Dec 4 2014

Getting Started with Activity & Fragment Transitions (part 1)

Activity and Fragment transitions in Lollipop are built on top of a relatively new feature in Android called Transitions. Introduced in KitKat, the transition framework provides a convenient API for animating between different UI states in an application. The framework is built around two key concepts: scenes and transitions. A scene defines a given state of an application’s UI, whereas a transition defines the animated change between two scenes.

When a scene changes, a Transition has two main responsibilities:

  1. Capture the state of each view in both the start and end scenes, and
  2. Create an Animator based on the differences that will animate the views from one scene to the other.
Jan 13 2014

Thread Scheduling in Android

This post will give an overview of how thread scheduling works in Android, and will briefly demonstrate how to explicitly set thread priorities yourself to ensure that your application remains responsive even as multiple threads run in the background.

For those who are unfamiliar with the term, a thread scheduler is the part of the operating system in charge of deciding which threads in the system should run, when, and for how long. Android’s thread scheduler uses two main factors to determine how threads are scheduled across the entire system: nice values and cgroups.

Jan 8 2014

Redesigning Android Design Patterns

A couple weeks ago, I began the ambitious task of rewriting this blog from scratch. Today, I’m happy to introduce a brand new look: one that is cleaner, faster, and more responsive.

Several of the major changes are listed below. If this is your first time visiting this blog, you can find the old version of the site here to use as a reference.

Aug 20 2013

Fragment Transactions & Activity State Loss

The following stack trace and exception message has plagued StackOverflow ever since Honeycomb’s initial release:

java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState

This post will explain why and when this exception is thrown, and will conclude with several suggestions that will help ensure it never crashes your application again.

Aug 5 2013

Binders & Death Recipients

Note: before you begin, make sure you’ve read my previous post about Binder tokens!

Since the very beginning, Android’s central focus has been the ability to multitask. In order to achieve it, Android takes a unique approach by allowing multiple applications to run at the same time. Applications are never explicitly closed by the user, but are instead left running at a low priority to be killed by the system when memory is low. This ability to keep processes waiting in the background speeds up app-switching later down the line.

Developers learn early on that the key to how Android handles applications in this way is that processes aren’t shut down cleanly. Android doesn’t rely on applications being well-written and responsive to polite requests to exit. Rather, it brutally force-kills them without warning, allowing the kernel to immediately reclaim resources associated with the process. This helps prevent serious out of memory situations and gives Android total control over misbehaving apps that are negatively impacting the system. For this reason, there is no guarantee that any user-space code (such as an Activity’s onDestroy() method) will ever be executed when an application’s process goes away.

+1 this blog!

Android Design Patterns is a website for developers who wish to better understand the Android application framework. The tutorials here emphasize proper code design and project maintainability.

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