如何选择 compileSdkVersion, minSdkVersion 和 targetSdkVersion

刺骨的言语ヽ痛彻心扉 2022-06-08 08:55 165阅读 0赞

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英文原文： [Picking your compileSdkVersion, minSdkVersion, and targetSdkVersion][Picking your compileSdkVersion_ minSdkVersion_ and targetSdkVersion]

作者：Ian Lake，Google Android 推广工程师；翻译：韩国恺。

当你发布一个应用之后，(取决于具体的发布时间)可能没过几个月 Android 系统就发布了一个新版本。这对你的应用意味着什么，所有东西都不能用了？

别担心，向前兼容是 Android 非常关注的事情。用户在升级到新版 Android 的时候，用以前版本的 SDK 构建的现有应用应该不会出问题。这就是 compileSdkVersion, minSdkVersion 和 targetSdkVersion 的作用：他们分别控制可以使用哪些 API ，要求的 API 级别是什么，以及应用的兼容模式。

### compileSdkVersion ###

compileSdkVersion 告诉 Gradle 用哪个 Android SDK 版本编译你的应用。使用任何新添加的 API 就需要使用对应 Level 的 Android SDK。

需要强调的是修改 compileSdkVersion 不会改变运行时的行为。当你修改了 compileSdkVersion 的时候，可能会出现新的编译警告、编译错误，但新的 compileSdkVersion 不会被包含到 APK 中：它纯粹只是在编译的时候使用。（你真的应该修复这些警告，他们的出现一定是有原因的）

因此我们强烈推荐总是使用最新的 SDK 进行编译。在现有代码上使用新的编译检查可以获得很多好处，避免新弃用的 API ，并且为使用新的 API 做好准备。

注意，如果使用 [Support Library][] ，那么使用最新发布的 Support Library 就需要使用最新的 SDK 编译。例如，要使用 23.1.1 版本的 Support Library ，compileSdkVersion 就必需至少是 23 （大版本号要一致！）。通常，新版的 Support Library 随着新的系统版本而发布，它为系统新增加的 API 和新特性提供兼容性支持。

### minSdkVersion ###

如果 compileSdkVersion 设置为可用的最新 API，那么 minSdkVersion 则是应用可以运行的最低要求。minSdkVersion 是 Google Play 商店用来判断用户设备是否可以安装某个应用的标志之一。

在开发时 minSdkVersion 也起到一个重要角色：[lint][] 默认会在项目中运行，它在你使用了高于 minSdkVersion 的 API 时会警告你，帮你避免调用不存在的 API 的运行时问题。如果只在较高版本的系统上才使用某些 API，通常使用[运行时检查系统版本][Link 1]的方式解决。

请记住，你所使用的库，如 [Support Library][Support Library 1] 或 [Google Play services][]，可能有他们自己的 minSdkVersion 。你的应用设置的 minSdkVersion 必需大于等于这些库的 minSdkVersion 。例如有三个库，它们的 minSdkVersion 分别是 4, 7 和 9 ，那么你的 minSdkVersion 必需至少是 9 才能使用它们。在少数情况下，你仍然想用一个比你应用的 minSdkVersion 还高的库（处理所有的边缘情况，确保它只在较新的平台上使用），你可以使用 [tools:overrideLibrary 标记][tools_overrideLibrary]，但请做彻底的测试！

当你决定使用什么 minSdkVersion 时候，你应该参考当前的 [Android 分布统计][Android]，它显示了最近 7 天所有访问 Google Play 的设备信息。他们就是你把应用发布到 Google Play 时的潜在用户。最终这是一个商业决策问题，取决于为了支持额外 3% 的设备，确保最佳体验而付出的开发和测试成本是否值得。

当然，如果某个新的 API 是你整个应用的关键，那么确定 minSdkVersion 的值就比较容易了。不过要记得 14 亿设备中的 0.7％ 也是个不小的数字。

### targetSdkVersion ###

三个版本号中最有趣的就是 targetSdkVersion 了。 targetSdkVersion 是 Android 提供向前兼容的主要依据，在应用的 targetSdkVersion 没有更新之前系统不会应用最新的行为变化。这允许你在适应新的行为变化之前就可以使用新的 API （因为你已经更新了 compileSdkVersion 不是吗？）。

targetSdkVersion 所暗示的许多行为变化都记录在 [VERSION\_CODES][VERSION_CODES] 文档中了，但是所有恐怖的细节也都列在每次发布的平台亮点中了，在这个 [API Level 表][API Level]中可以方便地找到相应的链接。

例如，[Android 6.0 变化文档][Android 6.0]中谈了 target 为 API 23 时会如何把你的应用转换到[运行时权限模型][Link 2]上，[Android 4.4 行为变化][Android 4.4]阐述了 target 为 API 19 及以上时使用 [set()][set] 和 [setRepeating()][setRepeating] 设置 alarm 会有怎样的行为变化。

由于某些行为的变化对用户是非常明显的（[弃用的 menu 按钮][menu]，运行时权限等），所以将 target 更新为最新的 SDK 是所有应用都应该优先处理的事情。但这不意味着你一定要使用所有新引入的功能，也不意味着你可以不做任何测试就盲目地更新 targetSdkVersion ，请一定在更新 targetSdkVersion 之前做测试！你的用户会感谢你的。

### Gradle 和 SDK 版本 ###

所以设置正确的 compileSdkVersion, minSdkVersion 和 targetSdkVersion 很重要。如你所想， [Gradle][] 和 [Android Studio][] 都在构建系统中集成了它们。在你的模块的 build.gradle 文件中（也可以在 Android Studio 的项目结构选项中）设置：

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       3 
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       5 
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       10 
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       11 
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       12 
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    <div style="box-sizing: border-box; padding-right: 0px; padding-left: 0px; margin: 0px; white-space: pre; overflow: visible; tab-size: 4; background: none !important; border: none !important; padding-top: 5px !important; padding-bottom: 3px !important; line-height: 15px !important;"> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">android</span> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;</span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important;">compileSdkVersion</span> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important;">buildToolsVersion</span> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">defaultConfig</span> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important;">applicationId</span> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(221, 17, 68) !important;">"com.example.checkyourtargetsdk"</span> 
     </div> 
     <div style="box-sizing: border-box; font-family: inherit; background: 0px center; border: 0px; padding: 0px 5px; margin: 0px; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important;"> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important;">minSdkVersion</span> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important;">targetSdkVersion</span> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 153, 153) !important;">23</span> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important;">versionCode</span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important;">versionName</span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
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     </div> 
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     </div> 
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     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

编译时用到的 compileSdkVersion 是和构建工具版本一起设置的 Android 设置之一。其他两个稍有不同，他们在构建变体([build variant][])的那里声明。defaultConfig 是所有构建变体的基础，也是设置这些默认值的地方。你可以想象在一个更复杂的系统中，应用的某些版本可能会有不同的 minSdkVersion 。

minSdkVersion 和 targetSdkVersion 与 compileSdkVersion 的另一个不同之处是它们会被包含进最终的 APK 文件中，如果你查看生成的 AndroidManifest.xml 文件，你会看到类似下面这样的标签：

如果你在 manifest 文件中手工设置，你会发现 Gradle 在构建时会忽略它们（尽管其它构建系统可能会明确依赖它们）。

#### 综合来看 ####

如果你按照上面示例那样配置，你会发现这三个值的关系是：

<table style="box-sizing: border-box; font-size: 12px; margin-left: -20px; border-collapse: collapse !important; border-spacing: 0px !important; border: none !important; padding: 0px !important; margin-right: 0px !important; margin-bottom: 0px !important; margin-top: 0px !important; background: none !important; width: auto !important; table-layout: auto !important;"> 
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       1 
     </div> 
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   <td style="box-sizing: border-box; padding: 0px !important; font-family: Monaco, MonacoRegular, &quot;Courier New&quot;, monospace !important; vertical-align: top !important; border: 0px; margin: 0px !important; background: 0px center; width: 774px;"> 
    <div style="box-sizing: border-box; padding-right: 0px; padding-left: 0px; margin: 0px; white-space: pre; overflow: visible; tab-size: 4; background: none !important; border: none !important; padding-top: 5px !important; padding-bottom: 3px !important; line-height: 15px !important;"> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">minSdkVersion</span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
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      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">targetSdkVersion</span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&lt;=</span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="box-sizing: border-box; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">compileSdkVersion</span> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

这种直觉是合理的，如果 compileSdkVersion 是你的最大值，minSdkVersion 是最小值，那么最大值必需至少和最小值一样大且 target 必需在二者之间。

理想上，在稳定状态下三者的关系应该更像这样：

<table style="font-size:12px; margin-left:-20px; border-collapse:collapse!important; border-spacing:0px!important; border:none!important; padding:0px!important; margin-right:0px!important; margin-bottom:0px!important; margin-top:0px!important; background:none!important; width:auto!important; table-layout:auto!important"> 
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    <div style="background:0px center; border:0px; padding-right:0px; padding-left:0px; margin:0px; white-space:nowrap; padding-top:5px!important; padding-bottom:3px!important; line-height:15px!important"> 
     <div style="font-family:inherit; background:0px center; border-top:0px; border-right:1px solid rgb(222,222,222)!important; border-bottom:0px; border-left:0px; padding:0px 5px; margin:0px; text-align:right!important; height:inherit; font-size:inherit!important; line-height:inherit!important; font-weight:inherit!important; min-width:1.2em!important; color:rgb(170,170,170)!important">
       1 
     </div> 
     <div style="font-family:inherit; background:0px center; border-top:0px; border-right:1px solid rgb(222,222,222)!important; border-bottom:0px; border-left:0px; padding:0px 5px; margin:0px; text-align:right!important; height:inherit; font-size:inherit!important; line-height:inherit!important; font-weight:inherit!important; min-width:1.2em!important; color:rgb(170,170,170)!important">
       2 
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   <td style="padding:0px!important; font-family:Monaco,MonacoRegular,&quot;Courier New&quot;,monospace!important; vertical-align:top!important; border:0px; margin:0px!important; background:0px center; width:774px"> 
    <div style="padding-right:0px; padding-left:0px; margin:0px; white-space:pre; overflow:visible; background:none!important; border:none!important; padding-top:5px!important; padding-bottom:3px!important; line-height:15px!important"> 
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      <span style="font-family:inherit; height:inherit; font-size:inherit!important; line-height:inherit!important; font-weight:inherit!important; color:rgb(0,45,122)!important">targetSdkVersion</span> 
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     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

用较低的 minSdkVersion 来覆盖最大的人群，用最新的 SDK 设置 target 和 compile 来获得最好的外观和行为。

[Picking your compileSdkVersion_ minSdkVersion_ and targetSdkVersion]: https://medium.com/google-developers/picking-your-compilesdkversion-minsdkversion-targetsdkversion-a098a0341ebd#.tz5zzucma
[Support Library]: http://developer.android.com/tools/support-library/index.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog
[lint]: http://developer.android.com/tools/debugging/improving-w-lint.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog
[Link 1]: http://developer.android.com/training/basics/supporting-devices/platforms.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog#version-codes
[Support Library 1]: http://developer.android.com/tools/support-library/features.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog
[Google Play services]: https://developers.google.com/android/guides/overview?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog
[tools_overrideLibrary]: http://tools.android.com/tech-docs/new-build-system/user-guide/manifest-merger?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog#TOC-tools:overrideLibrary-marker
[Android]: http://developer.android.com/about/dashboards/index.html
[VERSION_CODES]: http://developer.android.com/reference/android/os/Build.VERSION_CODES.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog
[API Level]: http://developer.android.com/guide/topics/manifest/uses-sdk-element.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog#ApiLevels
[Android 6.0]: http://developer.android.com/about/versions/marshmallow/android-6.0-changes.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog
[Link 2]: http://android-developers.blogspot.com/2015/08/building-better-apps-with-runtime.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog
[Android 4.4]: http://developer.android.com/about/versions/android-4.4.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog#Behaviors
[set]: http://developer.android.com/reference/android/app/AlarmManager.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog#set%28int,%20long,%20android.app.PendingIntent%29
[setRepeating]: http://developer.android.com/reference/android/app/AlarmManager.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog#setRepeating%28int,%20long,%20long,%20android.app.PendingIntent%29
[menu]: http://android-developers.blogspot.com/2012/01/say-goodbye-to-menu-button.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog
[Gradle]: http://developer.android.com/tools/building/plugin-for-gradle.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog
[Android Studio]: http://developer.android.com/tools/studio/index.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog
[build variant]: http://developer.android.com/tools/building/plugin-for-gradle.html?utm_campaign=adp_series_sdkversion_010616&utm_source=medium&utm_medium=blog#buildVariants