What is default image preloading behavior? about react-native-image-gallery HOT 9 CLOSED

It is not well documented, yes. But it describes where you should fetch docs from. Since FlatList is actually a VirtualizedList: https://facebook.github.io/react-native/docs/virtualizedlist.html#windowsize

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Since v2.0.0, this module relies on FlatList. This is the only thing that will affect the rendering logic of each image.

For now, I left the optional optimizations of the component blank. I will keep an eye on the performance of galleries with a large number of items and/or big images and see if it's important to either provide these optional props for FlatList, or at least let the users provide their own if they need to tweak it.

So, to give you an answer, if FlatList is behaving how react-native describes it, it should render enough images to fill the whole list horizontally, so, only one.

Actually, I'm pretty sure it's not doing that behind the scenes. FlatList is far from being totally finished and is still riddled with bugs and regressions across versions.

I don't want to over-optimize things yet, but if the need arises we'll release a version that renders items in a more optimized way, especially on the first render.

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By default FlatList renders the currently viewed screen + 10 more in any direction. This means you ould normally end up with 21 rendered screens.

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@vbuch this is interesting, is this documented anywhere ? Or did you peak at the source code ? FlatList is still shady right now.

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So in the case of this image gallery setting windowSize={3} should be exactly what's needed.

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I didn't know about this prop, it might be good to allow users to pass props to FlatList directly then.

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Having it set to 3 by default is a good idea though. In most usecases of the gallery you would only need three. You cannot actually scroll past a couple of images, right?

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I agree with @vbuch, preloading 10 images at the startup is causing initial render of the application slower. This is the reason I rolled back to version 1.1.0 and wrote my own logic using Image.prefetch to preload 3 images.

Version 1.1.0 was not showing any default preloading behavior.

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@syedabdulbaqi you could give this pull request a try and confirm if @Exilz should review it.

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