Скачать или смотреть Understanding the Blazor Server Scoped Service Lifecycle: Why It Resets on Refresh

Explore why your Blazor Server scoped services initialize again upon page refresh, and discover effective approaches to maintain your application state.
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Understanding the Blazor Server Scoped Service Lifecycle: Why It Resets on Refresh

Blazor Server is a powerful framework for building interactive web applications. However, developers often encounter situations where they notice unexpected behavior, particularly regarding the lifecycle of services. One such issue arises when they find that scoped services, like a UserSettings service, seem to reset every time the page is refreshed. This guide aims to dissect this problem and offer practical solutions.

The Problem: Scoped Services Reset on Refresh

In a Blazor Server application, scoped services are tied to the user's session (or circuit). Here's a scenario to illustrate the issue:

You have a service, UserSettings, which generates a unique identifier (Id) upon initialization.

This service is injected into various components of your application.

When you switch between components, the Id remains consistent because they share the same instance of the service.

However, upon refreshing the webpage, the Id changes because a new instance of UserSettings is created.

The core of the problem lies in the lifecycle of scoped services. Each time you refresh the page, a new circuit gets instantiated, leading to the reinitialization of all scoped services.

Why Does This Happen?

Circuit Connections

Scoped Services: In Blazor Server, scoped services are created for each circuit. A circuit represents a user session, maintaining the state as long as the user interacts with the app.

Page Refresh: When you refresh the page, the current circuit is disposed of, and a new one is created. As a result, all scoped services, including UserSettings, are reinitialized.

Service Lifetimes in Blazor

Blazor offers several lifetimes for services:

Transient: Instances are created each time they are requested.

Scoped: Instances are created once per circuit connection.

Singleton: A single instance is shared throughout the app.

Using scoped services means they are not designed to persist across different circuit connections, thus leading to the unique Id being regenerated.

Proposed Solutions

To maintain a consistent Id across page refreshes, consider the following options:

1. Use AddSingleton

One straightforward approach is to change the service registration from AddScoped to AddSingleton. This will ensure that only one instance of UserSettings exists for the entire application.

Caution:

Shared State: If you go this route, be aware that this single instance will persist across all users. Therefore, if one user changes the Id, it will affect everyone using the service.

2. Store Id in Session or Local Storage

An alternative and more user-focused approach is to store the generated Id in the browser’s session storage or local storage. This method allows the Id to persist between refreshes without impacting other users.

Here’s a simple implementation:

Generate the Id on Initial Render: You can modify the UserSettings class to check for an existing Id in storage at initialization.

Use JavaScript Interop: Blazor provides JavaScript interop capabilities, enabling you to easily access and manipulate browser storage.

Example code snippet:

[[See Video to Reveal this Text or Code Snippet]]

Benefits of Using Storage

User Consistency: Each user’s Id stays consistent across refreshes.

Isolation of State: Changes in one user’s session won’t affect others.

Conclusion

Understanding the lifecycle of scoped services in Blazor Server is crucial for managing state effectively in your applications. Remember that the scoped lifetime ties the service to the user's current circuit. By adjusting your service lifetime or storing state in session or local storage, you can ensure a smoother user e