Hi Alex:
The icons and logos are loaded from a server on startup, and then kept up to
date via a 20 second polling pattern where the app checks if anything has
changed on the server. We timestamp all images and when one does change we get
latest and update the image in the app.
The way a ContentCache is used for BitmapImage and Image is to set the loader
like this:
public static var imageCache:ImageCache = new ImageCache(); // subclass of
ContentCache
_image.contentLoader = Model.imageCache;
_image.source = "https/someImageUrl"
When the image is first retrieved from the URL, the ContentCache loader will
save the image into a Dictionary (key/value pairs) where the key is the URL and
the value is the bitmapData of the image.
Then when using ItemRenderers, and they get recycled, the when the image URL
changes, ContentCache will look up the URL in it's Dictionary and if it's
already been downloaded it will simply display it without having to make an
HTTP request.
ContentCache is a very cool thing the Adobe engineers designed into Flex/Flash
and it makes lists with icons and pictures far more responsive.
What I want to do is persist the cache to disk and load it when the user logs
in again. If any image have changed since the last time they launched the app,
the first 20 second poll will indicate a timestamp has changed and the app will
retrieve images with a timestamp after the one returned when polling. So they
will always be up to date.
I said the images don't change but that's not actually true, they just don't
change often, maybe once a week we'll onboard new organizations and events with
images.
Embedding images is not an option because every new onboarded entity will
require a new app build, full regression testing, submission to Apple for
review and the entire release process. That's a bad business model.
Anyway, there must be a way in FileStream to save a Dictionary with key as
String and value as ByteArray, but I haven't figured it out yet. Was hoping
someone else knows how.
Thanks, Alex.
Erik
PS: I know how I can do this, but it's too much work the way I know how, I
would have to take each cached image, use pngencoder to encode the bitmapData
(ByteArray) to a PNG and save each image as a separate file. Last count our
image cache has about 1500 images so that means 1500 files, plus a hash file to
match the image URL to a generated filename for the image. Loading will then
require reversing the process. If you've used image encoders in Flash/AIR you
know they're pretty slow. If we don't gain any speed, it's not worth the
effort.
On Oct 26, 2018, at 3:44 PM, Alex Harui <aha...@adobe.com.INVALID> wrote:
Erik,
How do the icons and logos get into the cache in the first place? If they
don't change, is there any reason not to embed them in the application?
-Alex
On 10/26/18, 3:36 PM, "Erik J. Thomas" <e...@linqto.com> wrote:
Hey all:
Have any of you come across an example of persisting a ContentCache to disk
and reading it back on app launch? We have lots of icons and logos for hundreds
of companies and they don't change between sessions.
Like this (doesn't work though). ImageCache is a subclass of ContentCache to
get access to the protected cachedData:Dictionary which is key/value pairs,
with key as URL to image, and value is bitmapData.
public function saveImageCache(imageCache:ImageCache):void {
var cacheFile:File = File.applicationStorageDirectory;
cacheFile = cacheFile.resolvePath(IMAGE_CACHE_FILE_NAME);
if (cacheFile.exists) {
cacheFile.deleteFile();
}
var fileStream:FileStream = new FileStream();
fileStream.open(cacheFile, FileMode.WRITE);
fileStream.writeObject(imageCache.getEntries()); // this is a Dictionary
with byte array for image as value
fileStream.close();
}
The writeObject API of FileStream does not marshal the bitmapData to disk.
/**
* Loads a persisted image cache from disk.
*
* @return ContentCache
*/
public function loadImageCache():ImageCache {
var cacheFile:File = File.applicationStorageDirectory;
cacheFile = cacheFile.resolvePath(IMAGE_CACHE_FILE_NAME);
if (cacheFile.exists) {
var fileStream:FileStream = new FileStream();
fileStream.open(cacheFile, FileMode.READ);
var entries:Dictionary = fileStream.readObject() as Dictionary;
fileStream.close();
var imageCache:ImageCache = new ImageCache();
imageCache.loadEntries(entries);
return imageCache;
}
return null;
}
The entries variable does populate with all the keys as URLs, but the values
are null. FileStream won't read just raw binary data in this way.
I don't want to have to save every image using an encoder into separate
files and then load them all back if I can help it.
Just seems FileStream should be able to just write a blob of binary data to
disk and retrieve it "as-is" but it doesn't or I can't find the way.
Thanks for your suggestions.
Erik
