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1、Android API LevelsAs you develop your application on Android, its useful to understand the platforms general approach to API change management. Its also important to understand the API Level identifier and the role it plays in ensuring your applications compatibility with devices on which it may be
2、installed.The sections below provide information about API Level and how it affects your applications.For information about how to use the Filter by API Level control available in the API reference documentation, seeFiltering the documentationat the end of this document.What is API Level?API Level i
3、s an integer value that uniquely identifies the framework API revision offered by a version of the Android platform.The Android platform provides a framework API that applications can use to interact with the underlying Android system. The framework API consists of: A core set of packages and classe
4、s A set of XML elements and attributes for declaring a manifest file A set of XML elements and attributes for declaring and accessing resources A set of Intents A set of permissions that applications can request, as well as permission enforcements included in the systemEach successive version of the
5、 Android platform can include updates to the Android application framework API that it delivers.Updates to the framework API are designed so that the new API remains compatible with earlier versions of the API. That is, most changes in the API are additive and introduce new or replacement functional
6、ity. As parts of the API are upgraded, the older replaced parts are deprecated but are not removed, so that existing applications can still use them. In a very small number of cases, parts of the API may be modified or removed, although typically such changes are only needed to ensure API robustness
7、 and application or system security. All other API parts from earlier revisions are carried forward without modification.The framework API that an Android platform delivers is specified using an integer identifier called API Level. Each Android platform version supports exactly one API Level, althou
8、gh support is implicit for all earlier API Levels (down to API Level 1). The initial release of the Android platform provided API Level 1 and subsequent releases have incremented the API Level.The following table specifies the API Level supported by each version of the Android platform.Platform Vers
9、ionAPI LevelAndroid 3.011Android 2.3.310Android 2.39Android 2.28Android 2.17Android 2.0.16Android 2.05Android 1.64Android 1.53Android 1.12Android 1.01Uses of API Level in AndroidThe API Level identifier serves a key role in ensuring the best possible experience for users and application developers:
10、It lets the Android platform describe the maximum framework API revision that it supports It lets applications describe the framework API revision that they require It lets the system negotiate the installation of applications on the users device, such that version-incompatible applications are not
11、installed.Each Android platform version stores its API Level identifier internally, in the Android system itself.Applications can use a manifest element provided by the framework API to describe the minimum and maximum API Levels under which they are able to run, as well as the preferred API Level t
12、hat they are designed to support. The element offers three key attributes: android:minSdkVersion Specifies the minimum API Level on which the application is able to run. The default value is 1. android:targetSdkVersion Specifies the API Level on which the application is designed to run. In some case
13、s, this allows the application to use manifest elements or behaviors defined in the target API Level, rather than being restricted to using only those defined for the minimum API Level. android:maxSdkVersion Specifies the maximum API Level on which the application is able to run.Important:Please rea
14、d thedocumentation before using this attribute.For example, to specify the minimum system API Level that an application requires in order to run, the application would include in its manifest aelement with aandroid:minSdkVersionattribute. The value ofandroid:minSdkVersionwould be the integer corresp
15、onding to the API Level of the earliest version of the Android platform under which the application can run.When the user attempts to install an application, or when revalidating an appplication after a system update, the Android system first checks theattributes in the applications manifest and com
16、pares the values against its own internal API Level. The system allows the installation to begin only if these conditions are met: If aandroid:minSdkVersionattribute is declared, its value must be less than or equal to the systems API Level integer. If not declared, the system assumes that the applica
