Image loading error reporting / handling

Lubomir Nerad lubomir.nerad at
Tue Jun 26 08:18:08 PDT 2012

Hi all,

I have two feature requests which ask for better error reporting / 
handling of image loading.

The issues are:

Make Image class support exceptions for both asynchronous and 
synchronous loading
Image/Media need consistent error reporting

Currently my idea of fixing them is through a new ImageLoader class.

This class will have two sets of instance methods for image loading:

Image load(...) - Used for foreground image loading. The difference 
between them and the Image constructors would be that by default (!) 
they will throw an exception if image loading fails [RT-17645] (instead 
of returning an Image with error set to true).

Image loadAsync(...) - Used for background image loading. Will throw 
only when input arguments are null or invalid.

Then there will be methods for registering image loading event handlers 
[RT-976]. I can think of the following basic set of events:

loading started (setOnLoadingStarted)
loading progress (setOnLoadingProgress)
loading finished
     loading succeeded (setOnLoadingSucceeded)
     loading failed (setOnLoadingFailed)

They will use a new ImageLoadingEvent and possibly 
ImageLoadingFailedEvent (with an added exception field). The 
ImageLoadingEvent will report the image for which the event has been 
generated (null for foreground images?).

Image loading errors will be reported as runtime (!) 

ImageLoader instances will be created through constructor(s) with 
possibility to pass some configuration parameters (for example the 
maximum number of images being loaded at the same time).

For "logging only" image loaders we might want to allow to configure 
(constructor parameter? loadingFailedEvent.consume()?) whether the load 
methods will throw ImageLoadingException or merely create Images with 
error flags set (as is the case of Image constructors).

This is just a basic outline of my proposal. We can focus on details 
when/if this approach is accepted. Alternatively the issues could be 
fixed by additional properties / methods on Image class. I didn't like 
it, because the added properties would be useful only during short 
period of the whole image lifetime and absolutely unusable for some 
images (images created from scratch). I also think that the ImageLoader 
approach makes uniform error handling of image loading easier (one 
handler for several images instead of one handler per image).

What is your preference / opinion about this?


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