Hi,
Don’t suppose anyone know a way to prevent the following?
When inserting an object in the scrollView during the scroll release slow down, scrolling halts.
I suspect this is because of the automatic recalulation of the scroll view height, but havent found a way to prevent or delay this.
The scenario is that I dont want scrolling to stop during progressive loading.
Anaqim
Make sure you have more objects in the scroll than it is tall.
Use placeholder fills (like a 16x16 transparent image) for off-screen objects.
Detect the drag portion of the interaction and detect whether more objects will be needed before the finger is released and momentum takes over. If so, add objects then.
Following these steps will ensure you don’t run out of elements to show, you don’t waste memory on fills for offscreen objects, and you don’t stop the momentum part of the scroll.
Also, don’t forget you can download and modify the widget library to suit your needs.
Hi roaminggamer,
I forgot to mention that what populates the list are images from the loadRemoteImage callback, in batches of 50 small images.
When they are created, I insert them into the list as they arrive.
Of course I can wait until all are downloaded and insert all in a loop but whichever way i do this, the resizing of the scrollView halts the slowdown momentum.
Point 1 is given but to my knowledge, I cant use a placeholder and then replace it with a different object since i’d have to insert the new one anway after destroying the old, and scrollView will always recalculate heigh (in my case) when an object is inserted. Or am i wrong?
Point 3 is gonna be hard as I do not know when the images will be finished loading.
What i’ve done as an alternative solution to keep scrolling smooth is that once the scroll reaches the end, it freezes, pops a loading tag, and once all is downloaded and checked, removes the tag and unlocks for forther scrolling.
It works quite well, albeit not exactly how I wanted in the first place.
You don’t need to wait till they are downloaded.
Put a placeholder rect or imageRect in the scroller of the correct dimensions.
Fill it with a blank texture or just use an empty rectangle.
Request the image and attach a listener to the rectangle.
When the request comes in, fill the rectangle with the texture.
Tip: This may be complicated a bit if you don’t know the size of the image till it arrives. If this is the case, either:
A. Use a rect in a container and scale the rect when its image comes in.
B. Mask the rect and do the same scaling.
Here are two basic examples of the temporary fill concept:
https://github.com/roaminggamer/RG_FreeStuff/raw/master/AskEd/2016/09/remoteFiles.zip
https://github.com/roaminggamer/RG_FreeStuff/raw/master/AskEd/2016/09/remoteFiles2.zip
These don’t include scrolling or culling off-screen objects, just placing a temporary rect, then filling with the downloaded image when it arrives.
https://www.youtube.com/watch?v=DBjfUR68hLQ
I have an offscreen culling example somewhere, but I can’t remember where it is right now.
If you want me to put together a working example for you we might be able to work something out.
Note: You seem to be unclear on one point.
I’m not saying replace the object. I’m saying to set the fill with the image when it is available.
You can change the fill of any rect or imageRect.
Thanks mate!
Need to study what you are saying here.
Only have 9 months of corona and lua under the belt and little programming experience before that.
Will let you know how it goes!
Note: If you want to till the scroller on the fly from remote images whose size you do not know and you also want those images to be shown full sized, then this will be a bit harder, but probably not impossible.
However, that sounds like bad design to me. I’d change the design so that all images must be displayed at a uniform size, even if that means you scale and or clip parts of the image when it arrives.
In this case, a little uniformity in the design rules will help a lot.
I’m about to take of, but last note.
I’ve made exactly the kind of scroller, filled with currently downloading images before as part of more than one app.
Assuming certain constraints, this is actually pretty straightforward.
The only tricky bits are:
Handling odd sized images of unknown dimensions.
Culling off-screen objects for efficiency. i.e. Re-fill offscreen images with the shared 16x16 texture. This keeps memory usage down a lot.
cut my code down to bare minimum to figure this out and found that the culprit to this hick-up is that i do my progressive preload check in the scrollView event which only fires when finger is on the board. The release slow down scrolling does not fire any events.
I’ll fix this with a enterFrame runtime check instead tomorrow. it should work.
thanks for the tip on how to use placeholders!
anaqim
@anaqim, scrolling stops because of 1 line of code in the scrollView and is easily fixed by downloading the widget library from github.
This thread explains the fix - https://forums.coronalabs.com/topic/68105-scrollview-speed-limit-and-scrolling-abruptly-stopping-when-adding-new-elements-within/?hl=%2Bscrollview+%2Bstops+%2Bscrolling
In my case the rect fill doesn’t work as I have lots of text objects and filters. Plus doing dynamic insert/remove saved over 70MB RAM so it was win/win.
Hi sphere,
Thanks! that sounds like something worth checking out first thing in the morning 
Hi again sphere,
Read the post you linked to and wonder if you’d mind sharing the improved dynamic load/unload version of this script that you fixed? It’s exactly what i’m looking for.
If not, thats fine too, just want to know before I “get to it”.
Cheers!
downloaded the script from github, removed the line in question, and tried to require it and use it, but it seems i’m too inexperienced to get it to work in my code.
all i need is to get rid of that pesky line that stops the scrolling.
any pointers is appreciated as to how i setup/use the modified script
got the dynamic loading/unloading of images working in the scroll so now all I am missing is to get that scroll stopper fixed.
if anyone has the knowledge and the time?
There are some internal referencing issues that need addressing if I remember correctly - check all the requires have valid paths. This will depend on how you have the project physically laid out.
thanks for the hints but its beyond my capabilities i’m afraid.
i have to try and find another way to do this then.
It seems I have not choice but to try and solve this somehow.
This link describes the problem and the fix, but I need someone more skilled to either help me or guide me on how to do it, as my feeble attempts remain unsuccessful. I am able to edit the error but not to execute/use it.
I would appreciate it a lot.
Anaqim
I finally found a working solution.
To help anyone else experiencing the same sudden scroll release stop when adding content to the view, here is how i did it.
Go to https://github.com/coronalabs/framework-widget and download the widget_scrollview.lua file from within the widgetLibrary folder.
Comment out or remove line 438, which looks like this: “self:scrollToPosition( { x = origX, y = origY, time = 0 } )”
Save the lua file and copy it to the root of your project.
Scrolling should now work perfectly without changing anything in your own lua code.
I am not entirely sure why this works, but I am guessing that when the widget code looks foor lua files, it defaults to the root directory, and as such overrides the old file with the new edited one.
This problem/bug needs to be fixed by Corona with a simple deactivate option to accommodate all users and uses.
I’ve spent almost a week in frustration trying to work around and/or fix this, and frankly, official support could have been better.
Anaqim
UPDATE!!!
It seems this is not fixed after all and I am at loss what to do.
The above solution works with a win32 build but not in the simulator, nor on android.
Ideas?
I’m pretty sure the local copy of the lib is NOT getting used.
Simply dropping it in the root folder isn’t enough. The widget library preloads the first time it is required, and you have to do some specific things to get your local changes to be used.
I have outlined this before in another thread:
https://forums.coronalabs.com/topic/68339-categories-rows-on-tableview-doesnt-display-the-right-one/
PS - Please don’t vent on the staff. I realize you may be frustrated, but lets be clear. Their time is worth gold. While your week spent has probably been educational. Additionally, this feature may not be so universally useful to warrant adding it to the standard builds.
Finally, features are not changed based on posts in the forums except on rare occasions. There are two ways to get changes into Corona:
File a bug using the bug link.
File a feature request.
PPS - Don’t forget. Time is money for us all. I and others try to help a little for free, but this goes against time we could spend making money. I personally offer a paid service for situations exactly like this, where more help is required than I can afford to give for free.
https://forums.coronalabs.com/topic/69420-hire-a-hitman-problem-solver-is-back/
This may seem simple “to fix” but we were going through it last night and there are lots of potential ramifications to removing that line. No-one likes “fixes” breaking their existing code.
You really are better of customising the widgets library to your implementation as this will certainly be quicker. I’d recommend you let Ed (aka roaminggamer) help you with this as unfortunately I am far too busy.
A horizontal tableView would be the answer and I am pushing for this, but again this is not going to be anytime soon.