[Image Loading] Display something better when in Preview

[chrisbanes]

Currently CoilImage, PicassoImage, and GlideImage all have different issues when used in @Preview. We should do something better.

• Make sure that using each of these functions does not crash the preview
• Think about adding a placeholder parameter to be displayed when in preview.

[Bradleycorn]

This may be a terrible/impossible idea (I'm still very new to Compose and in way over my head here), but ...

Is there some way that you can "detect" that the composable is being rendered as a preview?

If so, maybe when the *Image() composable detects that it's in preview mode, it attempts to use a (developer defined) PreviewImageLoader if it exists instead of its normal ImageLoader. Defining a PreviewImageLoader could be as simple as defining a map of the url's that are used in previews to local resources to load when one of the url's is found?

Or maybe you don't need the detection and PreviewImageLoader at all ... Maybe the developer could supply the standard ImageLoader with a map of url->drawable, and anytime the loader is asked to load one of those urls, it will use the drawable instead of trying to fetch the url.

Another (probably really bad) idea ... when the data parameter is parsed and is a string, check to see if it's a URL or if its specifies drawable (like "R.drawable.my_preview_image"). If it's determined to be a drawable, the actual resource could be parsed out, and the drawable loaded and returned. Something like this extension method on R.drawable could be used to parse the drawable string into an actual drawable int:

fun R.drawable.fromString(drawable: String): Int {
    try {
        val field = javaClass.getField(drawable.replace("R.drawable.", ""))
        return field.getInt(field)
    } catch (ex: Exception) {
        TODO("Uh oh!")
    }
}

[chrisbanes]

I like the idea of a PreviewImageLoader but ImageLoader isn't a class we own. Same for the equivalent classes for GlideImage and PicassoImage.

We could abstract these away behind a ImageLoadEngine class and do something similar though.

[github-actions]

This issue is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[chrisbanes]

Closing this, as previewPlaceholder was added a few releases ago.