代码流程

1、先看UI显示，StatuBar加载 CollapsedStatusBarFragment 替换 status_bar_container(状态栏通知显示区域)

SystemUI\src\com\android\systemui\statusbar\phone\StatusBar.java

FragmentHostManager.get(mStatusBarWindow)
            .addTagListener(CollapsedStatusBarFragment.TAG, (tag, fragment) -> {
                CollapsedStatusBarFragment statusBarFragment =
                        (CollapsedStatusBarFragment) fragment;
                statusBarFragment.initNotificationIconArea(mNotificationIconAreaController);
                mStatusBarView = (PhoneStatusBarView) fragment.getView();
                mStatusBarView.setBar(this);
                mStatusBarView.setPanel(mNotificationPanel);
                mStatusBarView.setScrimController(mScrimController);
                mStatusBarView.setBouncerShowing(mBouncerShowing);
                setAreThereNotifications();
                checkBarModes();
                /// M: add for plmn display feature @{
                attachPlmnPlugin();
                ///@}
            }).getFragmentManager()
            .beginTransaction()
            .replace(R.id.status_bar_container, new CollapsedStatusBarFragment(),
                    CollapsedStatusBarFragment.TAG)
            .commit();

statusBarFragment.initNotificationIconArea(mNotificationIconAreaController) 初始化通知栏区域，这是我们关心的

mStatusBarView.setBar(this) 传递statusBar处理下拉事件

mStatusBarView.setPanel(mNotificationPanel) 传递 NotificationPanelView 显示下拉UI控制

2、跟进 CollapsedStatusBarFragment 中，先看布局文件 status_bar.xml

1、notification_lights_out---ImageView默认gone

2、status_bar_contents--LinearLayout

    notification_icon_area--FrameLayout

    system_icon_area--LinearLayout

            system_icons.xml(蓝牙、wifi、VPN、网卡、SIM卡信号、飞行模式等) 电池

            clock--Clock.java 

3、emergency_cryptkeeper_text--ViewStub（延迟加载 紧急电话文字）

这就是我们看到的statusBar的布局，本篇只关心 notification_icon_area，其它的以后再进行分析。继续看到之前的 initNotificationIconArea()

SystemUI\src\com\android\systemui\statusbar\phone\CollapsedStatusBarFragment.java

public void initNotificationIconArea(NotificationIconAreaController
        notificationIconAreaController) {
    ViewGroup notificationIconArea = mStatusBar.findViewById(R.id.notification_icon_area);
    mNotificationIconAreaInner =
            notificationIconAreaController.getNotificationInnerAreaView();
    if (mNotificationIconAreaInner.getParent() != null) {
        ((ViewGroup) mNotificationIconAreaInner.getParent())
                .removeView(mNotificationIconAreaInner);
    }
    notificationIconArea.addView(mNotificationIconAreaInner);
    // Default to showing until we know otherwise.
    showNotificationIconArea(false);
}

获取到 notification_icon_area，FrameLayout转为ViewGroup，调用 notificationIconAreaController 获取通知要显示的view(LinearLayout)，

如果已经有显示的view，通过 view 父布局将其自身remove，然后再重新addView。最后将 mNotificationIconAreaInner 显示出来(设置透明度为1，visibility为VISIBLE)

可以看到 CollapsedStatusBarFragment 中定义了几个如下的方法。

 public void hideSystemIconArea(boolean animate) {
    animateHide(mSystemIconArea, animate);
}

public void showSystemIconArea(boolean animate) {
    animateShow(mSystemIconArea, animate);
}

public void hideNotificationIconArea(boolean animate) {
    animateHide(mNotificationIconAreaInner, animate);
}

public void showNotificationIconArea(boolean animate) {
    animateShow(mNotificationIconAreaInner, animate);
}

当状态栏下拉时，状态栏中的图标icon会慢慢的变成透明和不可见，就是通过hideSystemIconArea(true), hideNotificationIconArea(true）

3、接下来，我们需要跟进 getNotificationInnerAreaView()方法中看看通知栏icon对应的容器

SystemUI\src\com\android\systemui\statusbar\phone\NotificationIconAreaController.java

public View getNotificationInnerAreaView() {
    return mNotificationIconArea;
}

protected void initializeNotificationAreaViews(Context context) {
    reloadDimens(context);

    LayoutInflater layoutInflater = LayoutInflater.from(context);
    mNotificationIconArea = inflateIconArea(layoutInflater);
    mNotificationIcons = (NotificationIconContainer) mNotificationIconArea.findViewById(
            R.id.notificationIcons);

    mNotificationScrollLayout = mStatusBar.getNotificationScrollLayout();
}

protected View inflateIconArea(LayoutInflater inflater) {
    return inflater.inflate(R.layout.notification_icon_area, null);
}

//notification_icon_area.xml
<com.android.keyguard.AlphaOptimizedLinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/notification_icon_area_inner"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<com.android.systemui.statusbar.phone.NotificationIconContainer
    android:id="@+id/notificationIcons"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_alignParentStart="true"
    android:gravity="center_vertical"
    android:orientation="horizontal"/>
</com.android.keyguard.AlphaOptimizedLinearLayout>

好了，观察上面的代码，现在基本上已经理清 notification_icon_area 的布局结构了

notification_icon_area(FrameLayout) 中添加 notification_icon_area_inner(LinearLayout),

每一个通知对应的bean为 NotificationData，创建 Notification 添加到 NotificationIconContainer(FrameLayout)中

4、紧接着我们就来看下 Notification 的监听加载流程，回到 statusBar 的start()中注册 NotificationListenerWithPlugins 作为系统service监听通知消息

try {
        mNotificationListener.registerAsSystemService(mContext,
                new ComponentName(mContext.getPackageName(), getClass().getCanonicalName()),
                UserHandle.USER_ALL);
    } catch (RemoteException e) {
        Log.e(TAG, "Unable to register notification listener", e);

    }

    private final NotificationListenerWithPlugins mNotificationListener =
        new NotificationListenerWithPlugins() {
    @Override
    public void onListenerConnected() {
        ......  services成功启动，获取当前处于活动状态的通知(没被移除的通知)，添加到通知栏，此处应该是重启后重新加载
    }

    @Override
    public void onNotificationPosted(final StatusBarNotification sbn,
            final RankingMap rankingMap) {
        ...... 收到通知消息，添加或者修改
        if (isUpdate) {
            updateNotification(sbn, rankingMap);
        } else {
            addNotification(sbn, rankingMap);
        }
    }

    @Override
    public void onNotificationRemoved(StatusBarNotification sbn,
            final RankingMap rankingMap) {
        ...... 移除通知消息
        if (sbn != null && !onPluginNotificationRemoved(sbn, rankingMap)) {
            final String key = sbn.getKey();
            mHandler.post(() -> removeNotification(key, rankingMap));
        }
    }

    @Override
    public void onNotificationRankingUpdate(final RankingMap rankingMap) {
        ..... 通知的排序优先级改变，修改通知位置
        if (rankingMap != null) {
            RankingMap r = onPluginRankingUpdate(rankingMap);
            mHandler.post(() -> updateNotificationRanking(r));
        }
    }

};

继续来看下 addNotification()方法

public void addNotification(StatusBarNotification notification, RankingMap ranking)
        throws InflationException {
    String key = notification.getKey();
    if (true/**DEBUG*/) Log.d(TAG, "addNotification key=" + key);
    mNotificationData.updateRanking(ranking);
    Entry shadeEntry = createNotificationViews(notification);
    ......
}

可以看到是通过 createNotificationViews()来创建通知 View对象，内部继续调用 inflateViews()

protected NotificationData.Entry createNotificationViews(StatusBarNotification sbn)
        throws InflationException {
    if (DEBUG) {
        Log.d(TAG, "createNotificationViews(notification=" + sbn);
    }
    NotificationData.Entry entry = new NotificationData.Entry(sbn);
    Dependency.get(LeakDetector.class).trackInstance(entry);
    entry.createIcons(mContext, sbn);
    // Construct the expanded view.
    inflateViews(entry, mStackScroller);
    return entry;
}

protected void inflateViews(Entry entry, ViewGroup parent) {
    PackageManager pmUser = getPackageManagerForUser(mContext,
            entry.notification.getUser().getIdentifier());

    final StatusBarNotification sbn = entry.notification;
    if (entry.row != null) {
        entry.reset();
        updateNotification(entry, pmUser, sbn, entry.row);
    } else {
        new RowInflaterTask().inflate(mContext, parent, entry,
                row -> {
                    bindRow(entry, pmUser, sbn, row);
                    updateNotification(entry, pmUser, sbn, row);
                });
    }

}

看到上面的方法中，entry在 createNotificationViews 中创建，只赋值了icons， entry.row 为null，进入 RowInflaterTask 中

SystemUI\src\com\android\systemui\statusbar\notification\RowInflaterTask.java

public void inflate(Context context, ViewGroup parent, NotificationData.Entry entry,
        RowInflationFinishedListener listener) {
    mListener = listener;
    AsyncLayoutInflater inflater = new AsyncLayoutInflater(context);
    mEntry = entry;
    entry.setInflationTask(this);
    inflater.inflate(R.layout.status_bar_notification_row, parent, this);
}

这里我们得到了 Notification 对应的layout为 status_bar_notification_row.xml，

回调方法中将 row 和 entry 绑定，继续再调用 updateNotification()，注意这个方法是四个参数的，该类中还有重载方法是两个参数的。

private void updateNotification(Entry entry, PackageManager pmUser,
        StatusBarNotification sbn, ExpandableNotificationRow row) {
    .....

    entry.row = row;
    entry.row.setOnActivatedListener(this);

    boolean useIncreasedCollapsedHeight = mMessagingUtil.isImportantMessaging(sbn,
            mNotificationData.getImportance(sbn.getKey()));
    boolean useIncreasedHeadsUp = useIncreasedCollapsedHeight && mPanelExpanded;
    row.setUseIncreasedCollapsedHeight(useIncreasedCollapsedHeight);
    row.setUseIncreasedHeadsUpHeight(useIncreasedHeadsUp);
    row.updateNotification(entry);
}

紧接着调用了 ExpandableNotificationRow的 updateNotification()，内部继续调用 NotificationInflater.inflateNotificationViews()

SystemUI\src\com\android\systemui\statusbar\notification\NotificationInflater.java

@VisibleForTesting
void inflateNotificationViews(int reInflateFlags) {
    if (mRow.isRemoved()) {
        // We don't want to reinflate anything for removed notifications. Otherwise views might
        // be readded to the stack, leading to leaks. This may happen with low-priority groups
        // where the removal of already removed children can lead to a reinflation.
        return;
    }
    StatusBarNotification sbn = mRow.getEntry().notification;
    new AsyncInflationTask(sbn, reInflateFlags, mRow, mIsLowPriority,
            mIsChildInGroup, mUsesIncreasedHeight, mUsesIncreasedHeadsUpHeight, mRedactAmbient,
            mCallback, mRemoteViewClickHandler).execute();
}

new AsyncInflationTask().execute();

@Override
protected InflationProgress doInBackground(Void... params) {
    try {
        final Notification.Builder recoveredBuilder
                = Notification.Builder.recoverBuilder(mContext,
                mSbn.getNotification());
        Context packageContext = mSbn.getPackageContext(mContext);
        Notification notification = mSbn.getNotification();
        if (mIsLowPriority) {
            int backgroundColor = mContext.getColor(
                    R.color.notification_material_background_low_priority_color);
            recoveredBuilder.setBackgroundColorHint(backgroundColor);
        }
        if (notification.isMediaNotification()) {
            MediaNotificationProcessor processor = new MediaNotificationProcessor(mContext,
                    packageContext);
            processor.setIsLowPriority(mIsLowPriority);
            processor.processNotification(notification, recoveredBuilder);
        }
        return createRemoteViews(mReInflateFlags,
                recoveredBuilder, mIsLowPriority, mIsChildInGroup,
                mUsesIncreasedHeight, mUsesIncreasedHeadsUpHeight, mRedactAmbient,
                packageContext);
    } catch (Exception e) {
        mError = e;
        return null;
    }
}

@Override
protected void onPostExecute(InflationProgress result) {
    if (mError == null) {
        mCancellationSignal = apply(result, mReInflateFlags, mRow, mRedactAmbient,
                mRemoteViewClickHandler, this);
    } else {
        handleError(mError);
    }
}

从msbn中获取 notifaction，判断是否是媒体类型的通知，进行对应的主题背景色修改，通过传递的优先级设置通知背景色，继续看核心方法 createRemoteViews()

private static InflationProgress createRemoteViews(int reInflateFlags,
        Notification.Builder builder, boolean isLowPriority, boolean isChildInGroup,
        boolean usesIncreasedHeight, boolean usesIncreasedHeadsUpHeight, boolean redactAmbient,
        Context packageContext) {
    InflationProgress result = new InflationProgress();
    isLowPriority = isLowPriority && !isChildInGroup;
    if ((reInflateFlags & FLAG_REINFLATE_CONTENT_VIEW) != 0) {
        result.newContentView = createContentView(builder, isLowPriority, usesIncreasedHeight);
    }

    if ((reInflateFlags & FLAG_REINFLATE_EXPANDED_VIEW) != 0) {
        result.newExpandedView = createExpandedView(builder, isLowPriority);
    }

    if ((reInflateFlags & FLAG_REINFLATE_HEADS_UP_VIEW) != 0) {
        result.newHeadsUpView = builder.createHeadsUpContentView(usesIncreasedHeadsUpHeight);
    }

    if ((reInflateFlags & FLAG_REINFLATE_PUBLIC_VIEW) != 0) {
        result.newPublicView = builder.makePublicContentView();
    }

    if ((reInflateFlags & FLAG_REINFLATE_AMBIENT_VIEW) != 0) {
        result.newAmbientView = redactAmbient ? builder.makePublicAmbientNotification()
                : builder.makeAmbientNotification();
    }
    result.packageContext = packageContext;
    return result;
}

这里就是创建各种布局 CONTENT_VIEW、EXPANDED_VIEW、HEADS_UP_VIEW、PUBLIC_VIEW、AMBIENT_VIEW，

然后回到 AsyncInflationTask 的 onPostExecute()中执行 apply(),代码太多就不贴了, SystemUI部分的通知流程分析技术，欢迎留言讨论。

statusBar左边区域(notification_icon_area)看完了，接下来看下右边的系统图标区域(system_icon_area)

Android8.1 SystemUI源码分析之 电池时钟刷新

从根源上屏蔽Notification

frameworks/base/services/core/java/com/android/server/notification/NotificationManagerService.java

注释如下代码

mHandler.post(new EnqueueNotificationRunnable(userId, r))