Why do the weather samples in FetchData seem to get cached for the sample Blazor app?

Question

The Blazor app in Visual Studio uses a Http.GetFromJsonAsync call to get the data for Weather Forecasts from a json file in wwwroot.

When I change the data in the file, I still see the same data in the table?

When I copy the file, and change the code to use the new filename, I get the changed results.

Is there some caching happening with wwwroot files? I've tried hard refresh, that doesn't make a difference, but changing browser does. I know that Blazor caches the framework files...but is this happening to all wwwroot, how do I change this behaviour?

Thanks in advance.

Answer 1

The fetchdata sample page (from new blazorwasm) retrieves data on initialize component:

protected override async Task OnInitializedAsync()
{
    forecasts = await Http.GetFromJsonAsync<WeatherForecast[]>("sample-data/weather.json");
}

When you go out of this page and come back, initialize is running again and a request is done.

But, because this is a GET request, the browser can deliver answer from cache:

They are some ways to avoid cache on Blazor GET requests, learn about it here: Bypass HTTP browser cache when using HttpClient in Blazor WebAssembly

Also, you can use the simple trick to add a random string to query string:

protected override async Task OnInitializedAsync()
{
    var randomid = Guid.NewGuid().ToString();
    var url_get = $"sample-data/weather.json?{randomid}";
    forecasts = await Http.GetFromJsonAsync<WeatherForecast[]>(url_get);
}

In short, it seems to get cached because a get request can be cached by browser and is the browser who retrieve the data.