When you are browsing the Google Play store for new apps, or reading websites that review Android apps, you will eventually stumble upon the term Holo. Chance is, this will happen frequently. Sometimes, applications have Holo added to their name, at other times, it is listed in the description of the app or as one of its features.
Holo, or Holo theme, is a standard theme for Android apps that Google first introduced with Android 3.0 Honeycomb. The company requires manufacturers to include the unmodified Holo theme in Android 4.0 or higher devices if they want to integrate Android Market on their device. Manufacturers can still ship their devices with their own custom themes to provide users with a unified experience across all devices by that manufacturer.
As far as Holo is concerned it is fair to say that the majority of Android 4.0 or higher devices have the themes built-in so that apps can make use of their resources. The basic idea behind Holo was to reduce (virtually eliminate) the design variance in regards to system themes.
If you are a developer, you have noticed that you do have access to three different Holo themes: Holo Light, Holo Dark and Holo Light with dark action bars. Here are three screenshots that showcase how these themes look like and differ from one another.
If you compare the Holo design to the design of previous Android apps you will notice that it has come a long way since then. Developers can still create their own visual designs so that their apps do not need to look like the apps displayed here at all.
That does not mean that devices running a lower version than Android 3.0 cannot benefit from Holo designed apps as well. Designers can use the resources and styles, or use something like Holo Everywhere instead.
Information about the implementation of themes are available in this introductory blog post at the official Android Developers blog. It addresses several common issues like how developers can use Holo but still support older Android (2.x) systems as well. Additional information are available at the official Styles and Themes guide.Advertisement
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