What is FileResultin Asp.Net MVC? How to use FileResult in Asp.Net Core MVC?

 In ASP.NET MVC, the FileResult class is used to return a file to the client as the HTTP response. Here's an example of how to use FileResult in a controller action method:

csharp
public FileResult MyAction()
{
    // Get the file data
    var fileData = GetFileData();

    // Return the file as a FileResult
    return File(fileData, "application/pdf", "MyFile.pdf");
}

In this example, the MyAction method gets the file data and returns it as a FileResult using the File method. The File method takes three parameters: the file data as a byte array, the MIME type of the file, and the name of the file that the client should receive. The method returns a FileResult, which tells the MVC framework to send the file to the client as the HTTP response.

You can also use the File method to return files from the file system. Here's an example:

csharp
public FileResult MyAction()
{
    // Get the file path
    var filePath = Server.MapPath("~/Content/MyFile.pdf");

    // Return the file as a FileResult
    return File(filePath, "application/pdf", "MyFile.pdf");
}

In this example, the MyAction method gets the file path and returns the file as a FileResult using the File method. The File method takes the file path as the first parameter instead of the file data. The Server.MapPath method is used to map the virtual path "~/Content/MyFile.pdf" to the physical file path on the server.

You can also use the FileStreamResult class to return a file as a stream instead of a byte array. Here's an example:

csharp
public FileStreamResult MyAction()
{
    // Get the file stream
    var fileStream = GetFileStream();

    // Return the file stream as a FileStreamResult
    return new FileStreamResult(fileStream, "application/pdf");
}

In this example, the MyAction method gets the file stream and returns it as a FileStreamResult. The FileStreamResult constructor takes two parameters: the file stream and the MIME type of the file. The FileStreamResult class is useful when you want to return large files, as it allows you to return the file as a stream without loading the entire file into memory.