#Multi-window on AOSP-5.1

##1. Features:

• Add window header and frame for each application.
• Each window can be moved, resized, switched to front/back.
• Each window frame can have shadow.
• When application window's dialog pops up, the application window still can be moved, resized, switched to front/back.
• Window header can be automatically shown/hidden, when maximized.

##2. How to do:

###2.0. Understand environments:

• Frameworks:

  Like all another desktops OS, Android have 4 levels: kernel level, middle library level, frameworks level, and application level. Frameworks is the implemantion of "frameworks level".

• Frameworks/base:

  It is the core of Frameworks. Include start/stop framework services, start/stop upper lever applications, manage various resources and provide services for upper level applications.

• APP: The application own area. It is usually an individual process. At least, it has ActiviyThread. and normally, it has one or multiple Activity. The related core objects are:

  Activity:

  Each activity can have multiple windows, one is application Window, anothers are dialog Window.

  Window:

  Each window has multiple View for display contents, and has an ViewRootImple to manage all View on APP side.

  View:

  View is the displaying unit, e.g. button, image, layout ... It can be organized as a tree by ViewGroup. The Decor View is the tree root, which is known by its' Window and ViewRootImple.

  Surface:

  For real drawing. ViewRootImpl has one Surface for drawing by each view. Hardware drawing View (TextureView) has individual Surface which will merge with normal Surface in lower-level.

• AMS:

  Activity Manager Service, it is in system service process, and manages all APP' Activity. The core related objects:

  ActivityStack:

  Each express an application. It can be focused/unfocused to switch current application window to front/back.

  Task:

  Each ActivityStack can have multiple tasks, which is a list with the history order. The latest one is used, at present.

  ActivityRecord:

  It is just the Activity in APP, each Task have multiple Activity, which is a list with the history order. The latest one is shown, at present.

• WMS:

  Window Manager Service, it is in system service process, and manages all Window. The core related objects:

  TaskStack:

  Just like ActivityStack in AMS. Its bounds is the reall application's displaying area, the bounds can be edited, so can let application window move and resize.

  TaskRecord: Just like Task in AMS.

  AppWindowToken:

  At least, it can be express the Activity in APP. It includes multiple WindowStates, ordered by displaying Z-order. One WindowState is for application, another for dialog.

  WindowState:

  Just like Window in APP. It owns a SurfaceControl to manage drawing, and communicates with ViewRootImpl in APP through Session and IWindow.

  SurfaceControl:

  For manging Surface, e.g. create/destroy, and set attribute. The Surface can be transparent or opaque, and also can have border padding.

###2.1. Window header/frame:

• mRootContent:

  Decor will load the first View as root View (mRootContent) to load the system predefined xml template, and there are 9 kinds templates.

• mParentContent:

  Each system predefined templates must provide 'content' layout (mParentContent) for loading Application defined xml template.

• Customizing:

  So we can customize the predefined templates to provide Window header/frame (e.g. add header/frame layout, adjust 'content' layout position).

• Special cases:

  Some Applications use an own View as root. For WanDouJia and QQ, we can avoid them to do so, but for WeChat, it won't work, so we have to be sure its border always within Window frame.

###2.2. Window operation:

• By changing the bounds in WMS, we can move and resize the application Window.

• By focusing/unfocusing the ActivityStack in AMS, we can let application Window in front/back.

• Add listener for related View in APP, so can catch all events (move, resize, or front/back ...). But in fact, in WMS, we can perform the same thing too (we will use it, next).

###2.3. Frame shadow:

• By custom drawing the Decor background and changing predefined template, we can add shadow (current implementation). But we cann't adjust background color correctly for all applications.

• Use Surface bording padding, we can add shadow, too. It need not consider about the applications background color, we will implement it in this way, next.

• For hardware drawing View, when Surface has transparent plane, it will display half-transparent video. We can mix an opaque stream (e.g. background color) to solve this issue temporarily.

###2.4. Popup dialog:

• By limiting the WindowState in WMS, we can limit the dialog window size and position. But now, we still limit the dialog size in APP side. Next, we will limit it in WMS side.

• By catching events in WMS instead of in APP, we can perform all window operation when application window has pop up dialog. But our current implementation has bugs to be fix.

###2.5. Show/Hide automatically:

• By View.setVisibility method, we can dynamically show/hide the window header layout, when toggle maximize/restore application window.

• By catching events in WMS, we can catch the event when we need show/hide the window header layout, when maximized.

• By ViewGroup.addView/ViewGroup.removeView, we can let window header display in front of the application window's original header, when maximized.

###3. Current status:

• Finish window header and frame (100%), also include each special cases, e.g. QQ, WeChat, and WanDouJia.

• Finish window operation (100%), but still can be improved, e.g. consider about pop up dialog together.

• Almost finish frame shadow (90%). Current design isn't quite common (need guessing some of application's background color). Next, we need draw shadow images on surface padding area at WMS.

• Finish part of pop up dialog (65%): Current design is correct, but the implementation isn't completed, so some of features can't work. We need completely implement dialog with frame operation at WMS.

• Do not support show/hide automatically (0%): We know how to do, and next, we shall finish it.

Thanks.

Chen Gang chengang@emindsoft.com.cn