[Bug] Listview on wpf takes takes a lot to clear when changing itemsource

[observer1]

Description

Listview on WPF takes a lot to clear thounsands of items

Steps to Reproduce

1. Create a listview and fill with thousands of items
2. Change the itemsource to a list of the same type but empty
3. It will take a lot of time

Expected Behavior

The listview should clear instantly

Actual Behavior

The listview takes a lot of time to clear

Basic Information

• Version with issue: 4.4.0.1233-nightly
• Last known good version: none
• IDE: VS 2019
• Platform Target Frameworks: WPF
• Android Support Library Version:
• Nuget Packages: Xamarin.Forms Xamarin.Forms.Platform.WPF
• Affected Devices: Windows 10 pc

  Screenshots

Reproduction Link

Test - Copy.zip

[yurkinh]

I'm not sure that this is 100% correct solution but If in ListViewRender replace lines [286-290] foreach (var item in TemplatedItemsView.TemplatedItems) { items.Add(item); } _listview.ItemsSource = items; with line _listview.ItemsSource = TemplatedItemsView.TemplatedItems; it will start working blazingly fast. This is is only for ungrouped data. I have attached working solution with modified ListViewRendere TestList.zip

[yurkinh]

In original sample, the problem is with unhooking events (UnhookAndClear() method is called 20000 times for each of item). In UWP we don't have such issue : UnhookAndClear() method has not been called at all.

[jfversluis]

Taking into consideration the remaining lifetime of Xamarin.Forms, the platform this is about, the age of this issue and the traction this issue has seen I think it's unlikely that this will get fixed. If it is something that you still would like to have, please consider opening a PR. Thanks!