Скачать или смотреть Resolving Observable HttpEvent class Error in Angular 9

Discover how to fix the issue of Type 'Observable HttpEvent class ' not being assignable to type 'Observable class ' in your Angular 9 application with this detailed guide.
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This video is based on the question https://stackoverflow.com/q/62558685/ asked by the user 'indra257' ( https://stackoverflow.com/u/7582976/ ) and on the answer https://stackoverflow.com/a/62559504/ provided by the user 'Sergiu Molnar' ( https://stackoverflow.com/u/8916057/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving Observable<HttpEvent<class>> Error in Angular 9: A Comprehensive Guide

Developing applications with Angular can be exhilarating, but it sometimes brings unexpected challenges. One common issue developers encounter is related to Observable types, particularly the error message that states: Type 'Observable HttpEvent class ' is not assignable to type 'Observable class '. In this post, we will explore this problem and walk you through a step-by-step solution.

Understanding the Problem

In Angular, when making HTTP requests via services, we often use HttpClient to interact with APIs. In your application, you might have a service function designated to retrieve data based on specific user permissions. However, developers have reported running into the following error when using the options parameter in their HTTP GET method. The error message typically appears as:

Type 'Observable HttpEvent class ' is not assignable to type 'Observable class '.

Type 'HttpEvent' is not assignable to type 'ClassA'.

Type 'HttpSentEvent' has no properties in common with type 'ClassA'.

This is often a result of how the options object with headers is set up when making the HTTP call.

Analyzing Your Code

Let’s take a closer look at the relevant parts of your service code:

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

Here, you're attempting to make an HTTP GET request to retrieve data of type classA. However, due to the way the options are structured, TypeScript gets confused, thinking that it could be returning an Observable of type HttpEvent instead of your desired classA.

Step-by-Step Solution

To rectify this situation, here are the detailed changes you should implement:

Step 1: Correct Your HTTP GET Call

Modify your getSelectedPractitionerPermissions method to ensure that it explicitly specifies the headers. Update the return statement as follows:

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

By doing this, you're telling TypeScript that the options parameter is being passed as an object containing headers, preventing it from defaulting to an HttpEvent.

Step 2: Ensure getAuthInfo Returns Correctly

In your getAuthInfo method, make sure it returns correctly constructed headers without being wrapped in an unnecessary object. Your method could remain as:

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

Conclusion

By following the above adjustments, you should be able to resolve the type error in your Angular application while keeping the authentication headers for your API requests intact. Type safety is one of the strengths of TypeScript, and ensuring accuracy in your method signatures leads to fewer runtime errors.

Additional Tips

Always ensure that your models or classes (classA in this case) have the same properties you expect from the API response.

Use Angular’s built-in HTTP interceptors for handling authentication and error responses in a more global manner, which can help streamline your service layer.

Tackling type issues in Angular can seem daunting, but by making small adjustments and being aware of TypeScript's expectations, you can smoothly navigate these challenges. Happy coding!