Blazor Wasm: Virtualize component making 3 initial calls to ItemsProvider instead of 1

[bancroftway]

When using Virtualize component with ItemsProvider, I have noticed that the ItemsProvider is always called 3 times on the first render. This may be slightly excessive if we are calling an api inside the ItemsProvider.

As an example, I have a collection of 15000 items. On first render, the Virtualize component made 3 calls into the ItemsProvider:

1. Request Count=20, Start Index=0
2. Request Count=21, Start Index=14979 (=15000 - 21)
3. Request Count=21, Start Index=0

I am guessing that the component is doing this for some initial setup calculations of the scroll bar etc...however, the question is whether these 3 calls can be obviated by a single initial call, or is there a way to specify any additional arguments to the component perform its setup without performing 3 calls into ItemsProvider.

Reproduction is here: https://github.com/bancroftway/blazorissuesrepro/tree/dotnet5vscoll

A small video demo is here: https://www.youtube.com/watch?v=5BnRgZTpO0M

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[mrlife]

I can confirm something similar is happening on Blazor Server. The ItemsProviderRequest content is unexpected.

For a collection of 107 items, it varies:

1. Request Count=11, Start Index=0
2. Request Count=80, Start Index=27
3. Request Count=116, Start Index=0

And

1. Request Count=11, Start Index=0
2. Request Count=54, Start Index=53
3. Request Count=115, Start Index=0

Since my Virtualize contains EF Core code in a descendant component, I get the "A second operation was started on this context before a previous operation completed" unless I save the return value of the first call and return it for calls 2 and 3.

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