(root, name, inflaterContext, attrs);//生成view
ViewGroup.LayoutParams params = null;
if (root != null) {
params = root.generateLayoutParams(attrs);//调用父布局generateLayoutParams获取LayoutParams
if (!attachToRoot) {//不加入父布局直接设置参数 Adapter因为复用 是由Adapter管理不需要直接加入父布局
temp.setLayoutParams(params);//设置LayoutParams生成的View
}
rInflateChildren(parser, temp, attrs, true);//解析子节点 这个方法最终调用 rInflate（）；
if (root != null && attachToRoot) {//需要加入父布局
root.addView(temp, params);//将改节点加入父容器
}
.....
}
}
}
}
- 根节点下的字节点
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 {
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();
}
}
总的逻辑图
Activity UI加载.png
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