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Android 4.2: Jelly Bean

Android 4.2: A new flavor of Jelly Bean.

Android 4.2 takes the speed and simplicity of Jelly Bean to a different level – a completely new camera experience that’s beyond smart, a new form of typing that helps you power through your messages, and much more.

Android 4.2 (JELLY_BEAN_MR1) is an update to the Jelly Bean release that offers new features for users and app developers. This document provides an introduction to the most notable and useful new APIs for developers.
As an app developer, you should download the Android 4.2 system image and SDK platform from the SDK Manager as soon as possible. If you don’t have a device running Android 4.2 on which to test your app, use the Android 4.2 system image to test your app on the Android emulator. Then build your apps against the Android 4.2 platform to begin using the latest APIs.


 Daydream is a new interactive screensaver mode for Android devices. It activates automatically when the device is inserted into a dock or when the device is left idle while plugged in to a charger (instead of turning the screen off). Daydream displays one dream at a time, which may be a purely visual, passive display that dismisses upon touch, or may be interactive and responsive to the full suite of input events. Your dreams run in your app’s process and have full access to the Android UI toolkit, including views, layouts, and animations, so they are more flexible and powerful than either live wallpapers or app widgets.

Secondary Displays

Android now allows your app to display unique content on additional screens that are connected to the user’s device over either a wired connection or Wi-Fi. To create unique content for a secondary display, extend the Presentation class and implement the onCreate() callback. Within onCreate(), specify your UI for the secondary display by calling setContentView(). As an extension of the Dialog class, the Presentation class provides the region in which your app can display a unique UI on the secondary display.

Lockscreen Widgets

4.2 Jelly Bean brings widgets to the lockscreen. Android phone makers like Samsung and HTC have long been trying to fix the static lock screen in stock Android, adding some shortcuts to it, but now Google finally solves this problem. You can now sidescroll right to go into the camera and left to look at widgets. Out of the box there are only four widgets that you can add to the lockscreen, but third-party apps have already started offering lockscreen widgets, so in addition to the stock Gmail for example, you can have say a Twitter widget (via Plume for instance). Good news is that all of those lockscreen widgets are dynamically updated in the background. Whenever you receive a new email you can check it out straight from the lockscreen widget and without going into the mail app.

One word of caution though. Lockscreen widgets do not require a password. Even if you have your device password-protected, anyone can see the widgets without being asked for a password. That means that if you have a Gmail lockscreen widget, anyone who picks up your phone can read your emails on the widget (not in the app, though). This is not a bug, this is a feature. It is there for your convenience, so if you are concerned about the privacy of your email the solution is simple - don’t use those lockscreen widgets that reveal your information.

Multiple Users

Android now allows multiple user spaces on shareable devices such as tablets. Each user on a device has his or her own set of accounts, apps, system settings, files, and any other user-associated data.
As an app developer, there’s nothing different you need to do in order for your app to work properly with multiple users on a single device. Regardless of how many users may exist on a device, the data your app saves for a given user is kept separate from the data your app saves for other users. The system keeps track of which user data belongs to the user process in which your app is running and provides your app access to only that user’s data and does not allow access to other users’ data.

Saving data in a multi-user environment

Whenever your app saves user preferences, creates a database, or writes a file to the user’s internal or external storage space, that data is accessible only while running as that user.



Identifying users in a multi-user environment

If your app wants to identify unique users such as to gather analytics or create other account associations, you should follow the recommended practices for identifying unique installations. By creating a new UUID when your app starts for the first time, you’re certain to obtain a unique ID for tracking each user, regardless of how many users install your app on a single device. Alternatively, you can save a local token fetched from your server or use the registrations ID provided by Google Cloud Messaging.
Beware that if your app requests one of the hardware device identifiers (such as the WiFi MAC address, the SERIAL number, or the ANDROID_ID number), they will provide the same value for each user because these identifiers are tied to the hardware and not the user. Not to mention the other problems these identifiers introduce as discussed in the Identifying App Installations blog post.

New Global Settings

Next on the list of updates is Quick Setting, a menu of the most oft used toggles and shortcuts, designed to save the average user a trip to Settings. You bring this by either scrolling down from the top to bottom with two fingers, or bringing the notification shade and pressing the Quick Button icon in the top right corner.

Those are welcome additions - displaying things like the battery percentage, and allowing to set the screen brightness, but we do feel that Google could have easily gone with direct toggles for some of the things. Instead we get shortcuts. One glaring example is brightness. Instead of a brightness slider right into the menu, you have to first tap on a shortcut, and only then you get to adjust the screen brightness. That might be picking the nits, but we had to get it off our chests.


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