The Problem with Activities

[MUSIC] 0:00 Hi, I'm Ben. 0:04 In this course, we're going to learn about the Activity Lifecycle. 0:06 In the Android operating system, almost all apps start and end with an activity. 0:11 Activities get created, paused, stopped and eventually, 0:17 destroyed and it's our responsibility as developers 0:21 to make sure that we handle each of these lifecycle changes gracefully. 0:25 There's a bunch of different lifecycle methods but before we get into that, 0:30 let's see why it's so important that we manage the activity lifecycle. 0:34 Here's the fun facts project from the very first course. 0:39 Let's see what happens when we get a new fun fact and then rotate the app. 0:43 Instead of showing the new fact, it's showing the first fact. 0:48 It turns out, activities are entirely recreated when the orientation changes. 0:52 At first glance, this probably seems a little weird but since different 0:58 orientations require different layouts, and those layouts require 1:02 different resources, activities are always recreated on an orientation change. 1:07 Since Android handles recreating the activity, 1:13 all we have to handle is saving and restoring our activity state. 1:16 For example, if a user is halfway down a giant list and 1:21 they rotate the app, normally, the activity will be restarted, and 1:25 they'll be looking at the top of the list. 1:30 But if we hook into the right lifecycle events, 1:33 we can save off their position in the list when the activity stops and 1:35 restore that position when it gets recreated. 1:39 That way, the user will be totally unaware of what just happened behind the scenes. 1:42 In the rest of this course, we'll see how we can use a bundle to 1:48 handle these kinds of changes, how we can save data using shared preferences and 1:51 we'll finish with a project that will you a chance to show off what you've learned. 1:56 It's a lot to cover. 2:00 Let's get started. 2:02