Binding asynchronously loaded images from a view-model about reactiveviewmodel HOT 3 CLOSED

The solution to the problem of the avatar download being kicked off as soon as the view model is initialized is solved by using the view model's active property and setting it to YES when the table view is about to display that cell (there's a UITableViewDelegate method for that). You can then set it to NO when the cell disappears, which could cancel the request. However, you'll be unable to use the rac_sendAsynchronousRequest: method because it's not cancellable; abstract out the network logic into its own class using the NSURLConnectionDelegate protocol. There are a few other opportunities to make your approach a little better, though.

You're not storing the image data anywhere, so it'll have to be re-downloaded every time a cell is displayed, which can get costly for the user's data plan. You should at least be caching them by url in a static NSCache instance, but more ideally storing them in the Person model. Second, UIImage's initWithData: method is expensive. I'd recommend this approach for decompressing on a background thread (note: simply using initWithData: on a background thread will not actually decompress the JPEG). As it is now, you'll likely see dropped frames while scrolling the table view.

Best of luck, and let us know how it goes!

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All good feedback, @ashfurrow – thanks! Using the active property makes sense. I'll take a look at that and return if I have any other questions.

Thanks again!

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FYI the same upgrade has beend done on FRP repo as I noticed the performance hit too (ashfurrow/FunctionalReactivePixels#27 & ashfurrow/FunctionalReactivePixels#30) Note that the performance hit may still be present as long as the code is compiled in debug mode.

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