WebImage is an Android library which asynchronously downloads images from the internet and caches them for quick access. It has the following features:
- Images are downloaded in a background thread pool, keeping the GUI thread responsive.
- Images are cached to SD card, and if desired, also in a fast-access in-memory cache.
- If the user removes the SD card, the library will still work (albeit, without being able to save images to the file cache).
- Image cache removes old images, and can fetch HTTP headers to check if an image is expired and needs to be re-downloaded.
- Good performance, even on older Android 2.1 devices.
- Compatible with API level 7 and up.
- No additional library or framework dependencies!
- Builds quickly and easily with ant, or simply drop the tiny jarfile to your project's libs directory.
WebImage was written for Wrapp for use in our Android client in the summer of 2011 by Nik Reiman. We needed a library capable of handling a large number of asynchronous image downloads from the web without effecting the GUI, and with the exception of droid-fu the only code to do this exists in the form of StackOverflow answers.
This seemed to be a common wheel which many Android developers continue to re-invent, so we broke off some of our image handling code into a separate, modular library. Hopefully other developers will find it useful in their projects.
To use WebImage in your Android application, simply download the latest WebImage.jar file and copy it to your project's "libs" directory. You may need to configure your IDE to include jarfiles from this directory if you have not already done so.
Your project will need to declare the following permissions in the AndroidManifest file:
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
To actually download images, use the included WebImageView class, which is a
subclass of ImageView and has a method named setImageUrl(). This class can
be used either from XML layout files or in your classes.
Although you can override this class to provide post-processing on the
drawable (from outside of the GUI thread, even), you can also fetch raw
drawables asynchronously via WebImage.load().
During your application's initialization, you can configure WebImage's caching and logging behavior. Your individual activities can also tell the library to free memory, cancel pending requests, and so on. All of these tasks are detailed in the top-level WebImage class.
For more details, check out the source code, which is also bundled in the distribution jarfile. WebImage also has includes a some example projects which show how the library is most effectively used.
WebImage is licensed under the MIT license. See the file LICENSE.txt for more details.