【導讀】越來越完善，移動設備的系統(tǒng)平臺也日漸火熱起來。目前國內最常見的移動開發(fā)。平臺有Symbian，iPhone，WindowsPhone以及當下正在逐步興起的Android。前為止國內已經(jīng)有很多Android系統(tǒng)的用戶。截止2020年第二季度Android系統(tǒng)。仍然屬于起步和探索階段。急需要大量的相關技術和人員的投入。下面首先介紹一下Android系統(tǒng)。Android是基于Linux內核的軟件平臺和操。作系統(tǒng)，是Google在2020年11月5日公布的手機系統(tǒng)平臺，早期由Google開發(fā)，它采用了軟件堆層（Softwarestack，又名以。軟件疊層）的架構，主要分為三部分。低層以Linux核心工作為基礎，只提供基本。功能；其他的應用軟件則由各公司自行開發(fā)，以Java作為編寫程式的一部分。在國內Android相關領域屬于較早研究的一。四年的學習交上一份圓滿的答卷。目前國外各軟硬件廠商已經(jīng)推出過多款手機操作系統(tǒng)。目前國內還沒有自主研發(fā)并商品化的手機操作系統(tǒng)。在2020年8月，由中國移動所主導開發(fā)OPhone平臺面世。歌針對android系統(tǒng)用戶所開發(fā)的應用商場）上已經(jīng)有過萬的企業(yè)應用辦公套件。

　　

【正文】 fnes one activity per “screen.” Activities start each other, possibly passing and returning values. Only one activity 浙江大學城市學院畢業(yè)論文 外文翻譯 on the system has keyboard and ocessing focus at a time。 all others are ponents perform background processing. When an activity needs to perform some operation that must continue after the user interface disappears (such as download a fle or play music), it monly starts a service specifcally designed for that action. The developer can also use services as applicationspecifc daemons, possibly starting on boot. Services often define an interface for Remote Procedure Call (RPC) that other system ponents can use to send mands and retrieve data, as well as register callbacks. Content provider ? ponents store and share data using a relational database interface. Each content provider has an associated “authority” describing the content it contains. Other ponents use the authority name as a handle to perform SQL queries (such as SELECT, INSERT, or DELETE) to read and write content. Although content providers typically store values in database records, data retrieval is implementationspecifc—for example, fles are also shared through content provider receiver? ponents act as mailboxes for messages from other applications. Commonly, application code broadcasts messages to an implicit destination. Broadcast receivers thus subscribe to such destinations to receive the messages sent to it. Application code can also address a broadcast receiver explicitly by including the namespace assigned to its containing application. Figure 1 shows the FriendTracker and FriendViewer applications containing the diferent ponent types. The developer specifes ponents using a manifest fle (also used to defne policy as described later). There are no restrictions on the number of ponents an application defnes for each type, but as a convention, one ponent has the same name as the application. Frequently, this is an activity, as in the FriendViewer application. This activity usually indicates the primary activity that the system application launcher uses to start the user interface。 however, the specifc activity chosen on launch is marked by meta information in the manifest. In the FriendTracker application, for example, the FriendTrackerControl activity is marked as the main user interface entry point. In this case, we reserved the name “FriendTracker” for the service ponent performing the core application FriendTracker application contains each of the four ponent types. The FriendTracker service polls an external service to discover friends? locations. In our example code, we generate locaFriendTracker application BootReceiver Broadcast receiver ActivityFriendTracker FriendProvider Content provider Service FriendTracker control FriendViewer application FriendReceiver Broadcast receiver Activity FriendTracker Activity FriendViewer Figure 1. Example Android application. The 浙江大學城市學院畢業(yè)論文 外文翻譯 FriendTracker and FriendViewer applications consist of multiple ponents of different types, each of which provides a different set of functionalities. Activities provide a user interface, services execute background processing, content providers are data storage facilities, and broadcast receivers act as mailboxes for messages from other randomly, but extending the ponent to interface with a Web service is straightforward. The FriendProvider content provider maintains the most recent geographic coordinates for friends, the FriendTrackerControl activity defnes a user interface for starting and stopping the tracking functionality, and the BootReceiver broadcast receiver obtains a notifcation from the system once it boots (the application uses this to utomatically start the FriendTracker service).The FriendViewer application bis primarily concerned with showing information about friends? locations. The FriendViewer activity lists all friends and their geographic coordinates, and the FriendMap activity displays them on a map. The FriendReceiver broadcast receiver waits for messages that indicate the physical phone is near a particular friend and displays a message to the user upon such an event. Although we could have placed these ponents within the FriendTracker application, we created a separate application to demonstrate crossapplication munication. dditionally, by separating the tracking and user interface logic, we can create alternative user inter faces with different displays and features—that is, many applications can reuse the logic performed in Interaction The primary mechanism for ponent interaction is an intent, which is simply a message object containing a destination ponent address and data. The Android API defnes methods that accept intents, and uses that information to start activities (startActivity(Intent)), start services (startService (Intent)), and broadcast messages (sendBroadcast(Intent)). The invocation of these methods tells the Android framework to begin executing code in the target application. This process of interponent munication is known as an action. Simply put, an intent object defnes the “intent” to perform an “action.”O(jiān)ne of Android?s most powerful features is the fexibility allowed by its intentaddressing mechanism. Although developers can uniquely address a target ponent using its application?s namespace, they can also specify an implicit name. In the latter case, the system determines the best ponent for an action by considering the set of installed applications and user choices. The implicit name is called an action string because it specifes the type of requested action—for example, if the “VIEW” action string is specifed in an intent with data felds pointing to an image fle, the system will 浙江大學城市學院畢業(yè)論文