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diff --git a/docs/html/resources/articles/zipalign.jd b/docs/html/resources/articles/zipalign.jd new file mode 100644 index 0000000..013d0fe --- /dev/null +++ b/docs/html/resources/articles/zipalign.jd @@ -0,0 +1,98 @@ +page.title=Zipalign: an Easy Optimization +@jd:body + +<p>The Android SDK includes a tool called <a +href="{@docRoot}guide/developing/tools/zipalign.html"><code>zipalign</code></a> +that optimizes the way an application is packaged. Running zipalign against your +application enables Android to interact it more efficiently at run time and thus +has the potential to make it and the overall system run faster. We strongly +encourage you to use <code>zipalign</code> on both new and already published +applications and to make the optimized version available — even if your +application targets a previous version of Android. This article describes how +<code>zipalign</code> helps performance and how to use it to optimize your +app.</p> + +<p>In Android, data files stored in each application's apk are accessed by +multiple processes: the installer reads the manifest to handle the +permissions associated with that application; the Home application +reads resources to get the application's name and icon; the system +server reads resources for a variety of reasons (e.g. to display that +application's notifications); and last but not least, the resource +files are obviously used by the application itself.</p> + +<p>The resource-handling code in Android can efficiently access resources when +they're aligned on 4-byte boundaries by memory-mapping them. But for resources +that are not aligned (that is, when <code>zipalign</code> hasn't been run on an +apk), it has to fall back to explicitly reading them — which is slower and +consumes additional memory.</p> + +<p>For an application developer, this fallback mechanism is very +convenient. It provides a lot of flexibility by allowing for several +different development methods, including those that don't include +aligning resources as part of their normal flow.</p> + +<p>Unfortunately, for users the situation is reversed — reading resources +from unaligned apks is slow and takes a lot of memory. In the best case, the +only visible result is that both the Home application and the unaligned +application launch slower than they otherwise should. In the worst case, +installing several applications with unaligned resources increases memory +pressure, thus causing the system to thrash around by having to constantly start +and kill processes. The user ends up with a slow device with a poor battery +life.</p> + +<p>Luckily, it's very easy for you to align the resources in your application:</p> + +<ul> +<li>Using ADT:</li> +<li style="list-style-type: none; list-style-image: none; list-style-position: outside;"> +<ul> +<li>The ADT plugin for Eclipse (starting from version 0.9.3) will automatically +align release application packages if the export wizard is used to create them. +To use the wizard, right click the project and choose "Android Tools" > +"Export Signed Application Package..." It can also be accessed from the first +page of the <code>AndroidManifest.xml</code> editor.</li> +</ul> +</li> +<li>Using Ant:</li><li style="list-style-type: none; list-style-image: none; list-style-position: outside;"> + +<ul> +<li>The <em>Ant</em> build script (starting from Android 1.6) can align +application packages. Targets for older versions of the Android platform are not +aligned by the <em>Ant</em> build script and need to be manually aligned.</li> +<li>Starting from the Android 1.6 SDK, Ant aligns and signs packages automatically, +when building in debug mode.</li> +<li>In release mode, Ant aligns packages only if it has enough +information to sign the packages, since aligning has to happen after signing. In +order to be able to sign packages, and therefore to align them, <em>Ant</em> +needs to know the location of the keystore and the name of the key in +<code>build.properties</code>. The name of the properties are +<code>key.store</code> and <code>key.alias</code> respectively. If those +properties are present, the signing tool will prompt to enter the store/key +passwords during the build, and the script will sign and then align the apk +file. If the properties are missing, the release package will not be signed, and +therefore will not get aligned either.</li> +</ul> +</li> +<li>Manually:</li> +<li style="list-style-type: none; list-style-image: none; list-style-position: outside;"> +<ul> +<li>In order to manually align a package, <code>zipalign</code> +is in the <code>tools/</code> folder of Android 1.6 and later SDKs. You can use +it to align application packages targeting any version of Android. You should run +it only after signing the apk file, using the following command: +<br><code>zipalign -v 4 source.apk destination.apk</code></li> +</ul> +</li> +<li>Verifying alignment:</li> +<li style="list-style-type: none; list-style-image: none; list-style-position: outside;"> +<ul> +<li>The following command verifies that a package is aligned:<br><code>zipalign -c -v 4 application.apk</code> +</li> +</ul> +</li> +</ul> + +<p>We encourage you manually run <code>zipalign</code> +on your currently published applications and to make the newly aligned +versions available to users. Also, don't forget to align any new +applications going forward!</p> |