FileSelect Stream throws NotImplementedException

Environment

Description

The file.Stream object in the FileSelect OnSelect event handler throws a NotImplementedException.

The FileSelect Stream (FileInfoStream) has exposed methods that are "not implemented".

Error Message

System.NotImplementedException: The method or operation is not implemented.
    at Telerik.Blazor.Components.FileSelect.Stream.FileInfoStream.Read()

The same exception will occur for the following methods and properties:

• Position
• Flush()
• Read()
• Seek()
• SetLength()
• Write()

Possible Cause

Due to Blazor framework limitations, FileInfoStream does not support synchronous operations such as Read, Seek, Flush and Write. The methods exist, but throw an exception.

Solution

Copy the FileInfoStream asynchronously to another Stream via CopyToAsync(). Apart from the example below, also check the FileSelect OnSelect event documentation.

Copy the FileSelect Stream to another one and use sync methods

@using System.IO

<TelerikFileSelect OnSelect="@ReadSelectedFiles" />

@code {
    private async Task ReadSelectedFiles(FileSelectEventArgs args)
    {
        foreach (var file in args.Files)
        {
            var ms = new MemoryStream();
            await file.Stream.CopyToAsync(ms);

            var byteArray = new byte[file.Size];

            ms.Seek(0, SeekOrigin.Begin); // not supported by file.Stream
            ms.Read(byteArray); // not supported by file.Stream
        }
    }
}

See Also

• FileSelect Overview