LayoutInflater

    @Override
    public void setContentView(@LayoutRes int layoutResID) {
        getDelegate().setContentView(layoutResID);
    }

@Override
public void setContentView(int resId) {
    ensureSubDecor();
    ViewGroup contentParent = mSubDecor.findViewById(android.R.id.content);
    contentParent.removeAllViews();
    LayoutInflater.from(mContext).inflate(resId, contentParent);
}

private void ensureSubDecor() {
  if (!mSubDecorInstalled) {
     mSubDecor = createSubDecor();
  }
}

private ViewGroup createSubDecor() {
    // Now let's make sure that the Window has installed its decor by retrieving it
    //确保优先初始化 DecorView  
    mWindow.getDecorView();//PhoneWindow
  
    ViewGroup subDecor = null;
  
   //根据不同的设置来对 subDecor 进行初始化  
    if (!mWindowNoTitle) {
      subDecor = title相关的view
    } else {
            if (mOverlayActionMode) {
                subDecor = (ViewGroup) inflater.inflate(
                        R.layout.abc_screen_simple_overlay_action_mode, null);
            } else {
                subDecor = (ViewGroup) inflater.inflate(R.layout.abc_screen_simple, null);
            }
    }
  
    // Now set the Window's content view with the decor
    // 将 subDecor 添加到 DecorView 中  
    mWindow.setContentView(subDecor);
    return subDecor;
}

    @Override
    public final View getDecorView() {
        if (mDecor == null || mForceDecorInstall) {
            installDecor();
        }
        return mDecor;
    }

private void installDecor() {
        if (mDecor == null) {
            mDecor = generateDecor(-1);
        } else {
            mDecor.setWindow(this);
        }
        if (mContentParent == null) {
            mContentParent = generateLayout(mDecor);
        }
}

    protected DecorView generateDecor(int featureId) {
        return new DecorView(context, featureId, this, getAttributes());
    }

protected ViewGroup generateLayout(DecorView decor) {
  ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
  return contentParent;
}

Window.java
   @Nullable
    public <T extends View> T findViewById(@IdRes int id) {
        return getDecorView().findViewById(id);
    }

View.java
    @Nullable
    public final <T extends View> T findViewById(@IdRes int id) {
        if (id == NO_ID) {
            return null;
        }
        return findViewTraversal(id);
    }

ViewGroup.java
    @Override
    protected <T extends View> T findViewTraversal(@IdRes int id) {
        if (id == mID) {
            return (T) this;
        }

        final View[] where = mChildren;
        final int len = mChildrenCount;

        for (int i = 0; i < len; i++) {
            View v = where[i];

            if ((v.mPrivateFlags & PFLAG_IS_ROOT_NAMESPACE) == 0) {
                v = v.findViewById(id);

                if (v != null) {
                    return (T) v;
                }
            }
        }

        return null;
    }

    /**
     * Obtains the LayoutInflater from the given context.
     */
    public static LayoutInflater from(Context context) {
      //对应的BinderServer是PhoneLayoutInflater,位于当前进程，不走ServiceManager获取
        LayoutInflater LayoutInflater =
                (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        return LayoutInflater;
    }

    @Override
    public Object getSystemService(@ServiceName @NonNull String name) {
        if (WINDOW_SERVICE.equals(name)) {
            return mWindowManager;
        } else if (SEARCH_SERVICE.equals(name)) {
            ensureSearchManager();
            return mSearchManager;
        }
        return super.getSystemService(name);
    }

    @Override
    public Object getSystemService(String name) {
        if (LAYOUT_INFLATER_SERVICE.equals(name)) {
            if (mInflater == null) {
                mInflater = LayoutInflater.from(getBaseContext()).cloneInContext(this);
            }
            return mInflater;
        }
        return getBaseContext().getSystemService(name);
    }

    @Override
    public Object getSystemService(String name) {
        return SystemServiceRegistry.getSystemService(this, name);
    }

        registerService(Context.LAYOUT_INFLATER_SERVICE, LayoutInflater.class,
                new CachedServiceFetcher<LayoutInflater>() {
            @Override
            public LayoutInflater createService(ContextImpl ctx) {
                return new PhoneLayoutInflater(ctx.getOuterContext());
            }});

public class PhoneLayoutInflater extends LayoutInflater {

    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();
        final XmlResourceParser parser = res.getLayout(resource);
        return inflate(parser, root, attachToRoot);
    }

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
                    // Temp is the root view that was found in the xml
                    final View temp = createViewFromTag(root, name, inflaterContext, attrs);

                    // Inflate all children under temp against its context.
                    rInflateChildren(parser, temp, attrs, true);
  
                    // 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);
                    }
}

    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 {
      
            while (((type = parser.next()) != XmlPullParser.END_TAG ||
                parser.getDepth() > depth) && type != XmlPullParser.END_DOCUMENT) {
                
                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);
              }
                
    }

    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) {
      
            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 {
                    if (-1 == name.indexOf('.')) {
                        view = onCreateView(parent, name, attrs);
                    } else {
                        view = createView(name, null, attrs);
                    }
                } finally {
                    mConstructorArgs[0] = lastContext;
                }
            }

            return view;
    }

    public final View onCreateView(View parent, String name, Context context, AttributeSet attrs) {
        return createView(parent, name, context, attrs);
    }

    @Override
    public View createView(View parent, final String name, @NonNull Context context,
            @NonNull AttributeSet attrs) {
      
          return mAppCompatViewInflater.createView(parent, name, context, attrs, inheritContext,
                IS_PRE_LOLLIPOP, /* Only read android:theme pre-L (L+ handles this anyway) */
                true, /* Read read app:theme as a fallback at all times for legacy reasons */
                VectorEnabledTintResources.shouldBeUsed() /* Only tint wrap the context if enabled */
        );

    final View createView(View parent, final String name, @NonNull Context context,
            @NonNull AttributeSet attrs, boolean inheritContext,
            boolean readAndroidTheme, boolean readAppTheme, boolean wrapContext) {
      
      // We need to 'inject' our tint aware Views in place of the standard framework versions
        switch (name) {
            case "TextView":
                view = createTextView(context, attrs);
                verifyNotNull(view, name);
                break;
            case "ImageView":
                view = createImageView(context, attrs);
                verifyNotNull(view, name);
                break;
            case "Button":
                view = createButton(context, attrs);
                verifyNotNull(view, name);
                break;
            ......
        }
        if (view == null && originalContext != context) {
            // If the original context does not equal our themed context, then we need to manually
            // inflate it using the name so that android:theme takes effect.
            view = createViewFromTag(context, name, attrs);
        }
    }
      
     @NonNull
    protected AppCompatButton createButton(Context context, AttributeSet attrs) {
        return new AppCompatButton(context, attrs);
    }

    private View createViewFromTag(Context context, String name, AttributeSet attrs) {
          createViewByPrefix(context, name, null)
    }

    private View createViewByPrefix(Context context, String name, String prefix)
            throws ClassNotFoundException, InflateException {
            Constructor<? extends View> constructor = sConstructorMap.get(name);
            if (constructor == null) {
                // Class not found in the cache, see if it's real, and try to add it
                Class<? extends View> clazz = Class.forName(
                        prefix != null ? (prefix + name) : name,
                        false,
                        context.getClassLoader()).asSubclass(View.class);

                constructor = clazz.getConstructor(sConstructorSignature);
                sConstructorMap.put(name, constructor);
            }
            constructor.setAccessible(true);
            return constructor.newInstance(mConstructorArgs);
 }

    public void setFactory2(Factory2 factory) {
        if (mFactorySet) {
            throw new IllegalStateException("A factory has already been set on this LayoutInflater");
        }
        mFactorySet = true;
        if (mFactory == null) {
            mFactory = mFactory2 = factory;
        } else {
            mFactory = mFactory2 = new FactoryMerger(factory, factory, mFactory, mFactory2);
        }
    }