Changed css classes assignment in RenderPlaceholderRow

[dariatiurina]

Changed css classes assignment in RenderPlaceholderRow

Description

This pull request includes a change to the QuickGrid.razor. The update introduces logic to check for custom placeholder templates and adjusts the CSS class applied to the cell accordingly.

Changes:

• src/Components/QuickGrid/Microsoft.AspNetCore.Components.QuickGrid/src/QuickGrid.razor: Added a check for whether a column has a custom placeholder template (PlaceholderTemplate). If it does, a specific CSS class is applied; otherwise, a default "grid-cell-placeholder" class is included. This ensures better styling and flexibility for placeholder content.

Fixes #49440

[Copilot]

Pull Request Overview

This PR updates the placeholder rendering in QuickGrid.razor to apply a default CSS class only when no custom placeholder template is provided, and adds a new async virtualization QuickGrid scenario with corresponding E2E tests.

• In QuickGrid.razor, introduced logic to check for PlaceholderTemplate and conditionally include the "grid-cell-placeholder" class.
• Added a new VirtualizationQuickGrid.razor test component demonstrating async loading with custom and default placeholders.
• Updated Index.razor and VirtualizationTest.cs to wire up and verify the new QuickGrid virtualization scenario.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Components/QuickGrid/Microsoft.AspNetCore.Components.QuickGrid/src/QuickGrid.razor	Conditionally set placeholder CSS class based on presence of custom template
src/Components/test/testassets/BasicTestApp/VirtualizationQuickGrid.razor	New test component demonstrating async QuickGrid virtualization with placeholders
src/Components/test/testassets/BasicTestApp/Index.razor	Added menu option for VirtualizationQuickGrid in the sample app
src/Components/test/E2ETest/Tests/VirtualizationTest.cs	Added E2E test PlaceholdersHaveCorrectValue_Async to verify CSS classes and content
src/Components/test/testassets/Components.TestServer/RazorComponents/ComplexValidationComponent.razor	Minor change to <p id="is-interactive"> content

Comments suppressed due to low confidence (1)

src/Components/test/testassets/BasicTestApp/VirtualizationQuickGrid.razor:34

• The TaskCompletionSource is missing a generic type parameter, which will cause a compilation error. Specify a type argument (e.g., TaskCompletionSource<object?>) and update SetResult calls accordingly (e.g., SetResult(null)).

    TaskCompletionSource asyncTcs = new TaskCompletionSource();

[Copilot]

[nitpick] Consider trimming the combined class string to avoid leading whitespace when placeholderClass is empty, for example using class="@($"{placeholderClass} {ColumnClass(col)}".Trim())".

Suggested change

	<td class="@placeholderClass @ColumnClass(col)" @key="@col">@{ col.RenderPlaceholderContent(__builder, placeholderContext); }</td>
	<td class="@($"{placeholderClass} {ColumnClass(col)}".Trim())" @key="@col">@{ col.RenderPlaceholderContent(__builder, placeholderContext); }</td>

[javiercn]

This not only affects the ... but also the opacity. (See https://github.com/dotnet/aspnetcore/blob/main/src/Components/QuickGrid/Microsoft.AspNetCore.Components.QuickGrid/src/Themes/Default.css).

I think that rather than conditionally adding/removing the class (which will make things harder for us in the future), we should keep the class and add an extra class (let's say "default" for the discussion but find a better name).

Something like

.quickgrid[theme=default] > tbody > tr > td.grid-cell-placeholder.default:after {
    content: '\2026';
    opacity: 0.75;
}

This more closely follows "BEM" (Block-Element-Modifier) and essentially still allows people to target the placeholder indistinctively if they want to.