Android: Running a method in a separate thread asynchronously

Question

I have a method which refreshes a list view by re-setting the adapter of the list view. The adapter downloads a thumbnail image for each list item when it is set.

I want to run this method called refreshListView() on a new thread so that the images get downloaded asynchronously but i'm aware that i can't update the UI on a separate thread.

What are the alternative ways to do this?

Thanks in advance.

Kurtis Nusbaum · Accepted Answer · 2011-10-13T01:04:36.230

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You could use an AsyncTask ( http://developer.android.com/reference/android/os/AsyncTask.html) or a Loader ( http://developer.android.com/guide/topics/fundamentals/loaders.html). I recommend using a loader as it seems to be always easier. Both were (among other things) designed for exactly this type of problem.

In order to use the Loader on any target platform less than 3.0, please refer to http://developer.android.com/sdk/compatibility-library.html.

edited Oct 13 '11 at 01:04

answered Oct 11 '11 at 22:10

Kurtis Nusbaum

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Loaders are 3.0+ only, so they are not available on currently available phones. – Peter Knego Oct 11 '11 at 22:43
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@PeterKnego Not true. The android compatibility package give everyone access to loaders in a really easy way: http://developer.android.com/sdk/compatibility-library.html – Kurtis Nusbaum Oct 11 '11 at 22:45
Ahh, nice. Thanks for the info. +1 for answering first. – Peter Knego Oct 12 '11 at 06:05
@PeterKnego I added a little blurb to make that more clear in my answer. – Kurtis Nusbaum Oct 13 '11 at 01:05

score 2 · Answer 2 · answered Oct 11 '11 at 22:42

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Here is the entire code.

http://stackoverflow.com/questions/541966/android-how-do-i-do-a-lazy-load-of-images-in-listview/559781#559781

answered Oct 11 '11 at 22:42

dcanh121

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i got it working by setting the targetSDKVersion in the manifest to "2", the above code seems to load the images in a que. Is this the best way to load the images? Without setting the targetSDKversion to 2, only the placeholder image is displayed, the images don't seem to be downloaded – EI756 Oct 12 '11 at 08:17

score 1 · Answer 3 · answered Oct 11 '11 at 22:13

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AsyncTask also works for coordinating background jobs with UI element updates:

http://developer.android.com/reference/android/os/AsyncTask.html

answered Oct 11 '11 at 22:13

kramimus

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score 0 · Answer 4 · answered Oct 11 '11 at 22:18

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Hmm. If I understand right, you don't want to use the new adapter before the images have finished downloading? Where in the adapter is your image download code. Depending on that, you might only get to the download code once the adapter's views are being loaded/showed.

I usually download images first, in a background thread, and buffer them in a collection (of SoftReferences). Then, I have the adapter read from that collection when it loads.

answered Oct 11 '11 at 22:18

pumuckl

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Basically, the adapter is called like : "LazyAdapter lazyAdapter = new LazyAdapter(this, imagesListStringArray, listText1, listText2);" So the images are feeded through to the adapter with a string array which was populated before creating and setting this adapter – EI756 Oct 11 '11 at 22:23
In your above LazyAdapter constructor, is imagesListStringArray an array of Strings? Is each String an url to an image that you want to download? – pumuckl Oct 11 '11 at 23:53

score 0 · Answer 5 · answered Oct 11 '11 at 22:29

As previously mentioned, you can use AsyncTask which runs in another thread and can update the UI once the seperate thread has downloaded the thumbnails. Depending on how you want to implement it, you could also have the thumbnails update as they are downloaded by using the onProgressUpdate() method in AsyncTask. Otherwise use onPostExecute to reset the list adapter.

Android: Running a method in a separate thread asynchronously

5 Answers5