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

 private ViewGroup createSubDecor() {
        // 1、获取主题参数，进行一些设置，包括标题，actionbar 等 
        TypedArray a = .mContext.obtainStyledAttributes(styleable.AppCompatTheme);
        a.hasValue(styleable.AppCompatTheme_windowActionBar)) {
            a.recycle();
            throw new IllegalStateException("You need to use a Theme.AppCompat theme (or descendant) with this activity.");
        } else {
            if (a.getBoolean(styleable.AppCompatTheme_windowNoTitle,false)) {
                this.requestwindowFeature(1);
            } else if (a.getBoolean(styleable.AppCompatTheme_windowActionBar,1)">this.requestwindowFeature(108);
            }

            if (a.getBoolean(styleable.AppCompatTheme_windowActionBarOverlay,1)">this.requestwindowFeature(109if (a.getBoolean(styleable.AppCompatTheme_windowActionModeOverlay,1)">this.requestwindowFeature(10this.mIsFloating = a.getBoolean(styleable.AppCompatTheme_android_windowIsFloating,1)">);
            a.recycle();
             2、确保优先初始化 DecorView
            .mWindow.getDecorView();
            LayoutInflater inflater = LayoutInflater.from(.mContext);
            ViewGroup subDecor = null;
             3、根据不同的设置来对 subDecor 进行初始化
            .mWindowNoTitle) {
                if (.mIsFloating) {
                    subDecor = (ViewGroup)inflater.inflate(layout.abc_dialog_title_material,(ViewGroup));
                    this.mHasActionBar = this.mOverlayActionBar = ;
                } .mHasActionBar) {
                    TypedValue outValue = new TypedValue();
                    this.mContext.getTheme().resolveAttribute(attr.actionBarTheme,outValue,1)">true);
                    Object themedContext;
                    if (outValue.resourceId != 0) {
                        themedContext = new ContextThemeWrapper(.mContext,outValue.resourceId);
                    }  {
                        themedContext = .mContext;
                    }

                    subDecor = (ViewGroup)LayoutInflater.from((Context)themedContext).inflate(layout.abc_screen_toolbar,1)">this.mDecorContentParent = (DecorContentParent)subDecor.findViewById(id.decor_content_parent);
                    this.mDecorContentParent.setwindowCallback(.getwindowCallback());
                    .mOverlayActionBar) {
                        this.mDecorContentParent.initFeature(109);
                    }

                    .mFeatureProgress) {
                        this.mDecorContentParent.initFeature(2.mFeatureIndeterminateProgress) {
                        this.mDecorContentParent.initFeature(5);
                    }
                }
            }  {
                .mOverlayActionMode) {
                    subDecor = (ViewGroup)inflater.inflate(layout.abc_screen_simple_overlay_action_mode,1)">);
                }  {
                    subDecor = (ViewGroup)inflater.inflate(layout.abc_screen_simple,1)">);
                }

                if (VERSION.SDK_INT >= 21) {
                    ViewCompat.setonApplyWindowInsetsListener(subDecor, OnApplyWindowInsetsListener() {
                        public WindowInsetsCompat onApplyWindowInsets(View v,WindowInsetsCompat insets) {
                            int top = insets.getSystemWindowInsetTop();
                            int newTop = AppCompatDelegateImpl..updateStatusGuard(top);
                            if (top != newTop) {
                                insets = insets.replaceSystemWindowInsets(insets.getSystemWindowInsetLeft(),newTop,insets.getSystemWindowInsetRight(),insets.getSystemWindowInsetBottom());
                            }

                            return ViewCompat.onApplyWindowInsets(v,insets);
                        }
                    });
                }  {
                    ((FitwindowsViewGroup)subDecor).setonFitSystemWindowsListener( OnFitSystemWindowsListener() {
                         onFitSystemWindows(Rect insets) {
                            insets.top = AppCompatDelegateImpl..updateStatusGuard(insets.top);
                        }
                    });
                }
            }

            if (subDecor == ) {
                new IllegalArgumentException("AppCompat does not support the current theme features: { windowActionBar: " + this.mHasActionBar + ",windowActionBarOverlay: " + this.mOverlayActionBar + ",android:windowIsFloating: " + this.mIsFloating + ",windowActionModeOverlay: " + this.mOverlayActionMode + ",windowNoTitle: " + this.mWindowNoTitle + " }"this.mDecorContentParent == ) {
                    this.mTitleView = (TextView)subDecor.findViewById(id.title);
                }

                ViewUtils.makeOptionalFitsSystemWindows(subDecor);
                ContentFrameLayout contentView = (ContentFrameLayout)subDecor.findViewById(id.action_bar_activity_content);
                ViewGroup windowContentView = (ViewGroup)this.mWindow.findViewById(16908290);
                if (windowContentView != while(windowContentView.getChildCount() > 0) {
                        View child = windowContentView.getChildAt(0);
                        windowContentView.removeViewAt(0);
                        contentView.addView(child);
                    }

                    windowContentView.setId(-1);
                    contentView.setId(16908290if (windowContentView instanceof FrameLayout) {
                        ((FrameLayout)windowContentView).setForeground((Drawable));
                    }
                }
                 将 subDecor 添加到 DecorView 中
                .mWindow.setContentView(subDecor);
                contentView.setAttachListener( OnAttachListener() {
                     onAttachedFromWindow() {
                    }

                     onDetachedFromWindow() {
                        AppCompatDelegateImpl..dismisspopups();
                    }
                });
                 subDecor;
            }
        }
    }
                    

  // AppCompatDelegateImpl
  this.mWindow.getDecorView();

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

void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            // 生成 DecorView
            mDecor = generateDecor(-1);
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            }
        } else {
            // 这样 DecorView 就持有了window
            mDecor.setwindow(this);
        }
      ......
}


   protected DecorView generateDecor(int featureId) {
        // System process doesn''t have application context and in that case we need to directly use
        // the context we have. Otherwise we want the application context,so we don''t cling to the
        // activity.
        Context context;
        if (mUseDecorContext) {
            Context applicationContext = getContext().getApplicationContext();
            if (applicationContext == null) {
                context = getContext();
            } else {
                context = new DecorContext(applicationContext,getContext());
                if (mTheme != -1) {
                    context.setTheme(mTheme);
                }
            }
        } else {
            context = getContext();
        }
        return new DecorView(context,featureId,this,getAttributes());
   }

// ActivityThread
public void handleResumeActivity(IBinder token,1)">boolean finalStateRequest,1)">boolean isForward,String reason) {
        ...... 
        final int forwardBit = isForward
                ? WindowManager.LayoutParams.soFT_INPUT_IS_FORWARD_NAVIGATION : 0;

         If the window hasn''t yet been added to the window manager,1)"> and this guy didn''t finish itself or start another activity,1)"> then go ahead and add the window.
        boolean willBeVisible = !a.mStartedActivity;
        willBeVisible) {
            try {
                willBeVisible = ActivityManager.getService().willActivityBeVisible(
                        a.getActivityToken());
            } catch (remoteexception e) {
                throw e.rethrowFromSystemServer();
            }
        }
        if (r.window == null && !a.mFinished && willBeVisible) {
            r.window = r.activity.getwindow();
            View decor = r.window.getDecorView();
            decor.setVisibility(View.INVISIBLE);
            ViewManager wm = a.getwindowManager();
            WindowManager.LayoutParams l = r.window.getAttributes();
            a.mDecor = decor;
            l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
            l.softInputMode |= forwardBit;
            ......
            if (a.mVisibleFromClient) {
                a.mWindowAdded) {
                    a.mWindowAdded = ;
                    wm.addView(decor,l);
                }  {
                     The activity will get a callback for this {@link LayoutParams} change
                     earlier. However,at that time the decor will not be set (this is set
                     in this method),so no action will be taken. This call ensures the
                     callback occurs with the decor set.
                    a.onWindowAttributesChanged(l);
                }
            }

             If the window has already been added,but during resume
             we started another activity,then don''t yet make the
             window visible.
        } if (localLOGV) Slog.v(TAG,"Launch " + r + " mStartedActivity set");
            r.hideForNow = ;
        }

         Get rid of anything left hanging around.
        cleanUpPendingRemoveWindows(r,1)">false /* force */);

         The window is Now visible if it has been added,we are not
         simply finishing,and we are not starting another activity.
        if (!r.activity.mFinished && willBeVisible && r.activity.mDecor != null && !r.hideForNow) {
            if (r.newConfig != ) {
                performConfigurationChangedForActivity(r,r.newConfig);
                 (DEBUG_CONfigURATION) {
                    Slog.v(TAG,"Resuming activity " + r.activityInfo.name + " with newConfig "
                            + r.activity.mCurrentConfig);
                }
                r.newConfig = ;
            }
             isForward);
            WindowManager.LayoutParams l = r.window.getAttributes();
             ((l.softInputMode
                    & WindowManager.LayoutParams.soFT_INPUT_IS_FORWARD_NAVIGATION)
                    != forwardBit) {
                l.softInputMode = (l.softInputMode
                        & (~WindowManager.LayoutParams.soFT_INPUT_IS_FORWARD_NAVIGATION))
                        | forwardBit;
                 (r.activity.mVisibleFromClient) {
                    ViewManager wm = a.getwindowManager();
                    View decor = r.window.getDecorView();
                    wm.updateViewLayout(decor,l);
                }
            }

            r.activity.mVisibleFromServer = ;
            mNumVisibleActivities++ (r.activity.mVisibleFromClient) {
　　　　　　　　　　 这里也会调用addview
                r.activity.makeVisible();
            }
        }

        r.nextIdle = mNewActivities;
        mNewActivities = r;
         r);
        Looper.myQueue().addIdleHandler( Idler());
    }

// Activity
 makeVisible() {
        mWindowAdded) {
            ViewManager wm = getwindowManager();
            wm.addView(mDecor,getwindow().getAttributes());
            mWindowAdded = ;
        }
        mDecor.setVisibility(View.VISIBLE);
    }