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Loading with Loaders

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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!

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    [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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