layoutInflater服务注册在SystemServiceRegistry中。final class SystemServiceRegistry {    static{        // ...        registerService(Context.LAYOUT_INFLATER_SERVICE, LayoutInflater.class,                new CachedServiceFetcher
    
     () {                    @Override                    public LayoutInflater createService(ContextImpl ctx) {                        return new PhoneLayoutInflater(ctx.getOuterContext());                    }});        // ...    }}// PhoneLayoutInflater继承自LayoutInflaterpublic class PhoneLayoutInflater extends LayoutInflater {    private static final String[] sClassPrefixList = {            "android.widget.",            "android.webkit.",            "android.app."    };    public PhoneLayoutInflater(Context context) {        super(context);    }    protected PhoneLayoutInflater(LayoutInflater original, Context newContext) {        super(original, newContext);    }    @Override    protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException {        for (String prefix : sClassPrefixList) {            try {                View view = createView(name, prefix, attrs);                if (view != null) {                    return view;                }            } catch (ClassNotFoundException e) {            }        }        return super.onCreateView(name, attrs);    }    public LayoutInflater cloneInContext(Context newContext) {        return new PhoneLayoutInflater(this, newContext);    }} 从Activity中setContentView(layoutResID)说起。// PhoneWindow < extend abstract class Window >public void setContentView(int layoutResID) {        // ...        if (mContentParent == null) {        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);        }        // ...}private void installDecor() {        if (mDecor == null) {            // ...            mDecor = generateDecor(-1);                // 备注 new DecorView(context, featureId, this, getAttributes()); < DecorView extends FrameLayout >        // ...        } else {            mDecor.setWindow(this);        }        if (mContentParent == null) {            mContentParent = generateLayout(mDecor);              // ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);        } }// LayoutInflaterpublic View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {       final Resources res = getContext().getResources();       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. 寻根之旅            int type;            while ((type = parser.next()) != XmlPullParser.START_TAG &&                    type != XmlPullParser.END_DOCUMENT) {                // Empty            }            final String name = parser.getName();            if (TAG_MERGE.equals(name)) {                if (root == null || !attachToRoot) {                    // InflateException                }                rInflate(parser, root, inflaterContext, attrs, false);            } else {                // 解析并创建View  final View temp = createViewFromTag(root, name, inflaterContext, attrs);                ViewGroup.LayoutParams params = null;                if (root != null) {
     params = root.generateLayoutParams(attrs);                    if (!attachToRoot) {
     temp.setLayoutParams(params);                    }                }                // 解析tmp下所有子View并添加到tmp下  rInflateChildren(parser, temp, attrs, true);   if (root != null && attachToRoot) {                    root.addView(temp, params);                }  if (root == null || !attachToRoot) {                    result = temp;                }            }        }         return result;    }}从上面源码可以看出：
    <假定根据layoutid解析并创建的view是tmp>
     1、root != null  保留tmp参数 root == null 使用默认参数赋值给tmp并返回tmp2、attachToRoot == ture && root != null; 执行 root.addView(temp, params);   attachToRoot == false tmp不会添加到root下。
    

1、解析xml中的根标签 2、如果根标签是merge，调用rInflate会将merge下所有子view添加到根标签 3、对View进行解析

void rInflate(XmlPullParser parser, View parent, Context context,        AttributeSet attrs, boolean finishInflate) throws XmlPullParserException, IOException {    final int depth = parser.getDepth();    int type;    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)) {            parseRequestFocus(parser, parent);        } else if (TAG_TAG.equals(name)) {            parseViewTag(parser, parent, attrs);        } else if (TAG_INCLUDE.equals(name)) {            if (parser.getDepth() == 0) {                throw new InflateException("
     cannot be the root element");            }            parseInclude(parser, context, parent, attrs);        } else if (TAG_MERGE.equals(name)) {            throw new InflateException("
     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 (finishInflate) {        parent.onFinishInflate();    }}