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Why Loaders?2:10 with Ben Deitch
In this video we'll learn what problems we can solve by using Loaders!
[MUSIC] 0:00 Hi, I'm Ben. 0:04 And in this workshop, we're going to learn about Loaders. 0:06 Loaders are one of the ways we can do work on a background thread. 0:08 But more importantly, Loaders are not attached to activities. 0:13 So if you spend a long time downloading something with a Loader, and 0:17 then rotate the device, even though the activity would have been killed, 0:20 the loader will be just fine and ready to give you your data. 0:24 To see why we need Loaders, let's take a look at some code that loads images into 0:29 a recylcerView using an AsyncTask. 0:34 You can find the code and 0:36 the blog post this code was taken from in the teacher's notes below. 0:37 So when this app is launched, we start by setting up a progressBar and 0:41 a recyclerView. 0:44 Then, we kickoff an AsyncTask to load ten images. 0:47 And while those images are loading, we're going to figure out how much progress 0:52 we've made, And update the progressBar after each one finishes. 0:56 Finally, when we're done loading the images, we hide our progressBar and 1:05 update the recyclerView. 1:10 So what's wrong with this code? 1:15 Let's run it and find out. 1:17 So far so good. 1:27 We saw the progressBar and we've got our images. 1:28 But if we rotate the app, 1:32 It starts loading a whole new set of images, not good. 1:35 This is where Loaders come in. 1:40 By using a Loader instead of an AsyncTask, 1:42 we can make sure that we only download something once. 1:44 The Loader can keep a cache of what we downloaded. 1:48 And if we try to download it again, instead of actually doing it again, 1:51 the Loader will just give us our cache data. 1:54 Even if we rotate the app in the middle of a download, with Loaders, 1:58 it'll just keep on doing it's thing in the background. 2:01 And once it's done, we'll get the update in our new activity and 2:04 everything will be just peachy. 2:08
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