【文章內(nèi)容簡(jiǎn)介】 you should create an AVD using the corresponding platform version (and API Level) and fully test your application. Make sure to declare a android:minSdkVersion attribute in the application39。s manifest and set its value to the API Level of the platform version. Declaring a minimum API Level If you build an application that uses APIs or system features introduced in the latest platform version, you should set the android:minSdkVersion attribute to the API Level of the latest platform version. This ensures that users will only be able to install your application if their devices are running a patible version of the Android platform. In turn, this ensures that your application can function properly on their devices. If your application uses APIs introduced in the latest platform version but does not declare a android:minSdkVersion attribute, then it will run properly on devices running the latest version of the platform, but not on devices running earlier versions of the platform. In the latter case, the application will crash at runtime when it tries to use APIs that don39。t exist on the earlier versions. Testing against higher API Levels After piling your application, you should make sure to test it on the platform specified in the application39。s android:minSdkVersion attribute. To do so, create an AVD that uses the platform version required by your application. Additionally, to ensure forwardpatibility, you should run and test the application on all platforms that use a higher API Level than that used by your application. The Android SDK includes multiple platform versions that you can use, including the latest version, and provides an updater tool that you can use to download other platform versions as necessary. To access the updater, use the android mandline tool, located in the sdk/tools directory. You can launch the Updater by using the android mand without specifying any options. You can also simply doubleclick the (Windows) or android (OS X/Linux) file. In ADT, you can also access the updater by selecting Window Android SDK and AVD Manager. To run your application against different platform versions in the emulator, create an AVD for each platform version that you want to test. For more information about AVDs, see Creating and Managing Virtual Devices. If you are using a physical device for testing, ensure that you know the API Level of the Android platform it runs. See the table at the top of this document for a list of platform versions and their API Levels. Using a Provisional API Level In some cases, an Early Look Android SDK platform may be available. To let you begin developing on the platform although the APIs may not be final, the platform39。s API Level integer will not be specified. You must instead use the platform39。s provisional API Level in your application manifest, in order to build applications against the platform. A provisional API Level is not an integer, but a string matching the codename of the unreleased platform version. The provisional API Level will be specified in the release notes for the Early Look SDK release notes and is casesensitive. The use of a provisional API Level is designed to protect developers and device users from inadvertently publishing or installing applications based on the Early Look framework API, which may not run properly on actual devices running the final system image. The provisional API Level will only be valid while using the Early Look SDK and can only be used to run applications in the emulator. An application using the provisional API Level can never be installed on an Android device. At the final release of the platform, you must replace any instances of the provisional API Level in your application manifest with the final platform39。s actual API Level integer. Filtering the Reference Documentation by API Level Reference documentation pages on the Android Developers site offer a Filter by API Level control in the topright area of each page. You can use the control to show documentation only for parts of the API that are actually accessible to your application, based on the API Level that it specifies in the android:minSdkVersion attribute of its manifest file. To use filtering, select the checkbox to enable filtering, just below the page search box. Then set the Filter by API Level control to the same API Level as specified by your application. Notice that APIs introduced in a later API Level are then grayed out and their content is masked, since they would not be accessible to your application. Filtering by API Level in the documentation does not provide a view of what is new or introduced in each API Level — it simply provides a way to view the entire API associated with a given API Level, while excluding API elements introduced in later API Levels. If you decide that you don39。t want to