Writing more than 1Kb to a MemoryStream

owain · November 4th, 2004, 09:03 AM

I have written a routine that accepts as a parameter a System.IO.TextWriter, this is then used to create a System.Xml.XmlTextWriter and I proceed to write some Xml content to the stream using the XmlTextWriter. When I pass in a System.IO.StringWriter this works well and I can display the Xml content.

I now want to encrypt the Xml, therefore I have created a System.IO.MemoryStream, then I use this to create a System.IO.StreamWriter which I pass into my routine that creates the Xml. The problem is that only 1024 bytes (1Kb) seem to be written to the stream. I have tried creating the stream with a capacity of 102400 (100Kb) however only 1Kb is written. I have also tried setting the length of the stream to 100Kb, still only 1Kb is written and the 1025th byte in the stream is 0.

Here is a quick example of my code:

Code:

    ' Create a MemoryStream with a capacity of 100Kb
    Dim myStream As New MemoryStream(102400)
    ' Use this MemoryStream to create a StreamWriter
    Dim myWriter As New StreamWriter(myStream)

    ' Call the MakeXml routine and pass in the StreamWriter
    MakeXml(myWriter)

    ' Use the MemoryStream to create a StreamReader
    Dim myReader As New StreamReader(myStream)

    ' Read to the end of the StreamReader placing the data into a text box
    Text1.Text = myReader.ReadToEnd

And here is an example of the code in the MakeXml() routine:

Code:

Public Sub MakeXml(ByRef s As TextWriter)

Code:

    Dim XmlWriter As New System.Xml.XmlTextWriter(s)

    With XmlWriter
        .WriteStartDocument()
        .WriteStartElement("Book")
        .WriteAttributeString("Title", "Pro VB.NET")

        ' Lots more calls to write some Xml content...

        .WriteEndElement()
        .WriteEndDocument()
    End With

End Sub

What do I have to do to write more than 1Kb to the MemoryStream? What am I doing wrong?

Regards
Owain Williams

owain · November 4th, 2004, 09:59 AM

OK, it is just me being stupid, I have found the answer. Before I continue there was a mistake in the code I posted made when simplifying my actual code, I forgot to state that I set the position of the MemoryStream (the variable myStream) to 0 (myStream.Position = 0) before declaring the StreamReader.

Anyway, I fixed it by flushing the XmlTextWriter before returning from the MakeXml routine, here is my code again, this time working!:

Code:

    ' Create a MemoryStream with a capacity of 100Kb
    Dim myStream As New MemoryStream(102400)
    ' Use this MemoryStream to create a StreamWriter
    Dim myWriter As New StreamWriter(myStream)

    ' Call the MakeXml routine and pass in the StreamWriter
    MakeXml(myWriter)

    ' Position the MemoryStream at the start before creating the StreamReader
    myStream.Position = 0

    ' Use the MemoryStream to create a StreamReader
    Dim myReader As New StreamReader(myStream)

    ' Read to the end of the StreamReader placing the data into a text box
    Text1.Text = myReader.ReadToEnd

Here is the fixed MakeXml() routine:

Code:

Public Sub MakeXml(ByRef s As TextWriter)

Code:

    Dim XmlWriter As New System.Xml.XmlTextWriter(s)

    With XmlWriter
        .WriteStartDocument()
        .WriteStartElement("Book")
        .WriteAttributeString("Title", "Pro VB.NET")

        ' Lots more calls to write some Xml content...

        .WriteEndElement()
        .WriteEndDocument()
        ' Don't forget to Flush the stream before exiting the routine!
        .Flush()
    End With

End Sub

And that was all I needed to do.

D'oh :)

Regards
Owain Williams