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page.title=Reduce APK Size
trainingnavtop=true
@jd:body
<div id="tb-wrapper">
<div id="tb">
<h2>This lesson teaches you to</h2>
<ol>
<li><a href="#apk-structure">Understand the APK Structure</a></li>
<li><a href="#reduce-resources">Reduce Resource Count and Size</a></li>
<li><a href="#reduce-code">Reduce Native and Java Code</a></li>
<li><a href="#multiple-apks">Maintain Multiple Lean APKs</a></li>
</ol>
<h2>
You should also read
</h2>
<ul>
<li>
<a href="{@docRoot}studio/build/shrink-code.html">Shrink Your Code and
Resources</a>
</li>
</ul>
</div>
</div>
<p>
Users often avoid downloading apps that seem too large, particularly in
emerging markets where devices connect to often-spotty 2G and
3G networks or work on pay-by-the-byte plans. This article describes how to
reduce your app's APK size, which enables more users to download your app.
</p>
<h2 id="apk-structure">
Understand the APK Structure
</h2>
<p>
Before discussing how to reduce the size of your app, it's helpful to
understand the structure of an app's APK. An APK file consists of a ZIP
archive that contains all the files that comprise your app. These files
include Java class files, resource files, and a file containing compiled
resources.
</p>
<p>
An APK contains the following directories:
</p>
<ul>
<li>{@code META-INF/}: Contains the <code>CERT.SF</code> and
<code>CERT.RSA</code> signature files, as well as the {@code MANIFEST.MF}
manifest file.
</li>
<li>{@code assets/}: Contains the app's assets, which the app can retrieve
using an {@link android.content.res.AssetManager} object.
</li>
<li>
{@code res/}: Contains resources that aren't compiled into
<code>resources.arsc</code>.
</li>
<li>{@code lib/}: Contains the compiled code that is specific to the software
layer of a processor. This directory contains a subdirectory for each
platform type, like <code>armeabi</code>, <code>armeabi-v7a</code>,
<code>arm64-v8a</code>, <code>x86</code>, <code>x86_64</code>, and
<code>mips</code>.
</li>
</ul>
<p>
An APK also contains the following files. Among them,
only <code>AndroidManifest.xml</code> is mandatory.
</p>
<ul>
<li>{@code resources.arsc}: Contains compiled resources. This file contains
the XML content from all configurations of the <code>res/values/</code>
folder. The packaging tool extracts this XML content, compiles it to binary
form, and archives the content. This content includes language strings and
styles, as well as paths to content that is not included directly in the
<code>resources.arsc</code> file, such as layout files and images.
</li>
<li>{@code classes.dex}: Contains the classes compiled in the DEX file format
understood by the Dalvik/ART virtual machine.
</li>
<li>{@code AndroidManifest.xml}: Contains the core Android manifest file.
This file lists the name, version, access rights, and referenced library
files of the app. The file uses Android's binary XML format.
</li>
</ul>
<h2 id="reduce-resources">
Reduce Resource Count and Size
</h2>
<p>
The size of your APK has an impact on how fast your app loads, how much
memory it uses, and how much power it consumes. One of the simple ways to
make your APK smaller is to reduce the number and size of the
resources it contains. In particular, you can remove resources
that your app no longer uses, and you can use scalable {@link
android.graphics.drawable.Drawable} objects in place of image files. This
section discusses these methods as well as several other ways that you can
reduce the resources in your app to decrease the overall size of your APK.
</p>
<h3 id="remove-unused">
Remove Unused Resources
</h3>
<p>
The <a href="{@docRoot}studio/write/lint.html">{@code lint}</a> tool, a
static code analyzer included in Android Studio, detects resources in your
<code>res/</code> folder that your code doesn't reference. When the
<code>lint</code> tool discovers a potentially unused resource in your
project, it prints a message like the following example.
</p>
<pre class="no-pretty-print">
res/layout/preferences.xml: Warning: The resource R.layout.preferences appears
to be unused [UnusedResources]
</pre>
<p class="note">
<strong>Note:</strong> The <code>lint</code> tool doesn't scan the {@code
assets/} folder, assets that are referenced via reflection, or library files
that you've linked to your app. Also, it doesn't remove resources; it only
alerts you to their presence.
</p>
<p>
Libraries that you add to your code may include unused resources. Gradle can
automatically remove resources on your behalf if you enable <a href=
"{@docRoot}studio/build/shrink-code.html">{@code shrinkResources}</a> in
your app's <code>build.gradle</code> file.
</p>
<pre class="prettyprint">
android {
// Other settings
buildTypes {
release {
minifyEnabled true
shrinkResources true
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
</pre>
<p>
To use {@code shrinkResources}, you must enable code shrinking. During the
build process, first <a href=
"{@docRoot}studio/build/shrink-code.html">ProGuard</a> removes unused code
but leaves unused resources. Then Gradle removes the unused resources.
</p>
<p>
For more information about ProGuard and other ways
Android Studio helps you reduce APK size, see <a href=
"{@docRoot}studio/build/shrink-code.html">Shrink Your Code and Resources</a>.
</p>
<p>
In Android Gradle Plugin 0.7 and higher, you can declare the configurations
that your app supports. Gradle passes this information to the build system
using the {@code resConfig} and {@code resConfigs} flavors and the
<code>defaultConfig</code> option. The build system then prevents resources
from other, unsupported configurations from appearing in the APK, reducing
the APK's size. For more information about this feature, see <a href=
"{@docRoot}studio/build/shrink-code.html#unused-alt-resources">Remove unused
alternative resources</a>.
</p>
<h3 id="minimize">
Minimize Resource Use from Libraries
</h3>
<p>
When developing an Android app, you usually use external libraries to improve
your app's usability and versatility. For example, you might reference the
<a href="{@docRoot}topic/libraries/support-library/index.html">Android
Support Library</a> to improve the user experience on older devices, or you
could use <a class="external-link" href=
"https://developers.google.com/android/guides/overview">Google Play
Services</a> to retrieve automatic translations for text within your app.
</p>
<p>
If a library was designed for a server or desktop, it can include many
objects and methods that your app doesn’t need. To include only the parts of
the library that your app needs, you can edit the library's files if the
license allows you to modify the library. You can also use an alternative,
mobile-friendly library to add specific functionality to your app.
</p>
<p class="note">
<strong>Note:</strong> <a href=
"{@docRoot}studio/build/shrink-code.html">ProGuard</a> can clean up some
unnecessary code imported with a library, but it can't remove a library's
large internal dependencies.
</p>
<h3 id="support-densities">
Support Only Specific Densities
</h3>
<p>
Android supports a very large set of devices, encompassing a variety of
screen densities. In Android 4.4 (API level 19) and higher, the framework
supports various densities: <code>ldpi</code>, <code>mdpi</code>,
<code>tvdpi</code>, <code>hdpi,</code> <code>xhdpi</code>,
<code>xxhdpi</code> and <code>xxxhdpi</code>. Although Android supports all
these densities, you don't need to export your rasterized assets to each
density.
</p>
<p>
If you know that only a small percentage of your users have devices with
specific densities, consider whether you need to bundle those densities into
your app. If you don't include resources for a specific screen density,
Android automatically scales existing resources originally designed for other
screen densities.
</p>
<p>
If your app needs only scaled images, you can save even more space by having
a single variant of an image in <code>drawable-nodpi/</code>. We recommend
that every app include at least an <code>xxhdpi</code> image variant.
</p>
<p>
For more information screen densities, see <a class="external-link" href=
"{@docRoot}about/dashboards/index.html#Screens">Screen Sizes and
Densities</a>.
</p>
<h3 id="reduce-frames">
Reduce Animation Frames
</h3>
<p>
Frame-by-frame animations can drastically increase the size of your APK.
Figure 1 shows an example of a frame-by-frame animation separated into
multiple PNG files within a directory. Each image is one frame in the
animation.
</p>
<p>
For each frame that you add to the animation, you increase the number of
images stored in the APK. In Figure 1, the image animates at 30 FPS within
the app. If the image animated at only 15 FPS instead, the animation would
require only half the number of needed frames.
</p>
<figure id="fig-frame-animations">
<img src="{@docRoot}images/training/performance/animation-frames.png" srcset=
"{@docRoot}images/training/performance/animation-frames.png 1x, {@docRoot}images/training/performance/animation-frames_2x.png 2x"
width="803" alt="">
<figcaption>
<strong>Figure 1.</strong> Frame by frame animations stored as resources.
</figcaption>
</figure>
<h3 id="use-drawables">
Use Drawable Objects
</h3>
<p>
Some images don't require a static image resource; the framework can
dynamically draw the image at runtime instead. {@link
android.graphics.drawable.Drawable} objects (<code>&lt;shape&gt;</code> in
XML) can take up a tiny amount of space in your APK. In addition, XML {@link
android.graphics.drawable.Drawable} objects produce monochromatic images
compliant with material design guidelines.
</p>
<h3 id="reuse-resources">
Reuse Resources
</h3>
<p>
You can include a separate resource for variations of an image, such as
tinted, shaded, or rotated versions of the same image. We recommend, however,
that you reuse the same set of resources, customizing them as needed at
runtime.
</p>
<p>
Android provides several utilities to change the color of an asset, either
using the {@code android:tint} and {@code tintMode} attributes on Android 5.0
(API level 21) and higher. For lower versions of the platform, use the {@link
android.graphics.ColorFilter} class.
</p>
<p>
You can also omit resources that are only a rotated equivalent of another
resource. The following code snippet provides an example of turning an
"expand" arrow into a "collapse" arrow icon by simply rotating the original
image 180 degrees:
</p>
<pre class="prettyprint">
&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;rotate xmlns:android="http://schemas.android.com/apk/res/android"
android:drawable="@drawable/ic_arrow_expand"
android:fromDegrees="180"
android:pivotX="50%"
android:pivotY="50%"
android:toDegrees="180" /&gt;
</pre>
<h3 id="render-code">
Render From Code
</h3>
<p>
You can also reduce your APK size by procedurally rendering your images.
Procedural rendering frees up space because you no longer store an image file
in your APK.
</p>
<h3 id="crunch">
Crunch PNG Files
</h3>
<p>
The <code>aapt</code> tool can optimize the image resources placed in
<code>res/drawable/</code> with lossless compression during the build
process. For example, the <code>aapt</code> tool can convert a true-color PNG
that does not require more than 256 colors to an 8-bit PNG with a color
palette. Doing so results in an image of equal quality but a smaller memory
footprint.
</p>
<p>
Keep in mind that the <code>aapt</code> has the following limitations:
</p>
<ul>
<li>The <code>aapt</code> tool does not shrink PNG files contained in the
<code>asset/</code> folder.
</li>
<li>Image files need to use 256 or fewer colors for the <code>aapt</code>
tool to optimize them.
</li>
<li>The <code>aapt</code> tool may inflate PNG files that have already been
compressed. To prevent this, you can use the <code>cruncherEnabled</code>
flag in Gradle to disable this process for PNG files:
</li>
</ul>
<pre class="prettyprint">
aaptOptions {
cruncherEnabled = false
}
</pre>
<h3 id="compress">
Compress PNG and JPEG Files
</h3>
<p>
You can reduce PNG file sizes without losing image quality using tools like
<a class="external-link" href=
"http://pmt.sourceforge.net/pngcrush/">pngcrush</a>, <a class="external-link"
href="https://pngquant.org/">pngquant</a>, or <a class="external-link" href=
"https://github.com/google/zopfli">zopflipng</a>. All of these tools can
reduce PNG file size while preserving image quality.
</p>
<p>
The {@code pngcrush} tool is particularly effective: This tool iterates over
PNG filters and zlib (Deflate) parameters, using each combination of filters
and parameters to compress the image. It then chooses the configuration that
yields the smallest compressed output.
</p>
<p>
For JPEG files, you can use tools like <a class="external-link" href=
"http://www.elektronik.htw-aalen.de/packjpg/">packJPG</a> that compress JPEG
files into a more compact form.
</p>
<h3 id="use-webp">
Use WebP File Format
</h3>
<p>
Instead of using PNG or JPEG files, you can also use the <a class=
"external-link" href="https://developers.google.com/speed/webp/">WebP</a>
file format for your images. The WebP format provides lossy compression (like
JPEG) as well as transparency (like PNG) but can provide better compression
than either JPEG or PNG.
</p>
<p>
Using the WebP file format has a few notable drawbacks, however. First,
support for WebP is not available in versions of the platform lower than
Android 3.2 (API level 13). Second, it takes a longer amount of time for the
system to decode WebP than PNG files.
</p>
<p class="note">
<strong>Note:</strong> Google Play accepts APKs only if the included icons
use the PNG format. You can't use other file formats like JPEG or WebP for
app icons if you intend to publish your app through Google Play.
</p>
<h3 id="vector">
Use Vector Graphics
</h3>
<p>
You can use vector graphics to create resolution-independent icons and other
scalable media. Using these graphics can greatly reduce your APK footprint.
Vector images are represented in Android as {@link
android.graphics.drawable.VectorDrawable} objects. With a {@link
android.graphics.drawable.VectorDrawable } object, a 100-byte file can
generate a sharp image the size of the screen.
</p>
<p>
However, it takes a significant amount of time for the system to render each
{@link android.graphics.drawable.VectorDrawable} object, and larger images
take even longer to appear on the screen. Therefore, consider using these
vector graphics only when displaying small images.
</p>
<p>
For more information on working with {@link
android.graphics.drawable.VectorDrawable } objects, see <a class=
"external-link" href="{@docRoot}training/material/drawables.html">Working
with Drawables</a>.
</p>
<h2 id="reduce-code">
Reduce Native and Java Code
</h2>
<p>
There are several methods you can use to reduce the size of the Java and
native codebase in your app.
</p>
<h3 id="remove-generated">
Remove Unnecessary Generated Code
</h3>
<p>
Make sure to understand the footprint of any code which is automatically
generated. For example, many protocol buffer tools generate an excessive
number of methods and classes, which can double or triple the size of your
app.
</p>
<h3 id="remove-enums">
Remove Enumerations
</h3>
<p>
A single enum can add about 1.0 to 1.4 KB of size to your app's
<code>classes.dex</code> file. These additions can quickly accumulate for
complex systems or shared libraries. If possible, consider using the
<code>@IntDef</code> annotation and <a href=
"{@docRoot}studio/build/shrink-code.html">ProGuard</a> to strip enumerations
out and convert them to integers. This type conversion preserves all of the
type safety benefits of enums.
</p>
<h3 id="reduce-binaries">
Reduce the Size of Native Binaries
</h3>
<p>
If your app uses native code and the Android NDK, you can also reduce the
size of your app by optimizing your code. Two useful techniques are
removing debug symbols and not extracting native libraries.
</p>
<h4 id="remove-debug">
Remove Debug Symbols
</h4>
<p>
Using debug symbols makes sense if your application is in development and
still requires debugging. Use the <code>arm-eabi-strip</code> tool, provided
in the Android NDK, to remove unnecessary debug symbols from native
libraries. After that, you can compile your release build.
</p>
<h4 id="extract-false">
Avoid Extracting Native Libraries
</h4>
<p>
Store {@code .so} files uncompressed in the APK, and set the {@code
android:extractNativeLibs} flag to false in the <a href=
"{@docRoot}guide/topics/manifest/application-element.html">{@code
<application>}</a> element of your app manifest. This will prevent
{@link android.content.pm.PackageManager} from copying out {@code .so} files
from the APK to the filesystem during installation and will have the added
benefit of making delta updates of your app smaller.
</p>
<h2 id="multiple-apks">
Maintain Multiple Lean APKs
</h2>
<p>
Your APK can contain content that users download but never use, like regional
or language information. To create a minimal download for your users, you can
segment your app into several APKs, differentiated by factors such as screen
size or GPU texture support.
</p>
<p>
When a user downloads your app, their device receives the correct APK based
on the device's features and settings. This way, devices don't receive assets
for features that the devices don't have. For example, if a user has a
<code>hdpi</code> device, they don’t need <code>xxxhdpi</code> resources that
you might include for devices with higher density displays.
</p>
<p>
For more information, see <a href=
"{@docRoot}studio/build/configure-apk-splits.html">Configure APK Splits</a>
and <a class="external-link" href=
"{@docRoot}training/multiple-apks/index.html">Maintaining Multiple APKs</a>.
</p>