Update the weather page in the Blazor Web App template to persist prerendered state

[Copilot]

Update the weather page in the Blazor Web App template to persist prerendered state

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Use [PersistentState] attribute in Weather.razor to avoid "Loading..." flash on direct navigation

Description

When navigating directly to the weather page in an interactive Blazor Web App, users see the prerendered content, then a flash of "Loading...", then the data again. This is particularly noticeable due to the 500ms simulated delay.

The fix uses [PersistentState] to persist the prerendered forecasts and restore them when interactive mode starts:

• Add [PersistentState] attribute to Forecasts property
• Change from private field to public property (required for attribute)
• Make WeatherForecast class public (required for JSON serialization)
• Skip data loading in OnInitializedAsync when state is already restored

@code {
    [PersistentState]
    public WeatherForecast[]? Forecasts { get; set; }

    protected override async Task OnInitializedAsync()
    {
        if (Forecasts is null)
        {
            await Task.Delay(500);
            // ... load forecasts
        }
    }

    public class WeatherForecast { ... }
}

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update the weather page in the Blazor Web App template to persist prerendered state</issue_title>
<issue_description>The weather page in the Blazor Web App template doesn't currently persist its prerendered state. This means that if the weather page is rendered interactively and you browse directly to the weather page, you'll see the weather prerendered, then replaced with Loading..., and then rendered again. The flash is particularly visible because we include the Task.Delay(500) to simulate loading the weather data.

</issue_description>

Comments on the Issue (you are @copilot in this section)

@ Thanks for contacting us.

We're moving this issue to the .NET 9 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.</comment_new>
<comment_new>@
Thanks for contacting us.

We're moving this issue to the .NET 9 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.</comment_new>

• Fixes Update the weather page in the Blazor Web App template to persist prerendered state #51205

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[Copilot]

Pull request overview

This PR updates the Weather page in the Blazor Web App template to use the [PersistentState] attribute, which eliminates the "Loading..." flash that occurs when directly navigating to the weather page. The feature works by persisting the prerendered weather forecast data and restoring it when the component becomes interactive, avoiding the need to reload the data and display the loading indicator.

Key Changes:

• Applied [PersistentState] attribute to persist weather forecast data across prerendering
• Converted private field to public property (required for state persistence)
• Made WeatherForecast class public (required for JSON serialization)