【導讀】各樣的應用程序，為手機增添更多豐富的功能。用戶每天都會下載安裝各種新的。以便將來在能在任何地方瀏覽。然而Android手機繁雜的文件存儲操作和應用程序。的安裝卸載成了各位“機友”的困擾，他們想在第一時間體驗最新最有趣的應用，想以最快的速度將電腦里的文件傳到手機中。大多數(shù)情況下這一切都會通過將電。域網(wǎng)的地方都能無須數(shù)據(jù)線輕松搞定。存在任何阻礙移動產(chǎn)業(yè)創(chuàng)新的專有權障礙[1]。統(tǒng)，應用之間的通用性和互聯(lián)性將在最大程度上得到保持[2]。同所有Linux內(nèi)核一樣，Android內(nèi)核是介于硬件層和軟件組之間的一個。運行時庫與各種程序庫運行時庫實質是一款Java重新設計的虛擬機。進程上，Dalvik虛擬機為它分配自有的實例。在Android中，編譯器將Java源文件轉為class文件，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)。Palm系統(tǒng)與其他手機系統(tǒng)相比在其。目前國內(nèi)還沒有自主研發(fā)并商品化的手機操作系統(tǒng)。在20xx年8月，由中國移動所主導開發(fā)OPhone平臺面世。整的電話解決方案和各類移動數(shù)據(jù)業(yè)務解決方案。

　　

【正文】 widgets (which are sometimes called gadgets), operate only in a small rectangle of the Home screen application. The majority of this book will cover application development, because that’s what most of you will be writing. Widget development is covered in Chapter 12, There’s No Place Like Home, on page 233. When someone buys an Android phone, it will e prepackaged with a number of 浙江大學城市學院畢業(yè)論文 外文翻譯 25 standard system applications, including the following: ? Phone dialer ? Email ? Contacts ? Web browser ? Android Market Using the Android Market, the user will be able to download new programs to run on their phone. That’s where you e in. By the time you finish this book, you’ll be able to write your own killer applications for Android. Now let’s take a closer look at the life cycle of an Android application. It’s a little different from what you’re used to seeing. It’s Alive! On your standard Linux or Windows desktop, you can have many applications running and visible at once in different windows. One of the windows has keyboard focus, but otherwise all the programs are equal. You can easily switch between them, but it’s your responsibility as the user to move the windows around so you can see what you’re doing and close programs you don’t need. Android doesn’t work that way. In Android, there is one foreground application, which typically takes over the whole display except for the status line. When the user turns on their phone, the first application they see is the Home application (see Figure , on the next page). When the user runs an application, Android starts it and brings it to the foreground. From that application, the user might invoke another application, or another screen in the same application, and then another and another. All these programs and screens are recorded on the application stack by the system’s Activity Manager. At any time, the user can press the Back button to return to the previous screen on the stack. From the user’s point of view, it works a lot like the history in a web browser. Pressing Back returns them to the previous page. Process != Application Internally, each user interface screen is represented by an Activity class (see Section , Activities, on page 39). Each activity has its own life cycle. An application is one or 浙江大學城市學院畢業(yè)論文 外文翻譯 26 more activities plus a Linux process to contain them. That sounds pretty straightforward, doesn’t it? But don’t get fortable yet。 I’m about to throw you a curve ball. In Android, an application can be “alive” even if its process has been killed. Put another way, the activity life cycle is not tied to the process life cycle. Processes are just disposable containers for activities. This is probably different from every other system you’re familiar with, so let’s take a closer look before moving on. Life Cycles of the Rich and Famous During its lifetime, each activity of an Android program can be in one of several states, as shown in Figure , on the next page. You, the developer, do not have control over what state your program is in. That’s all managed by the system. However, you do get notified when the state is about to change through the onXX() method calls. You override these methods in your Activity class, and Android will call them at the appropriate time: ? onCreate(Bundle): This is called when the activity first starts can use it to perform onetime initialization such as creatingthe user interface. onCreate( ) takes one parameter that is either null or some state information previously saved by the onSaveInstanceState( ) method. ? onStart( ): This indicates the activity is about to be displayed to the user. ? onResume( ): This is called when your activity can start interacting with the user. This is a good place to start animations and music. ? onPause( ): This runs when the activity is about to go into the background, usually because another activity has been launched in front of it. This is where you should save your program’s persistent state, such as a database record being edited. ? onStop( ): This is called when your activity is no longer visible to the user and it won’t be needed for a while. If memory is tight, onStop( ) may never be called (the system may simply terminate your process). ? onRestart( ): If this method is called, it indicates your activity is being redisplayed to the user from a stopped state. ? onDestroy( ): This is called right before your activity is destroyed. If memory is tight, onDestroy( ) may never be called (the system may simply terminate your process). ? onSaveInstanceState(Bundle): Android will call this method to allow the activity to save perinstance state, such as a cursor position within a text field. Usually you won’t need to override it because the default implementation saves the state for all your user interface 浙江大學城市學院畢業(yè)論文 外文翻譯 27 controls automatically. ? onRestoreInstanceState(Bundle): This is called when the activity is being reinitialized from a state previously saved by the onSave InstanceState( ) method. The default implementation restores the state of your user interface. Activities that are not running in the foreground may be stopped, or the Linux process that houses them may be killed at any time in order to make room for new activities. This will be a mon occurrence, so it’s important that your application be designed from the beginning with this in mind. In some cases, the onPause( ) method may be the last method called in your activity, so that’s where you should save any data you want to keep around for next time. In addition to managing your program’s life cycle, the Android framework provides a number of building blocks that you use to create your a