[MUSIC] 0:00 When we last saw stormy, it was just that pretty storming and 0:04 not working due to a network on main thread exceptionary. 0:08 As the name would indicate, we were getting the error because our 0:13 app was trying to get data while on the main thread. 0:16 So what exactly is a thread? 0:19 We're supposed to be doing entry development, not sewing. 0:22 Let's talk about this concept of threads, as it relates to apps and 0:25 computer programs in general. 0:29 We've all experienced this at some point with our phones and 0:31 it can cause lots of frustrations. 0:34 You do something in an app, and the app lags. 0:37 You tap somewhere else on the screen and nothing happens. 0:40 Tap, tap, tap and no response. 0:43 As good responsible developers, we want to make our users happy with our apps. 0:47 One way to accomplish this is to ensure responsiveness to input from the user. 0:52 We never want to leave it in a frozen state. 0:57 To accomplish this, we perform work on separate threads of execution in parallel. 1:00 Let us take a look at an example. 1:06 Let us think about a conversation we are having with a friend. 1:08 Generally, we want to be responsive to their input, right? 1:12 No one enjoys having a one way conversation. 1:15 If I'm talking to Ben I don't want to roughly leave the conversation to go get 1:18 water, that will leave him waiting and frustrated. 1:22 Typically, I'd wait to finish the conversation and 1:26 then get my work in water. 1:28 You know, do two things in order. 1:30 This is know as performing synchronous tasks. 1:32 What if I'm really thirsty though? 1:35 I could ask someone else to go get me some water while I'm talking with Ben. 1:38 That work, getting water, is done in parallel with my main work, 1:42 the conversation with Ben. 1:46 On an Android device, and most computers, 1:49 all the work is typically done on one main thread of execution. 1:52 My conversation with Ben is like work being done on the main thread. 1:57 We can perform additional work in the background like getting water 2:01 by executing it on a separate asynchronous thread of execution. 2:05 This background thread, Craig here in this example 2:10 can perform long running operations that would otherwise clog up the main thread. 2:14 What do I mean by a thread of execution? 2:19 In programming, we use the term thread to refer to a path of execution for code. 2:22 We can make our code perform multiple tasks at once, 2:28 just like the conversation and water example we just explored. 2:31 This is known as concurrency which means 2:35 having multiple things happen at the same time. 2:38 How does this relate to Android programing? 2:41 Android has many ways to handle asynchronous processing. 2:44 Further, it's built right into okay HTTP. 2:48 We'll explore that more here shortly. 2:53 Why are we even talking about this, well, just like our conversation and water 2:55 example, we want our app to be completely attentive and responsive to our user. 3:00 You can think if the Android operating system as a highway with multiple lanes. 3:06 Each lane is a thread used for processing code. 3:11 On this highway, we have vehicles speeding along. 3:15 Think of these vehicles as code executing in different apps or 3:18 different parts of the system. 3:21 The code we just wrote is synchronous code. 3:23 This is like blocking the lane with a slow moving truck. 3:26 When we write asynchronous code, we move this truck to another lane, and 3:30 it keeps the traffic on the main lane flowing as normal. 3:34 Let's think about networking on this highway. 3:38 We all know that the network can be a little unreliable at times. 3:41 When we make a network call on our app what happens if we have issues and 3:46 our request takes a long time? 3:50 We're making that all on our main thread like we are in our code right now. 3:52 It can block the user interface. 3:56 None of the user interface code will get executed and 3:59 the user won't be able to do anything with the app. 4:01 They would think it is unresponsive or broken, leading to frustration and 4:05 then they might even, delete our app. 4:09 All of our networking code should be done in a background thread. 4:13 One of these side lanes. 4:16 This way, we won't block the UI from being responsive. 4:18 When this network request completes, we need to move back 4:22 from the background thread to the main thread to update our UI, 4:25 since all of UI updates are done on the main thread. 4:29 That's a lot to take in, I know, but concurrency can improve the responsiveness 4:33 of our code by ensuring that our main thread is free to respond to user events. 4:39 Our next step, then, is to change our code to be asynchronous. 4:44 Let's see how we can do that, next. 4:48