【正文】 n action string that indicates battery is low). The other ponent type, content provider, is not activated by intents. Rather, it is activated when targeted by a request from a ContentResolver. The content resolver handles all direct transactions with the content provider so that the ponent that39。它是在有需求的時(shí)候啟動(dòng) 了其它應(yīng)用程序的那個(gè)功能部分。每個(gè) view均控制著窗口中一塊特定的矩形區(qū)域。系統(tǒng)將在返個(gè) activity出 再顯示于 屏幕 后，仍維持音樂(lè)播放 service的運(yùn)行。 Content provider content provider將一些特定的應(yīng)用程序數(shù)據(jù)供給其它應(yīng)用程序使用。 Android通過(guò)調(diào)用 activity的 onNewIntent()方法來(lái)傳遞給它隨后的任何 intent。 而 activity則 出 同，它提供了用戶(hù)界面。除了聲明此應(yīng)用程序各個(gè)組件，它會(huì)做很多其他工作，比如指明應(yīng)用程序所需鏈接到的庫(kù)的名稱(chēng)（除了默 認(rèn) 的 Android庫(kù)外）以及標(biāo)出應(yīng)用程序期望獲得的各種權(quán)限。 欲了解更多關(guān) 于 intent消息的信息，請(qǐng)參閱獨(dú)立文章 Intent和 Intent過(guò)濾器。而對(duì) 于 broadcast receiver來(lái)說(shuō)， Intent17 對(duì)象指明了所通報(bào)的操作。 broadcast receiver沒(méi)有用戶(hù)界面。 一個(gè)媒體播放器播放播放列表中的曲目是一個(gè) 出 錯(cuò)的例子。 每個(gè) activity都被給予一個(gè)默 認(rèn) 的窗口以行繪制。s screen orientation and size. For example, when the device screen is in portrait orientation (tall), you might want a layout with buttons to be vertical, but when the screen is in landscape orientation (wide), the buttons should be aligned horizontally. To change the layout depending on the orientation, you can define two different layouts and apply the appropriate qualifier to each layout39。t need to incorporate or even link to the code from the camera application. Instead, you can simply start the activity in the camera application that captures 6 a photo. When plete, the photo is even returned to your application so you can use it. To the user, it seems as if the camera is actually a part of your application. When the system starts a ponent, it starts the process for that application (if it39。s possible to arrange for two applications to share the same Linux user ID, in which case they are able to access each other39。s contacts. Declare the minimum API Level required by the application, based on which APIs the application uses. Declare hardware and software features used or required by the application, such as a camera, bluetooth services, or a multitouch screen. API libraries the application needs to be linked against (other than the Android framework APIs), such as the Google Maps library. Declaring ponent capabilities As discussed above, in Activating Components, you can use an Intent to start activities, services, and broadcast receivers. You can do so by explicitly naming the target ponent (using the ponent class name) in the intent. However, the real power of intents lies in the concept of intent actions. With intent actions, you simply describe the type of action you want to perform (and optionally, the data upon which you’d like to perform the action) and allow the system to find a ponent on 9 the device that can perform the action and start it. If there are multiple ponents that can perform the action described by the intent, then the user selects which one to use. The way the system identifies the ponents that can respond to an intent is by paring the intent received to the intent filters provided in the manifest file of other applications on the device. When you declare a ponent in your application39。一個(gè)短消息應(yīng)用程序可以包括一個(gè)用 于 顯示要發(fā)送消息到的聯(lián)系人列表的 activity，一個(gè)給選定的聯(lián)系人 寫(xiě)短信的 activity以及翻閱以前的短信戒改變?cè)O(shè)置的其他activity。 Android有一些預(yù)置的 view供開(kāi)發(fā)者使用 —— 包括按鈕、文本域、滾 動(dòng)條、菜單項(xiàng)、復(fù)選框等等。所以它 出 會(huì)對(duì)其它組件戒用戶(hù)界面有任何妨礙，它們一般會(huì)派生一個(gè)新線程來(lái)執(zhí)行一些時(shí)間消耗型任務(wù)（比如音樂(lè)回放）。 參閱獨(dú)立的 Content Providers文檔以獲得更多關(guān) 于 使用 content provider的信息。 以 此類(lèi)似，一個(gè) intent可以被傳遞給 ()以建立一個(gè)處 于 調(diào)用組件和目標(biāo) service乀間的活 動(dòng) 連接。一個(gè) activity可以通過(guò)調(diào)用 finishActivity()方法來(lái)關(guān)閉另外一個(gè) activity（它用startActivityForResult() 啟 動(dòng) 的）。 系統(tǒng)也會(huì)在組件 出 再被使用的時(shí)候戒者當(dāng) Android必須為更多的活 動(dòng) 組件回收內(nèi)存時(shí)關(guān)閉它。例如，一個(gè) activity可以建立一個(gè)不前述的音樂(lè)回放 service的連接，返樣它就可以提供給用戶(hù)一些途徑（用戶(hù)界面）來(lái)控制回放。 激活組件： intent 當(dāng)接收到 ContentResolver發(fā)出的請(qǐng)求后， content provider被激活。 16 Broadcast receiver broadcast receiver是一個(gè)與注 于 接收廣播通知信息，并做出相應(yīng)處理的組件。 content view是位 于 層次結(jié)構(gòu)根位置的 View對(duì)象。每一個(gè)都實(shí)現(xiàn)為以 Activity類(lèi)為基類(lèi)的子類(lèi)。s declaration element. For example, an application with an activity for posing a new might declare an intent filter in its manifest entry to respond to send intents (in order to send ). An activity in your application can then create an intent with the “send” action ( ACTION_SEND), which the system matches to the application’s “send” activity and launches it when you invoke the intent with startActivity(). For more about creating intent filters, see the Intents and Intent Filters document. Declaring application requirements There are a variety of devices powered by Android and not all of them provide the same features and capabilities. In order to prevent your application from being installed on devices that lack features needed by your application, it39。s contacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, and more. All application permissions must be granted by the user at install time. That covers the basics regarding how an Android application exists within the system. The rest of this document introduces you to: The core framework ponents that define your application The manifest file in which you declare ponents and required device features for your application. Resources that are separate from the application code and allow your application to gracefully optimize its behavior for a variety of device configurations. Application Components Application ponents are the essential building blocks