What are best practices for using SVG icons on Android?

I am about to create my first Android native (so not browser based) app and looking for some good practices regarding icon creating/provisioning. Since it should support multiple devices/resolutions I thought it is best to use SVG to create them. There is at least this lib: http://code.google.com/p/svg-android/ that promises to offer support for SVG on Android.

So far, I have not found resources describing the usage of this or another library as a means to render SVG Icons on the device, so I am a bit reluctant in using it. The best I have seen so far is using SVG as the source format for pre-rendering png based icons in different resolutions.

So my questions is: Are SVG icons a good option to use directly on the device without a png pre-rendering step (does it work at all), and if, why does nobody seem to use this approach?

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最佳答案

For Android older than Lollipop, your best practice for SVG on Android is going to be to use a tool to convert your SVG to PNG at the size(s) you're interested in. Existing SVG support for Android is not comprehensive of what you're likely to find in an SVG file, and even if it were, the support is not built into the OS so using them directly for icons is definitely out.

Beginning with Lollipop (API 21) see What are best practices for using SVG icons on Android?. Thanks to @MarkWhitaker @AustynMahoney for pointing this out.

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SVG icons are not a good option to use directly on a device if they need to be scaled to many different sizes, which is usually why you'd want to use vector format in the first place. A large icon will never scale down gracefully because, well, computer displays are made out of pixels. So the lines of the vector image may get aligned "in between pixels", creating a blurry border. Moreover, large icons need more details than small icons, which need very few details. A detailed icon does not look good in very small size, and a simple icon does not look good when scaled into very large size. I recently read an excellent article on this by a professional UI designer: About those vector icons.

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This is what we are using to transform a SVG file into multiple resolutions. For example, to generate the launch icon: svg2png -w48 icon.svg

#!/bin/bash -e
# Transforms a SVG into a PNG for each platform
# Sizes extracted from
# http://developer.android.com/design/style/iconography.html


[ -z $2 ] && echo -e "ERROR: filename and one dimension (-w or -h) is required, for example:\nsvg2png -w48 icon.svg\n" && exit 1;
FILENAME=$2
DEST_FILENAME=`echo $2 | sed s/\.svg/\.png/`
FLAG=`echo $1 | cut -c1-2`
ORIGINAL_VALUE=`echo $1 | cut -c3-`


if [ "$FLAG" != "-w" ] && [ "$FLAG" != "-h" ]; then
echo "Unknown parameter: $FLAG"
exit 1
fi


# PARAMETERS: {multiplier} {destination folder}
function export {
VALUE=$(echo "scale=0; $ORIGINAL_VALUE*$1" | bc -l)
CMD="inkscape $FLAG$VALUE --export-background-opacity=0 --export-png=src/main/res/$2/$DEST_FILENAME src/main/svg/$FILENAME > /dev/null"
echo $CMD
eval $CMD
}


export 1 drawable-mdpi
export 1.5 drawable-hdpi
export 2 drawable-xhdpi
export 3 drawable-xxhdpi
export 4 drawable-xxxhdpi
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I've just posted a script for generating all the platform icons for PhoneGap apps that may be of value. Yet to add code for generating screens.

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Another option is to convert your SVG assets into TTF font type. Include the font on your app and use it that way. This does the trick for monochromatic simple shapes.

There are several free conversion tools.

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Since nacho-coloma's answer helped me, I've taken his excellent script and made it slightly easier to use on a daily basis.

First:

  1. Create directory drawable-svg next to your res directory.
  2. Place your svg files and this script in drawable-svg.
  3. Make the script executable.
  4. Run it. In Ubuntu you can simply double-click it in Nautilus and make it run in a terminal.

And later when you get new svg files:

  1. Place new svg files in drawable-svg and run the script again.

By default it will do what you want: Scale every svg file into png files and put them into ../res/drawable-mdpi, ../res/drawable-hdpi etc.

The script takes two parameters:

  1. The svg file pattern to scale, default: *.svg
  2. The base directory for put, default ../res/ (i.e. your res directory with the above mentioned setup).

You can experiment by scaling a single svg into pngs in the current directory like this:

$ ./svg2png test.svg .

Or simply process all images:

$ ./svg2png

I guess you could place the drawable-svg inside the res directory, but I haven't looked into what gets wrapped up in the final APK. Also, my svg files have - in their names, which Android doesn't like, and my script takes care of renaming the png files to something valid on Android.

I'm using ImageMagick for the conversion which is slightly more standard that Inkscape (though I liked the approach). Both methods are included in the script for reference.

Here's the script:

#!/bin/bash


scalesvg ()
{
svgfile="$1"
pngdir="$2"
pngscale="$3"
qualifier="$4"


svgwidthxheight=$(identify "$svgfile" | cut -d ' ' -f 3)
svgwidth=${svgwidthxheight%x*}
svgheight=${svgwidthxheight#*x}


pngfile="$(basename $svgfile)" # Strip path.
pngfile="${pngfile/.svg/.png}" # Replace extension.
pngfile="${pngfile/[^A-Za-z0-9._]/_}" # Replace invalid characters.
pngfile="$pngdir/$qualifier/$pngfile" # Prepend output path.


if [ ! -d $(dirname "$pngfile") ]; then
echo "WARNING: Output directory does not exist: $(dirname "$pngfile")"
#echo "Exiting"
#exit 1
echo "Outputting here instead: $pngfile"
pngfile="$qualifier-${svgfile/.svg/.png}"
fi


pngwidth=$(echo "scale=0; $svgwidth*$pngscale" | bc -l)
pngheight=$(echo "scale=0; $svgheight*$pngscale" | bc -l)
pngdensity=$(echo "scale=0; 72*$pngscale" | bc -l) # 72 is default,


echo "$svgfile ${svgwidth}×${svgheight}px -> $pngfile ${pngwidth}×${pngheight}px @ $pngdensity dpi"


convert -background transparent -density $pngdensity "$svgfile" "$pngfile"
#inkscape -w${pngwidth} --export-background-opacity=0 --export-png="$pngfile" "$svgfile" > /dev/null
#convert "$svgfile" -background transparent -scale ${pngwidth}x${pngheight} "$pngfile"
}






svgfiles="$1"
svgfiles="${svgfiles:=*.svg}" # Default to input all *.svg in current dir.


pngdir="$2"
pngdir="${pngdir:=../res}" # Default to place output pngs to ../res, ie. ../res/drawable-hdpi etc.


for svgfile in $svgfiles; do
echo "Scaling $svgfile ..."
scalesvg "$svgfile" "$pngdir" 0.75 drawable-ldpi
scalesvg "$svgfile" "$pngdir" 1    drawable-mdpi
scalesvg "$svgfile" "$pngdir" 1.5  drawable-hdpi
scalesvg "$svgfile" "$pngdir" 2    drawable-xhdpi
scalesvg "$svgfile" "$pngdir" 3    drawable-xxhdpi
scalesvg "$svgfile" "$pngdir" 4    drawable-xxxhdpi
done


echo -n "Done."
read # I've made it wait for Enter -- convenient when run from Nautilus.
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From Lollipop (API 21) onwards, Android defines the VectorDrawable class, for defining drawables based on vector graphics. Android Studio 1.4 adds the "Vector Asset Studio" to make them easier to work with, including an SVG import feature and a new Gradle plugin that generates PNG versions of VectorDrawable icons at build time for API 20 and earlier. There's also a third-party tool for converting SVGs to VectorDrawables. Bear in mind that although vector drawables can be defined in XML, the file format is not SVG and not all SVG files can be successfully converted. Simple graphics like icons should work OK.

If you still need to generate PNGs yourself, you'll need to generate your icons at various resolutions. For ease of generating those PNGs I design icons as SVG and then export to the various sizes using Inkscape which is free and cross-platform. It's got some nice features for designing icons, including the Icon Preview view (see below), and it generates nice crisp PNGs.

enter image description here

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I've just started using Victor, an open source library by Trello, to convert SVG files to PNG files of the various required resolutions during build time.

PROS

  • You won't have to run a script or tool to create various PNG files every time you change or add an icon. (You do need to hit Rebuild in Android Studio when you've added a new svg file or renamed an existing one)
  • No PNG's in your source, so there's less clutter.

CONS

  • The only downside I've seen so far is that Android Studio doesn't yet recognize generated resources in XML, so you'll get some red warnings in your XML files and you don't have autocomplete for your SVG based drawables. It builds fine though, and this issue should be fixed in a future version of Android Studio.

If you use SVG generated by http://materialdesignicons.com/ be sure to either download the whole file, or copy from the 'SVG File'-tab when choosing 'View SVG'

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I've never had much luck running Linux shell scripts in Cygwin on Windows. So here is a batch file that does what Nacho Coloma's bash script does. One small difference, is that this batch file requires both an input and an output file name, as in "svg2png -w24 input.svg output.png".

Set up an "svg" folder in your project's src/main directory and copy your SVG files and this batch file to that folder, per Stephan's instructions. Run the batch file from the svg folder. If you're on 32-bit Windows, then you will likely need to change the path to Inkscape to use "Program Files (x86)".

@echo off
echo Convert an SVG file to a PNG resource file with multiple resolutions.


rem Check the arguments
set temp=%1
set switch=%temp:~0,2%
set pixels=%temp:~2%
if not "%switch%"=="-w" (
if not "%switch%"=="-h" (
echo Error:  Invalid image width or height switch.  Use -w or -h, with target image size in dp appended.
goto :error
))
echo %pixels%| findstr /r /c:"^[1-9][0-9]*$" >nul
if errorlevel 1 (
echo Error:  Invalid numeric image size.  Image size must be a positive integer.
goto :error
)
if "%3"=="" (
echo Error:  Not enough arguments.
goto :error
)
if not "%4"=="" (
echo Error:  Too many arguments.
goto :error
)


call :export %1 %2 %3 mdpi
call :export %1 %2 %3 hdpi
call :export %1 %2 %3 xhdpi
call :export %1 %2 %3 xxhdpi
call :export %1 %2 %3 xxxhdpi
exit /b


:export
rem parameters: <width/height> <input-file> <output-file> <density>


set temp=%1
set switch=%temp:~0,2%
set pixels=%temp:~2%


if %4==mdpi set /a size=%pixels%
if %4==hdpi set /a size=%pixels%*3/2
if %4==xhdpi set /a size=%pixels%*2
if %4==xxhdpi set /a size=%pixels%*3
if %4==xxxhdpi set /a size=%pixels%*4


echo %size% pixels ../res/drawable-%4/%3
"C:\Program Files\Inkscape\inkscape.exe" %switch%%size% --export-background-opacity=0 --export-png=../res/drawable-%4/%3 %2
exit /b


:error
echo Synopsis: svg2png -w^<width-pixels^>^|-h^<height-pixels^> ^<input-file^> ^<output-file^>
echo Example:  svg2png -w24 "wifi white.svg" wifi_connect_24dp.png
exit /b
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svg is awesome. who want use svg:

right click on drawable "new/Vector Asset" choose "material icon" for default icons and "locale SVG file" for your file in your computer hard drive and in "resource name" type name for svg file then click on "next" button and "finish"

and you can use that in drawable. fillcolor must be hard code.

simple example

navigation_toggle.xml

<vector xmlns:android="http://schemas.android.com/apk/res/android"
android:width="24dp"
android:height="24dp"
android:viewportWidth="24.0"
android:viewportHeight="24.0">
<path
android:fillColor="#FFFFFF"
android:pathData="M3,18h18v-2H3v2zm0,-5h18v-2H3v2zm0,-7v2h18V6H3z"/>
</vector>
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Android Support Library 23.2 Support Vector Drawables and Animated Vector Drawables

  1. add vectorDrawables.useSupportLibrary = true to your build.gradle file.
  2. Use app:srcCompat="@drawable/ic_add" instead of android:src="..." or setImageResource() for your ImageView

http://android-developers.blogspot.sk/2016/02/android-support-library-232.html

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Good news everyone! Since android support library 23.2 we can use svg-s till back to API level 7!

If you wanna be compatible backwards only till Lollipop (API 21) check Mark Whitaker's answer, but if you want to go below you need to add these lines to your build.gradle: 

// Gradle Plugin 2.0+ (if you using older version check the library announcement link)
android {
defaultConfig {
vectorDrawables.useSupportLibrary = true
}
}

Also keep in mind that:

  • instead of android:src you need to use the app:srcCompat attribute in ImageViews.
  • you cannot use svg-s in StateListDrawables or other xml drawables, create them programmatically instead.
  • you cannot use the android:background attribute or View.setBackgroundResource() function, use the View.setBackground() instead.
  • you cannot use svg-s in case of Notifications.

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