Blazor Virtualize: ItemsProvider called repeatedly after scrolling just far enough to load more items #28653
Description
Describe the bug
The initial render with ItemsProvider works well with an EF Core data source with around 3800 items. Scrolling just enough to cause the ItemsProvider to be called again results in it being called repeatedly. After many calls, the page becomes unresponsive. Here are a couple VS console log samples of what's happening. You can see there's a bit of a pattern between the 2 samples.
{ItemsProvider call count}: {ItemsProviderRequest.StartIndex} {ItemsProviderRequest.Count}
Sample 1
1: 54 15
2: 3 15
3: 6 15
4: 0 15
5: 1 26
6: 1216 20
7: 10 15
8: 23 15
9: 10 15
10: 23 15
11: 10 15
12: 23 15
13: 10 15
14: 23 15
15: 10 15
16: 23 15
17: 10 15
18: 23 15
19: 10 15
20: 23 15
21: 10 15
22: 23 15
23: 9 15
24: 0 15
25: 25 15
26: 9 15
27: 23 15
Sample 2
1: 54 15
2: 3 15
3: 7 15
4: 0 15
5: 1 37
6: 1791 23
7: 81 58
To Reproduce
Here is the code involved:
<Virtualize Context="item" ItemsProvider="LoadItems" ItemSize="100">
<ItemContent>
<CascadingValue Value="item">
<Item />
</CascadingValue>
</ItemContent>
<Placeholder>
<p>Loading</p>
</Placeholder>
</Virtualize>
@code {
[Parameter]
public IQueryable<Item> Items { get; set; }
[Parameter]
public int ItemsCount { get; set; }
private int _callCount = 0;
private async ValueTask<ItemsProviderResult<Item>> LoadItems(ItemsProviderRequest request)
{
var numItems = Math.Min(request.Count, ItemsCount - request.StartIndex);
var context = ItemsService.GetContext();
var items = await context.Items.Skip(request.StartIndex).Take(numItems).ToListAsync();
Console.WriteLine($"{_callCount}: {request.StartIndex} {request.Count}");
_callCount++;
return new ItemsProviderResult<Item>(items, ItemsCount);
}
}
Exceptions (if any)
There may or may not be some of these:
Exception thrown: 'System.Threading.Tasks.TaskCanceledException' in System.Private.CoreLib.dll
Further technical details
- ASP.NET Core version: 5.0.1
- The IDE (VS / VS Code/ VS4Mac) you're running on, and it's version: VS Mac