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Threads and Runnables4:54 with Ben Deitch
In this video we talk about blocking the main Thread, and we see how to use a Runnable with a new Thread!
All right, let's run the app and see what happens. 0:00 If we click the Download button and 0:07 then wait ten seconds, one, two, three, 0:11 four, five, six, seven, eight, nine, 0:16 ten, we get a log message But 0:21 we didn't see our toast and if we click the Download button a bunch. 0:26 It looks like it stops responding. 0:33 And to top it all off, 0:38 we get the dreaded application not responding dialogue, or A and R.. 0:39 That's not good. 0:45 But why is this happening? 0:47 Remember that each Android app has its own main thread. 0:49 Sometimes called the UI thread. 0:54 And if we do too much work on the main thread, 0:56 then our UI can become unresponsive. 0:58 And we might see the application not responding dialogue. 1:02 We can fix this by putting the burden of our download 1:06 onto a different thread than the main thread. 1:09 We've seen this before when we built our weather app, Stormy. 1:13 We saw a highway where each lane was a different thread. 1:17 And we needed to be careful not to block the main lane with our downloading code. 1:21 In Stormy, we solved this by using a method from the OkHttp library that 1:26 handled all of this for us. 1:31 But this time we're going to create and user own threads. 1:34 Let's start by adding another lane to our highway by creating a new thread 1:39 object at the bottom of our OnClick method. 1:43 Let's type Thread thread = newThread and 1:50 notice that there are several constructors 1:55 we can use when creating a thread. 2:00 We'll be using the second one which takes a runnable. 2:05 A runnable represents a block of code that can be executed. 2:09 In our highway example, we can think of the thread as the lane and 2:14 the runnable as the traffic that flows on that lane. 2:18 Let's add our semi-colon. 2:22 And then add a couple of lines above. 2:25 And create a new runnable object. 2:31 Runnable runnable = new Runnable and 2:34 add a semi-colon. 2:40 Right now our runnable isn't running anything. 2:46 Let's cut out our download song method from above. 2:49 And paste it into the run method of our runnable. 2:54 And now that our runnable represents a bit more traffic on our highway. 3:01 Let's pass it into our thread's constructor. 3:05 Awesome, we've put the code that used to block our UI and a runnable and 3:12 that runnable is also add up to run on a new thread. 3:17 Now let's give our thread a name by calling Thread.setname and 3:21 let's name it DownloadThread. 3:29 The last thing we need to do is call thread.start to start our thread. 3:38 Great, now let's test the app. 3:47 Let's click the Download button. 3:56 And right off the bat, there's our toast. 4:00 And if we click it a bunch more, no problem. 4:03 Our button stays totally responsive and 4:09 we'll see a log message for each time it was clicked. 4:12 Great work! 4:18 But before we move on, let's take a minute to talk about what we learned here. 4:19 We can think of our app as one big runnable that runs on the main thread. 4:24 If we do a lot of work on this thread, like a download, 4:29 it can start to slow things down and the application might become unresponsive. 4:33 To solve this, we create a new runnable which contains our download code and 4:39 we run it on a new thread. 4:44 This way we can keep our download from blocking the main thread. 4:46 And more importantly, we can keep our users happy. 4:51
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