99 lines
5.0 KiB
Plaintext
99 lines
5.0 KiB
Plaintext
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page.title=Zipalign: an Easy Optimization
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@jd:body
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<p>The Android SDK includes a tool called <a
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href="{@docRoot}guide/developing/tools/zipalign.html"><code>zipalign</code></a>
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that optimizes the way an application is packaged. Running zipalign against your
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application enables Android to interact it more efficiently at run time and thus
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has the potential to make it and the overall system run faster. We strongly
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encourage you to use <code>zipalign</code> on both new and already published
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applications and to make the optimized version available — even if your
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application targets a previous version of Android. This article describes how
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<code>zipalign</code> helps performance and how to use it to optimize your
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app.</p>
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<p>In Android, data files stored in each application's apk are accessed by
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multiple processes: the installer reads the manifest to handle the
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permissions associated with that application; the Home application
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reads resources to get the application's name and icon; the system
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server reads resources for a variety of reasons (e.g. to display that
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application's notifications); and last but not least, the resource
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files are obviously used by the application itself.</p>
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<p>The resource-handling code in Android can efficiently access resources when
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they're aligned on 4-byte boundaries by memory-mapping them. But for resources
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that are not aligned (that is, when <code>zipalign</code> hasn't been run on an
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apk), it has to fall back to explicitly reading them — which is slower and
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consumes additional memory.</p>
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<p>For an application developer, this fallback mechanism is very
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convenient. It provides a lot of flexibility by allowing for several
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different development methods, including those that don't include
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aligning resources as part of their normal flow.</p>
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<p>Unfortunately, for users the situation is reversed — reading resources
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from unaligned apks is slow and takes a lot of memory. In the best case, the
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only visible result is that both the Home application and the unaligned
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application launch slower than they otherwise should. In the worst case,
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installing several applications with unaligned resources increases memory
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pressure, thus causing the system to thrash around by having to constantly start
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and kill processes. The user ends up with a slow device with a poor battery
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life.</p>
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<p>Luckily, it's very easy for you to align the resources in your application:</p>
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<ul>
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<li>Using ADT:</li>
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<li style="list-style-type: none; list-style-image: none; list-style-position: outside;">
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<ul>
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<li>The ADT plugin for Eclipse (starting from version 0.9.3) will automatically
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align release application packages if the export wizard is used to create them.
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To use the wizard, right click the project and choose "Android Tools" >
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"Export Signed Application Package..." It can also be accessed from the first
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page of the <code>AndroidManifest.xml</code> editor.</li>
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</ul>
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</li>
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<li>Using Ant:</li><li style="list-style-type: none; list-style-image: none; list-style-position: outside;">
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<ul>
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<li>The <em>Ant</em> build script (starting from Android 1.6) can align
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application packages. Targets for older versions of the Android platform are not
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aligned by the <em>Ant</em> build script and need to be manually aligned.</li>
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<li>Starting from the Android 1.6 SDK, Ant aligns and signs packages automatically,
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when building in debug mode.</li>
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<li>In release mode, Ant aligns packages only if it has enough
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information to sign the packages, since aligning has to happen after signing. In
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order to be able to sign packages, and therefore to align them, <em>Ant</em>
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needs to know the location of the keystore and the name of the key in
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<code>build.properties</code>. The name of the properties are
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<code>key.store</code> and <code>key.alias</code> respectively. If those
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properties are present, the signing tool will prompt to enter the store/key
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passwords during the build, and the script will sign and then align the apk
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file. If the properties are missing, the release package will not be signed, and
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therefore will not get aligned either.</li>
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</ul>
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</li>
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<li>Manually:</li>
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<li style="list-style-type: none; list-style-image: none; list-style-position: outside;">
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<ul>
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<li>In order to manually align a package, <code>zipalign</code>
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is in the <code>tools/</code> folder of Android 1.6 and later SDKs. You can use
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it to align application packages targeting any version of Android. You should run
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it only after signing the apk file, using the following command:
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<br><code>zipalign -v 4 source.apk destination.apk</code></li>
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</ul>
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</li>
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<li>Verifying alignment:</li>
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<li style="list-style-type: none; list-style-image: none; list-style-position: outside;">
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<ul>
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<li>The following command verifies that a package is aligned:<br><code>zipalign -c -v 4 application.apk</code>
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</li>
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</ul>
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</li>
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</ul>
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<p>We encourage you manually run <code>zipalign</code>
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on your currently published applications and to make the newly aligned
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versions available to users. Also, don't forget to align any new
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applications going forward!</p>
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