Why does Sketch prototyping sometimes scroll, but other times scale my artboards?

Question

Still trying to wrap my head around Sketch and how it works. I have a bunch of PNG screenshots (iPhone 8 resolution so 750px wide, or 375@2x) and I want to build a quick click-through prototype in Sketch. Seems simple enough... create artboards for the pages, drag the images onto the artboards, then use the 'Fit' button to size the artboard to the content (which changes the height since the widths already match.)

The weird thing is when using the 'Preview' feature, some artboards show full-width and scroll (as I would expect), while other artboards show the entire artboard, scaled down to fit so it's tiny with huge black bars on the sides.

Checking the inspector on both the artboards as well as the images, I don't see any difference between those that scroll vs. those that don't.

Of note, some were created using the iPhone 8 template whereas others I tried using 'from selection' to save time. But still, I don't see any difference in the resulting artboard.

So what am I missing? How do I get my artboard to scroll, not scale?

Answer 1

Found it here...

TLDR: You need to explicitly choose a preset. Thought they were only used to create the artboards. Didn't realize they're actually a property of the artboard.

To fix, select your artboard that's acting up, then choose the preset you want to use for your viewport (choose a built-in size, or create your own.). Your artboard will remain the same size, but will now be associated with the iPhone's viewport.

Note: For this to work, you have to make sure your artboard's content has the correct width for the preset and that the height is at least as high as the preset, or else it will change to 'custom' and scrolling will break again.

HTH!

Answer 2

In my case I can't get it to scroll. I tried all the suggested workarounds I could possibly find (use preset art boards, resize them…), to no avail. It doesn't allow for scrolling or/and accurately resizing in Sketch Preview when looking at it on a desktop or laptop (only in Mirror on mobile it kinda works…). Plus, resizing the viewing/browser window (on desktop or laptop) shrinks or enlarges the page proportionally as a whole. That doesn't make any sense! 

What is this Preview supposed to be good for?! And without the ability to accurately preview and share the prototypes, prototyping itself becomes questionable.  How do you guys work around this? How do you Sketch users preview/share your prototypes (incl. resizing and scrolling)? Any tips are highly appreciated!