I have recently spent some time getting all the appropriate drawable assets together for the notifications in an app, including support of Lollipop, Wear, and pre-Lollipop devices. Unfortunately, it took a lot of digging and a bit of trial and error to get everything right, so I figured I would document everything in one place in the hopes that it helps someone else (or, maybe it helps me next time I’m trying to remember how I did all this).
TL; DR
| DEVICES | SIZE | PADDING | COLOR(S) | DENSITY | |
|---|---|---|---|---|---|
| SMALL ICON | phone, tablet | 24×24 dp | 1 dp | #ffffff, transparent | any |
| ACTION ICON | phone, tablet | 32×32 dp | 4 dp | #ffffff, transparent | any |
| ACTION ICON | wear | 64×64 dp | 8 dp | #ffffff, transparent | hdpi |
| BACKGROUND | wear | 400×400 px or 600×400 px | any | any | nodpi |
Small Icon
The small icon is in the lower right corner of a notification on Ice Cream Sandwich through KitKat and gets put inside a circle and brought over to the left on Lollipop. One version of the icon will be equally suited for use on all of those platform versions. The icon should be 24×24 dp with about 1 dp of padding on each side. It should be pure white (#ffffff) on a transparent background only, using the alpha channel as needed for blending. Provide as many different densities (e.g. xhdpi, xxhdpi, etc.) as needed.
Action Icon
Action icons are used with any actions that you may add to your notification, for example the Delete or Archive button that GMail adds to a new message notification. These icons should follow the Action Bar icon sizing parameters: 32×32 dp with 4 dp of padding on each side. These should also be only pure white (#ffffff) on a transparent background, using the alpha channel as needed for blending. These icons will be automatically re-colored on Lollipop devices, no additional assets required. Provide as many different densities (e.g. xhdpi, xxhdpi, etc.) as needed.
For Wear, you will want alternative versions of your action icons or you will end up with your icons being scaled up significantly and looking blurry on Wear devices. The Wear versions should be double the size of the phone and tablet version: 64×64 dp. However, currently you only need to provide hdpi versions for Wear. So, ultimately, you just need an hdpi asset that is 96×96 px. You must also name these Wear versions differently so that they do not collide with your phone/tablet version.
Background
The Background is used only for Wear devices. It should be 400×400 px or 640×400 px, density independent. It can be full color. A 640×400 version will parallax more than a 400×400 version, which may not parallax at all, depending on the device being used. Since they are density independent, these assets should be placed in your drawable-nodpi directory.
Scott Weber 