Скачать или смотреть How to Initialize a Service in Blazor WebAssembly at Startup

Learn how to efficiently initialize a service in Blazor WebAssembly using values from a Web API, ensuring your components leverage shared service data seamlessly.
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This video is based on the question https://stackoverflow.com/q/68941202/ asked by the user 'Jens Mander' ( https://stackoverflow.com/u/2367094/ ) and on the answer https://stackoverflow.com/a/68945419/ provided by the user 'Jens Mander' ( https://stackoverflow.com/u/2367094/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

If you're developing an application using Blazor WebAssembly, you might encounter a common challenge: how to initialize a shared service at startup using values retrieved from a Web API. This process is crucial, especially when multiple components rely on that service. The problem arises when the service appears uninitialized or differs from what’s expected when injected into your components.

In this guide, we’ll explore the steps to successfully initialize a service in Blazor WebAssembly, ensuring that it retains the necessary setup values across your application.

The Problem

You might find yourself in a situation where:

You have a service (Service A) that must be initialized with values obtained from a Web API.

You've attempted to set it up during the Program.cs file but encountered inconsistency when accessing these values from your components.

Attempts Made

Using AddScoped:

You added the service to the dependency injection container.

Attempted to initialize it using an asynchronous method to fetch setup values.

However, the injected service in your component returned a different instance.

Factory Method with AddScoped:

While trying to use a factory method to add the service, you ran into issues due to the asynchronous nature of fetching values from the Web API, leading to runtime errors.

The Solution

The good news is that this issue can be resolved by leveraging the lifecycle methods of your Blazor components. Instead of trying to initialize the service in the Program.cs, you'll handle it directly within the component that needs it.

Step-by-Step Implementation

Service Injection in Component
You'll need to inject needed services into your component by using the [Inject] attribute. This allows you to access other services along with Service A.

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Override OnInitializedAsync
Utilize the OnInitializedAsync lifecycle method to perform initialization when the component is ready.

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Accessing the Initialized Service
After the values have been set up in OnInitializedAsync, any components that inject Service A will have the correctly initialized instance.

Benefits of This Approach

Consistency: All components will work with the same initialized instance of Service A.

Asynchronous handling: You avoid runtime errors related to waiting on asynchronous calls during the service registration phase.

Cleaner structure: Initializing directly in your component keeps your logic encapsulated, making it easier to manage.

Conclusion

Initializing services in Blazor WebAssembly can be tricky, especially when dealing with asynchronous data from a Web API. However, by leveraging component lifecycle methods, you can ensure that your services are properly set up before they are utilized. This method not only resolves instance consistency issues but also embraces the power of asynchronous programming in Blazor.

If you have any questions or need further clarification on implementing this solution in your Blazor WebAssembly application, feel free to leave a comment below. Happy coding!