How to Refresh a Blazor Main Razor Page from Child Components After an API Call?

Trigger/refresh the main .Razor page after the Blazor subcomponent API call is completed

In Blazor, we often encounter situations where we need to dynamically update the main page layout or refresh content based on events or actions triggered in nested child components (such as API call completion).

Actual case

Consider the following scenario:

• We have a main search page with multiple filter components (e.g. SearchResults.razor).
• When the user applies a filter, we call the API endpoint to get the modified data.
• We want to display the updated data and hide the loading spinner on the SearchResults.razor page after the API call completes.

Solution

To achieve the above solutions, we utilize the following technologies:

1. Implement stateful services

We use scoped services (such as AppState) to store and share the retrieved API data so that it can be accessed by both the root page and its subcomponents.

2. Create the "loading" component

We define a reusable Loading.razor component that displays the spinner when the page loads and content when the data is ready.

3. Use view service

We create a view service (e.g. WeatherForecastViewService) that manages the data and exposes a ListChanged event that is fired when the underlying data changes.

4. Bind the subcomponent to the view service

In the child component, we inject the view service and monitor its ListChanged event. After a change is detected, we use StateHasChanged to refresh the component and display the updated data.

5. Centrally manage status on the root page

In the main SearchResults.razor page we:

• Bind the Loading component to AppState to show or hide the spinner based on data availability.
• Inject the view service using dependency injection.
• Get data and update AppState asynchronously.
• Listen to the view service's ListChanged event and call StateHasChanged to trigger UI updates.

Code snippet (SearchResults.razor)

<code class="language-csharp">@code {
    [Inject] WeatherForecastViewService viewService { get; set; }

    // API 调用完成后赋值为 true
    public bool IsLoaded { get; set; }

    protected override async Task OnInitializedAsync()
    {
        await GetForecastsAsync();
        this.viewService.ListChanged += this.OnListChanged;
    }

    private async Task GetForecastsAsync()
    {
        // 代码省略，为简洁起见
    }

    private void OnListChanged(object sender, EventArgs e)
        => this.InvokeAsync(this.StateHasChanged);

    public void Dispose()
    {
        this.viewService.ListChanged -= this.OnListChanged;
    }
}</code>

Code snippet (Loading.razor)

<code class="language-csharp">@if (this.IsLoaded)
{
    @this.ChildContent
}
else
{
    // 显示加载微调器
}</code>

By implementing these techniques, we establish a communication channel between child components and the main page, allowing us to trigger UI updates and maintain consistent data state across parent-child relationships.

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