How to Download Files in Angular2 Using Observables and Blobs?

How Angular2 Handles File Downloading

In Angular2 and higher, downloading a file involves using Observables and Blobs to retrieve and save the data. Let's explore a specific scenario where an Angular application downloads a file.

Understanding the Problem

A user encounters an issue when implementing file download functionality in an Angular2 client for a WebApi/MVC app. They have the request set up correctly, but struggle with understanding how Angular manages file saving.

The Solution

The issue arises because the Observable that handles the file download runs in a separate context. This leads to an empty object being passed into the URL variable instead of the desired blob.

To address this, the solution involves subscribing to the Observable in a way that passes the data as a response directly to a designated function, such as:

this._reportService.getReport().subscribe(data => this.downloadFile(data));

Within the downloadFile function, the blob is created using the response data:

downloadFile(data: Response) {
  const blob = new Blob([data], { type: 'text/csv' });
  const url = window.URL.createObjectURL(blob);
  window.open(url);
}

By handling the subscription and blob creation separately, the correct context is established, ensuring that the URL variable contains the desired blob.

Additional Considerations

To ensure successful file opening, it is important to verify that 'rxjs/Rx' has been imported:

import 'rxjs/Rx';

This solution addresses the issue by properly handling the context in which the Observable and blob creation occur. It enables Angular2 applications to download files effectively.

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