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Created attachment 25754 [details]
uwp listview problem demo
When u have a ListView that is a child inside a StackLayout then the rendering is extremely slow in UWP, even on a high end PC. You can actually see each row being added/rendered.
Same goes when the contents are scrolled.
But when not inside a StackLayout, the performance is OK.
Example attached. Check DemoPage.cs in the shared project.
Please test against the latest 2.5 stable and report back on whether it makes any difference. I do not experience the issue when running the provided reproduction against that version.
Tested it against the latest 220.127.116.11635. The problem still exists.
Running the project again to verify the original findings, there is minimal to no rendering of the list when the application loads, and none when scrolling. Ultimately, performance is dependent upon the device or computer's specs much like any other application. Visual rendering of items is not something that is Forms specific and can occur on regular UWP apps as the items are realized. In this case, this appears to simply be rendering working as expected.
The difference in performance when the ListView is inside a StackLayout vs when its not, is not XForms specific? Then why in Xamarin.UWP the UI native controls (Windows.UI.Xaml.Controls.ListView, stackpanel etc) perform entirely differently (a LOT better) vs Xamarin.Forms in the exact same hardware ?
Yes, hardware does make a difference, but how is it possible that plain Xamarin.Forms.ListView works great even in a slow tablet, while if using it inside a Xamarin.Forms.StackLayout in the exact same tablet everything get frustratingly slow ? Shouldn't Xamarin.UWP perform just as bad, in the exact same hardware instead of working great ?
A stated, no severe drop in performance was noted in this scenario using the reproduction. Without more information about specific hardware or a reproduction which guarantees that the behavior will be exhibited, we cannot move forward with this. Please refile an issue on GitHub with a more clearly defined scenario in terms of hardware setup where this issue may apparently be occurring, but for the time being this will be closed as no further reports of this kind have been made from other users regarding this issue.