How to Refresh a Main Razor Page from Sub-Components After an API Call in Blazor?

Refreshing a main Razor page from sub-components in Blazor after an API call requires a state management approach. Blazor's built-in change detection mechanism won't automatically update the parent component unless its data properties change. Here's how to implement a robust solution using a state/notification pattern:

To achieve this, we'll use a service to manage application state, injecting it into both the main page and its sub-components. The sub-components will trigger notifications in this service after API calls, prompting UI updates.

1. Create a State Management Service:

This service will hold the data and a mechanism to notify subscribers of changes. We'll use an EventCallback for this purpose.

using Microsoft.AspNetCore.Components;

public class StateService
{
    public event Action StateChanged;

    // Your application state data
    public string DataFromAPI { get; set; } = "";

    public void NotifyStateChanged()
    {
        StateChanged?.Invoke();
    }
}

2. Inject the Service into Components:

Inject the StateService into both your main Razor page and the sub-components that make API calls.

@inject StateService StateService // In both the main page and sub-components

3. API Call and State Update in Sub-Component:

In your sub-component, after a successful API call, update the StateService's data and notify of the change.

@code {
    protected override async Task OnInitializedAsync()
    {
        string apiData = await FetchDataFromAPI(); // Your API call
        StateService.DataFromAPI = apiData;
        StateService.NotifyStateChanged();
    }

    // ... your API call method ...
    private async Task<string> FetchDataFromAPI()
    {
        // Your API call logic here
        return await Task.FromResult("Data from API");
    }
}

4. Update the Main Razor Page:

In your main Razor page, display the data from the StateService. Blazor will automatically re-render this section when StateService.DataFromAPI changes because it's a property of a component.

@page "/"
@inject StateService StateService

<h1>Main Page</h1>
<p>@StateService.DataFromAPI</p>

<MySubComponent />

Important Considerations:

• Error Handling: Include proper error handling in your API calls within the sub-components.
• Complex State: For more complex applications, consider using a more sophisticated state management library like Fluxor or Redux.
• Asynchronous Operations: Ensure your API calls are handled asynchronously using async and await to prevent blocking the UI thread.

This pattern ensures that changes in any sub-component will trigger an update in the main page by updating the shared state and notifying the system of the change. The main page automatically re-renders because it's bound to the service's data. This avoids manual calls to StateHasChanged in the parent component, which is generally discouraged for this type of update.

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