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COM594: Mobile Technology Lecture – Week 8 Smartphone Architecture and Mobile Apps Android (Google) Open Source The OS Architecture is a stack of software components using a layered abstraction mechanism Android Architecture Application Layer The User-Interaction Layer: Top layer of the Stack: The Software Developer’s chief interaction at this layer is Testing: Several standard applications come installed with every device, such as: • SMS client app • Dialer • Web browser • Contact manager Application Framework Key functionality: • Activity Manager: Manages the Activity Life-cycle of the Application: • Content Providers: Manage data-sharing between applications. • Telephony Manager: Manages Voice Calls • Location Manager: Location management: GPS or Cell-tower or other AP • Resource Manager: manages all of the resources needed to support a project • Static code content, bitmaps, colours, Layout definitions, animation, etc. Library Layer The Native Libraries comprise the software needed to allow the phone to deal with different types of data. For example, the Media Framework Library provides the support for the recording and playback of various audio and video file formats. Open Source Libraries Surface Manager: Used for compositing Windows Manager with off-screen buffering. Off-screen-buffering means you CAN’T directly draw on the screen, but your drawings go to the off-screen buffer where they can be combined with other drawings to form the final screen the user will see. This buffer is the reason behind the transparency of windows. Open GL/ES & SGL: Used to render 3D and 2D graphics on the screen (respectively). Media Framework: Supports playback and recording of various audio, video and picture formats. Open Source Libraries Free Type: is used as font renderer SSL: used to communicate with a server using these secure network protocols SQLite: Database Engine used in Android Webkit: Is the browser engine used to display HTML libc: Is a derivation of the standard C library code that was originally developed by Google for their Android operating system based on the Linux kernel. It is the System’s C library. The Android Runtime On the same layer as the libraries, the Android Runtime Layer includes a set of Core Java Libraries. Android Apps are constructed via Java. The Runtime includes the Dalvik Virtual Machine The Dalvik Virtual Machine The Dalvik Virtual Machine (2) • • • • • • • • The Runtime comprises the DVM and the core libraries The DVM is a type of JVM It is optimized for low processing power It is optimized for low memory environments It Runs .dex files (Not .class files) .dex files are built from .class files at compile time DVM supports multiple instances of the VM It implements support for: Security; Isolation; Memory Management; Threading Architecture including Hardware Abstraction Layer Hardware Abstraction Layer The hardware Abstraction Layer is conceptually between the Libraries and the Kernel. It is essentially the lowest layer which the developer accesses. This layer provides a software abstraction of the physical hardware and provides the access point for an apps hardware implementation. The Kernel Layer Essentially the interface to the hardware: The key functions of the kernel are: • Hardware Abstraction; • Memory Management; • Security Management; • Power Management • Hardware Drivers; • Shared-Library support; • The network Stack The Kernel is never accessed directly by the developer. Access is via the hardware Abstraction layer Android Kernel Evolution Android Version 4.4-4.4.4 KitKat: Android Version 5.0-5.1 Lollipop API 20 API 21 More detail at: http://en.wikipedia.org/wiki/Android_version_history Hardware The primary Hardware Platform supporting Android is the 32-bit ARMv7 architecture: Intel began providing microprocessors for Android in 2012 Architecture and Apps Hardware designed to maintain low power: Apps not in use are suspended automatically Suspended apps do not consume power Apps do not require closing and reopening Automatic memory management If memory gets low, inactive apps (and processes) get ‘killed’ in ‘oldest-first’ order; Memory Management The process is supposed to be transparent to the user Lack of care by developers has resulted in ‘task-Killer’ apps on the market. ?? Open Source Android Development is done ‘in private’ by Google until release: Then the source code is made public Source code is subsequently modified by OEMs. (original equipment manufacturers) Source code does NOT contain proprietary device drivers Google Upgrade Policy Upgrades are typically every 9 or 10 Months Upgrades are slow to roll-out to devices (compared to iOS) This is true for devices not under the Nexus brand This delay is partly due to the extensive variation in hardware of Android devices, to which each upgrade must be tailored. Manufactures implement policy on updates: official Google source code only runs on their flagship Nexus devices. Google Upgrade Policy Manufactures implement policy on updates (cont’d): Porting Android to specific hardware is a time- and resourceconsuming process for device manufacturers, who prioritize their newest devices and often leave older ones behind Older smartphones are frequently not updated if the manufacturer decides it is not worth their time, regardless of whether the phone is capable of running the update Also, A view persists that not upgrading will incentivise the move to new devices Difficult for App Developers to maintain quality of provision in such circumstances? Impact of Wireless on Upgrade Policy Additional delays can be introduced by wireless carriers who, after receiving updates from manufacturers, further customize and brand Android to their needs They then conduct extensive testing on their networks before sending the upgrade out to users These typically take longer to test and evaluate. Google Play Services In 2012, Google began decoupling core applications from the Kernel The objective was that they could be updated independently from Android OS Google Play Services: A system-level process which provides APIs for Google Services. Essentially enables new OS functionality to be added without a complete OS update. Contribute to the Android Open Source Project (AOSP) Companies and Individuals can contribute to Android Development through AOSP Largest contributors are Device and chipset manufactures Google has the final say! To join in, visit the Android contribution discussion: https://groups.google.com/forum/?fromgroups#!forum/android-contrib AOSP Want to fix a bug? Visit the issue tracker: https://code.google.com/p/android/issues/list Contributions are described in detail at http://source.android.com/source/contributing.html AOSP Quality Control Contributions must comply with the Android Code Style Guidelines http://source.android.com/source/code-style.html Be patient Google get a huge number of contributions Most submissions never make it Some do but Google are very careful The next slide shows the Workflow of a patch- Designing Stable and Responsive Mobile Applications (1) Don’t perform resource intensive operations on the main UI thread. Always use asynchronous tasks or threads to offload blocking operations Use efficient data structures and algorithms Responsive aps = happy users Use recursion with care Never use recursion unless it is absolutely necessary Recursion is never absolutely necessary Designing Stable and Responsive Mobile Applications (2) Save your state and assume that your application will be stopped or suspended at any moment If your application is suspended or closed, you cannot expect the user to do anything (click a button, or whatever! Ensure that your application can resume gracefully Designing Stable and Responsive Mobile Applications (3) Start up fast and Resume fast You cannot afford to have the user waiting (Mostly they won’t) During long operations, inform the user by using progress bars Consider offloading heavy processing to a server instead of processing on the device Better performance Saves battery drainage Designing Stable and Responsive Mobile Applications (4) Ensure that long operations are likely to succeed before embarking upon them For example, if your application downloads large files, check for network connectivity, file size, and available space before attempting the download Designing Stable and Responsive Mobile Applications (5) Minimize use of local storage Most devices have very limited amounts Use external storage Remember that an SD card is ‘external storage’ Remember also that SD cards can be ejected Remember also that SD cards can be swapped Your app should handle all of these scenario’s gracefully Designing Stable and Responsive Mobile Applications (6) Understand that data calls to content providers (and across the Android Interface Definition Language (AIDL) boundary) have a performance ‘hit’ so use judiciously http://developer.android.com/guide/components/aidl.html Establish an application resource-consumption model and verify that this matches your target audience. Gamers might reasonably anticipate and accept shorter battery life Productivity app users will expect lightweight power drainage and in any case won’t always carry a charger! Common mistakes in app development Trusting the emulator You must test on a real device Forgetting to add new application activities and required permissions to the AndroidManifest.xml file Forgetting to display Toast messages using the show() method Hard-coding information, such as network info, test user information and other data into the application Forgetting to disable diagnostic logging before release Distributing live applications with debug enabled Design for Easy Upgrades and Updates Updates: Modifying manifest information and redeploying the updated application on user devices Schedule updates so that they are frequent enough to be useful, but not so frequent that the user is constantly interrupted You must have an update strategy Upgrading: Creating a new application package with new features, and deploying it as a separate application that the user must choose to install