In VB.Net, which file stream accept Seek end Peek methods?

Question

I recently read on Setting position index of filestream that it is possible to use seek() method of BaseStream class.

But now, using .Net Framework 4.8 or greater these 2 functions seem to have been deleted.

Which stream in .Net 4.8 or greater does implement this 2 functions ?

I search a solution that is distinct from My.MyComputer.SystemFile.Seek() and is not restricted to using old VB 6 FileOpen() method !

Answer 1

The System.IO.FileStream class inherits the System.IO.Stream class. The latter provides the base functionality for all streams while the former provides functionality for streams backed by files. The Seek method is a member of the Stream class and thus every stream, regardless of type, has that method. That's true up to .NET 6 and will continue to be true as long as .NET exists.

The Seek method might throw a NotSupportedException in some cases, in which case the CanSeek property of that stream will be False. If you have a stream and you're not sure whether it can seek or not, test that property before calling Seek to ensure no exception will be thrown. In the case of a FileStream, the documentation (which you should already have read) tells us when to expect that property to be False:

true if the stream supports seeking; false if the stream is closed or if the FileStream was constructed from an operating-system handle such as a pipe or output to the console.

You can read the documentation of other types of streams to see whether they support seeking, e.g. MemoryStream does and NetworkStream doesn't. Basically, seeking requires random access to all the data rather than just sequential access.

There is no BaseStream property on a FileStream. The property you refer to is a member of StreamReader class. That property will return a Stream reference to the stream being read. That could be a FileStream, NetworkStream, MemoryStream or whatever. If you have a StreamReader and you want to seek to a specific position in the underlying stream but you don't know whether it is supported or not then you get the BaseStream, test the CanSeek property and, if it's True, call the Seek method.

With myStreamReader.BaseStream
    If .CanSeek Then
        'Advance the file pointer 64 bytes.
        .Seek(64L, SeekOrigin.Current)
    End If
End With

That will work no matter what type of stream backs the reader because CanSeek and Seek are members of Stream and StreamReader.BaseStream is type Stream.