This article was requested by some of our community members. It is based on the Android Gallery, ImageView Example tutorial by Sasikumar (Part 1 is here). I extended his example with a new function. If you long click on the big image, an alert dialog show up and ask “Do you want to use this image as a wallpaper?". If you click yes, the actually image will be your new wallpaper.

I only changed the Activity class:

First of all, define what do we mean under "speed": in one hand its the time that the code needs to execute, on the other hand its the time the user needs to wait for the user interface. The two things can greatly differ, of course you must optimize the code performance, but the most important is what the user sees from it. Don't make the user wait, unless its necessary.

Do not pull back the ui thread
The very basic principle is to never run slow operations on the user interface thread! If you do this the interface will freeze until the operation is executed, which is not a nice user experience. If the execution takes too long the android system will detect it and offer the opportunity to the user to force close the frozen application:

So in this tutorial I'm going to show you how to refresh imageviews' contents periodically (let say by Handlers if you download the picture from web). I had painful 2 days figuring out what's a good solution here, I tried to give IDs to imageviews and that sort of sick things, but believe me, it wasn't worth it. The solution is so simply that I hardly can believe. What we're lookign for here is instead of create new Adapters and HashMaps (which contains ListView data), we just update it's values, and Android will do the trick for us. The most important thing is DO NOT AT ANY CIRCUMSTANCES CREATE A NEW ADAPTER (or a new data source that holds the Adapter's data). There's an exception of course, you obviously have to create a new Adapter in OnCreate() { }.

Let me show you how it works:

Pretty easy! :)
Use the context’s setWallpaper method.

Don’t forget to add the SET_WALLPAPER permission to your AndroidManifest.xml!

Differences between api versions
On Android 1.5 the wallpaper looks cool, doesn’t it? :) The backgroud fills the screen.

But on 1.6 and higher android strechs the wallpaper like this:

It’s not bad if you use high resolution wallpaper, but the low res wallpapers look crappy.

One of the strange things with android is that there is no "the user has closed the application" event. Applications activities often just go to the background, and the android system may kill them whenever it wants, even when another activity of the application is still running in the foreground.

You can not be sure that activities you started and sent to the background are sill there storing their state, and if you are just an android user, you can not be sure that applications that you left simply by pressing back button are completely destroyed.

To make it more complex, using intents it is even possible to start an activity of another application.

Using web services on android phones, is pretty simple. For most popular services, there is a usable library available.
Here is a little snippet for using an android library, called android-xmlrpc.

To enable your application to initiate a phone call, you must set permissions in the manifest file:

Now create a new activity with a call method. It should look like this: