Mark, Thanks for the reply!
> -- If you scroll enough before the image is done loading, and the row is > recycled first, you'll get weird results (image will keep flipping to > different pictures as its various tasks complete) Even if I never scroll, the results are still jumbled and/or duplicated. > 1. Rather than tie the AsyncTask to a specific ImageView, I have the > AsyncTask notify the ListView when an image load is complete, providing > it the URL of the loaded image. The ListView, when it inflates/recycles > rows, attaches the URL of the image that is supposed to be shown to each > ImageView via the setTag() method. Then, when the AsyncTask says > such-and-so URL is ready, the ListView walks the ImageViews and sees if > any are showing that image, by comparing the passed-in URL to each > ImageView's getTag(). If there's a match, ListView then loads the image > out of the AsyncTask-managed cache into the ImageView. This way, I don't > keep a strict tie between the AsyncTasks and the ImageViews. I suspect > there's a better-performing solution than my current implementation, but > it's at least tolerable for the moment. I'll code this up later and see if I have any problems. > 2. Rather than try to hack around the existing AsyncTask's limitations, > I copied its source code (thank you, Android and Apache 2!) and made it > use an unbounded LinkedBlockingQueue and use more than one thread to > process it. That beats the heck out of trying to keep your own queue to > feed into the AsyncTask class's static queue. Haha, yeah, that code could be cleaner, but it works pretty reliably, so I'm going to avoid replacing it until it becomes the problem. Evan Charlton On Sun, Jul 12, 2009 at 6:29 AM, Mark Murphy<mmur...@commonsware.com> wrote: > > Evan Charlton wrote: >> I will be surprised if this hasn't been asked before, but I've been >> Googling for days now and haven't found anything very helpful. My >> problem is this: >> >> I'm trying to lazy-load images into a ListView--almost exactly how >> Market does it, if you're familiar with that. It's not exactly like >> Market because the images there comes in batches whereas mine are one >> at a time, but I digress... >> >> I have the following adapter: http://paste2.org/p/318634 >> This adapter lazy-loads pages and each row's corresponding image (if >> applicable) and caches it to disk for faster loading next time. This >> all works perfectly *except* when loading images over the network, >> they come in on the wrong rows and are sometimes duplicated. I assume >> that this has to do with the adapter reusing views, but I haven't been >> able to stamp it out. > > I suspect you are on the money with your assessment of the problem. > > You pass in an ImageView to the AsyncTask and tell the task to replace > the image in that ImageView. However: > > -- Since it is asynchronous, for a bit, the ImageView will remain > unchanged, which in the case of a recycled row will be whatever it was > before > > -- If you scroll enough before the image is done loading, and the row is > recycled first, you'll get weird results (image will keep flipping to > different pictures as its various tasks complete) > > I just went through implementing something very similar. I'll eventually > tease it out into something reusable and open source. Compared to the > snippet of your implementation, here are two things I did differently: > > 1. Rather than tie the AsyncTask to a specific ImageView, I have the > AsyncTask notify the ListView when an image load is complete, providing > it the URL of the loaded image. The ListView, when it inflates/recycles > rows, attaches the URL of the image that is supposed to be shown to each > ImageView via the setTag() method. Then, when the AsyncTask says > such-and-so URL is ready, the ListView walks the ImageViews and sees if > any are showing that image, by comparing the passed-in URL to each > ImageView's getTag(). If there's a match, ListView then loads the image > out of the AsyncTask-managed cache into the ImageView. This way, I don't > keep a strict tie between the AsyncTasks and the ImageViews. I suspect > there's a better-performing solution than my current implementation, but > it's at least tolerable for the moment. > > 2. Rather than try to hack around the existing AsyncTask's limitations, > I copied its source code (thank you, Android and Apache 2!) and made it > use an unbounded LinkedBlockingQueue and use more than one thread to > process it. That beats the heck out of trying to keep your own queue to > feed into the AsyncTask class's static queue. > > -- > Mark Murphy (a Commons Guy) > http://commonsware.com | http://twitter.com/commonsguy > > Android 1.5 Programming Books: http://commonsware.com/books.html > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -~----------~----~----~----~------~----~------~--~---
