Android – Live Wallpaper part 2

March 22nd, 2012 by Paul Gregoire

Let’s make the star that we created in part 1 rotate in just a few simple steps. Although before we start, I’d like to note that we are technically rotating the entire canvas and not just the star itself; adding more than one star to the display will clearly expose this minor detail. I’ve done some research on the rotation of multiple individual items at-once, but I have not yet found a solution that fits; feel free to comment if you are aware of how to accomplish it.

The code modifications below are being in the LiveWallpaper.java source file, we are not using the only other source file GoldstarActivity.java at this time.

1. Add a variable where we keep track of the first frame drawn. This will prevent some calculations from being executed more than once per instance.

2. To rotate the star, we will use degrees. In steps 2 and 3, two methods of generation are shown. In this section we use a float counter for degrees of rotation.

3. In this section we use a fixed array for degrees of rotation. To do so, we also must create an index counter and an array of 360 floats; again, its up-to-you as to which option to use.

4. If using the array method, the onCreate method is modified to pre-fill our array when the application is first initialized.

Note: I’ve tried both methods for degree cycling and they seem equally fast on my device.

4. Modify our drawing code from part 1. The code block is here for reference.

Before

After (using float counter)

After (using float array)

6. As an aside to what we done thus far, you can easily add another star with a couple extra lines like so:

The additional star will be down and to the right of the primary star. This star will not rotate per-se but instead will “orbit” the primary star.

7. Last step, build and run in the emulator. Right click on the goldstar project in Package Explorer and select Run As -> Android Application. If you haven’t created any AVD (virtual devices), you’ll be prompted to create one. Creation of an AVD is covered here.

When everything works, you’ll see this in the Eclipse console:

I recorded the emulator running the apk in this screencast

Running on my Galaxy Nexus

In the sample code, I’ve refactored the original class alittle to make things more clear.
Project Source

End of part two.

, , , ,

Android – Live Wallpaper

March 17th, 2012 by Paul Gregoire

Herein I shall walk you through the steps for creating a live wallpaper in Android. Before we begin any Android development, the SDK and ADT plugin for Eclipse will need to be installed. The best installation guide is here; Disregard this if you already have the SDK and plugin installed. For this first part, we will simply display a graphic and in the followups we will do some animation. Without further ado, let’s get started.

1. The first step, is to create the new project
File -> New -> Android Project

We will call it “goldstar” and target Android 2.1 (API 7); this version of Android was the first to support Live Wallpapers.

2. Open up the AndroidManifest.xml file and add the nodes that we will need to support our application. Here is the manifest before our additions were
made:

This is the “after” version, where we added our feature, permission, and service nodes:

3. Create a metadata file for our service. This is accomplished by making an xml directory within the res folder of the project. Create a new file named “metadata.xml” in this folder with these contents:

4. Add a description for our application. Open the strings.xml file and add a string with a name of “wallpaper_description” and a value of “Goldstar Live”. You may actually use whatever value suits you, this one is just for the example.

5. Get the svg library and place it in the “libs” folder; this folder must be created manually, if it does not already exist in the project.
We are using svg-android library from http://code.google.com/p/svg-android/ for this example. This library was also used in the popular “Androidify” application.

6. Locate an SVG image file to use in our application, preferrably one that is not copyrighted. Remember that google is your friend

https://www.google.com/search?q=star%20svg&orq=star+filetype:+svg

Here’s a gold star on wikimedia that you can use: https://upload.wikimedia.org/wikipedia/commons/9/9c/Golden_star.svg

Once you have a suitable file, save it into the “raw” directory within the “res” directory of the project. Note that your resource may only contain this range of characters in its name: a-z0-9_.

7. Now for some code; create a new class in the wallpaper package and name it LiveWallpaper. Set the super class to android.service.wallpaper.WallpaperService and click Finish. Your new class should appear like this:

8. Create an internal class named StarEngine which extends Engine. The result of this should appear like so:

9. Right-click on StarEngine and select “Source -> Override/Implement Methods”. Now select the following methods:

onCreate
onDestroy
onVisibilityChanged
onSurfaceChanged

then click ok. This will create the method stubs that we are interested in.

10. Modify the onCreateEngine method to create a new instance of our engine.

We have also added to static variables for the frame rate and scene width.

11. Load our svg asset. Create a local engine variable and modify the onCreate method like so:

This will read the file resource and parse it to create an SVG image object.

12. Thread and handler must now be setup to take care of drawing on the canvas. We modify the engine like so:

13. Drawing on the canvas. In our drawFrame method we will use our svg asset and draw it into view.

14. Build and run in the emulator; you should see something like this:

15. Lastly, if you want to have nicer launcher images for your application there are free services to utilize such as this one:

http://android-ui-utils.googlecode.com/hg/asset-studio/dist/icons-launcher.html

Just upload your image and do a little configuration and you get a zip containing all the launcher images you need.

Project Source

End of part one; for part two we will cover animation.

, , ,