Batch CollectionChanged events

[symbiogenesis]

There are a bunch of places where there was some kind of bulk update on an ObservableCollection

By pulling in the ObservableRangeCollection from the XamarinCommunityToolkit and MvvmHelpers that is maintained by @jamesmontemagno we can see that there is some significant performance improvement to be had.

This could be done in many places across the codebase, in the future.

EDIT:

Just realized that there already was an ObservableList object that supports some range operations. It may be more suitable.

maui/src/Controls/src/Core/ObservableList.cs

Lines 10 to 14 in c02195d

	internal class ObservableList<T> : ObservableCollection<T>
	{
	// There's lots of special-casing optimizations that could be done here
	// but right now this is only being used for tests.

[ghost]

Hey there @symbiogenesis! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[symbiogenesis]

Updated this PR to add this optimization to another file.

I followed your advice, @jonathanpeppers, and did some profiling.

While running the sample app on Windows in this branch of my open source DataGrid, just scroll a lot. Or use the settings to try to toggle whether pagination is enabled, multiple times.

My speedscope results looked garbled and I couldn't get much knowledge out of PerfView except to see that there were tons and tons of threads. But Visual Studio memory profiling was intuitive. Still learning the tools.

That sample code is just using simple MAUI controls with nothing platform-specific, and shouldn't be super slow. The memory profiling showed tons of ItemTemplateContext objects and calls from ObservableItemTemplateCollection.

I already had this PR open to address this kind of issue involving ObservableCollections. So I knew that batching the CollectionChanged events was the right approach.

I could write another benchmark to try to prove that this is a better approach by orders of magnitude on large collections, but my latest update involving the ObservableItemTemplateCollection to this PR is Windows-specific and writing a Windows platform benchmark requires creating another project.

[AlleSchonWeg]

Hi @symbiogenesis
could you make the ObservableRangeCollection public? I missed this type of collection in MAUI. In XF we had such type in the xct.

[symbiogenesis]

Hi @symbiogenesis could you make the ObservableRangeCollection public? I missed this type of collection in MAUI. In XF we had such type in the xct.

That would be an API change that would need to be approved by the MAUI team. If they like this PR then the code will be there for them to expose as public whenever they like.

But I need to figure out why the tests are failing. So I will try to fix that now.

[symbiogenesis]

In reality, ObservableCollection itself should be updated to expose ranged operations, and this is one of the most-requested .NET features for years. A dev is claiming it is under consideration for .NET 9, but provided no promises.

dotnet/runtime#18087