XmlReader Question

[CGuy]

Hi,

I am using an XmlTextReader to read an xml file. It may happen that the
file is present in the disk, but it may be empty (0 bytes). I would like to
find out whether the xml file contains a valid root node or not. How do I do
this?

This is what I need
if(File.Exists( fileName))
{
XmlTextReader xmReader = new XmlTextReader(f ileName);
//How do I find out whether this xml document contains a Root node named
"ROOT_NODE" or not?
}

CGuy

[Christoph Schittko [MVP]]

You can loop with the reader through the document until you find the first
element node and then check if node's name is not ROOT_NODE. The code goes
something like this:

while( ( true == xmlReader.Read( ) )
&& ( XmlNodeType.Ele ment != xmlReader.NodeT ype ) ) {}

// now we're at the first element node and can check the name:
if( "ROOT_NODE" == xmlReader.Name )
{
// it is ...
}
else
{
// it isn't
}

--
HTH
Christoph Schittko [MVP]
Software Architect, .NET Mentor
"CGuy" <cg**@csharp.ne t> wrote in message
news:uq******** ******@tk2msftn gp13.phx.gbl...

Hi,

I am using an XmlTextReader to read an xml file. It may happen that the file is present in the disk, but it may be empty (0 bytes). I would like to find out whether the xml file contains a valid root node or not. How do I do this?

This is what I need
if(File.Exists( fileName))
{
XmlTextReader xmReader = new XmlTextReader(f ileName);
//How do I find out whether this xml document contains a Root node named "ROOT_NODE" or not?
}

CGuy

[Christoph Schittko [MVP]]

I don't know about any way to avoid the exception, but could you help me
understand what's bad about the exception? Does the exception not contain
enough information for you? Is "no root element" the same state as "empty
file" or do you need to treat them separately? You can easily do both by
handling the exception correctly, but I'd like to understand before I post
more samples.

--
HTH
Christoph Schittko [MVP]
Software Architect, .NET Mentor

"CGuy" <cg**@csharp.ne t> wrote in message
news:eK******** ******@tk2msftn gp13.phx.gbl...

Hi Christoph,

Thanks for your comments. But this doesn't solve my problem - it may
happen that the XML file I'm processing may exist in the harddrive, but with no data (0 bytes - due to some error in the previous run). So, when I do
while( ( true == xmlReader.Read( ) ) && ( XmlNodeType.Ele ment !=
xmlReader.NodeT ype ) ), C# compiler throws an XmlException - "root element
not present". How do I do this without getting this exception?

CGuy
"Christoph Schittko [MVP]" <ch************ ********@austin .rr.com> wrote in
message news:uF******** ******@TK2MSFTN GP10.phx.gbl...

You can loop with the reader through the document until you find the first element node and then check if node's name is not ROOT_NODE. The code goes something like this:

while( ( true == xmlReader.Read( ) )
&& ( XmlNodeType.Ele ment != xmlReader.NodeT ype ) ) {}

// now we're at the first element node and can check the name:
if( "ROOT_NODE" == xmlReader.Name )
{
// it is ...
}
else
{
// it isn't
}

--
HTH
Christoph Schittko [MVP]
Software Architect, .NET Mentor
"CGuy" <cg**@csharp.ne t> wrote in message
news:uq******** ******@tk2msftn gp13.phx.gbl...

Hi,

I am using an XmlTextReader to read an xml file. It may happen

that the

file is present in the disk, but it may be empty (0 bytes). I would

like to

find out whether the xml file contains a valid root node or not. How

do I

do

this?

This is what I need
if(File.Exists( fileName))
{
XmlTextReader xmReader = new XmlTextReader(f ileName);
//How do I find out whether this xml document contains a Root node

named

"ROOT_NODE" or not?
}

CGuy

[CGuy]

Hi Christoph,

I wanted to avoid the exception because I wanted to avoid nested
try-catch blocks (In the code, I have 2 outer levels tray-catch blocks).
Anyway, I have followed your approach and everything works fine. This is how
I have done it

try
{
//Initialize XmlTextWriter
try
{
XmlTextReader xmReader = new XmlTextReader(s tream);
while(xmReader. Read() == true)
{
if(xmReader.Nod eType == XmlNodeType.Ele ment && xmReader.Name ==
"ROOT_NODES ")
{
//Has root node
break;
}
}
}
catch(XmlExcept ion)
{
xmWriter.WriteS tartDocument();
xmWriter.WriteS tartElement("RO OT_NODE");
}
}
finally
{
//Writer the Header for current session
}
}
catch()
{
...
}
Thanks again
CGuy
"Christoph Schittko [MVP]" <ch************ ********@austin .rr.com> wrote in
message news:ev******** ******@TK2MSFTN GP12.phx.gbl...

I don't know about any way to avoid the exception, but could you help me
understand what's bad about the exception? Does the exception not contain
enough information for you? Is "no root element" the same state as "empty
file" or do you need to treat them separately? You can easily do both by
handling the exception correctly, but I'd like to understand before I post
more samples.

--
HTH
Christoph Schittko [MVP]
Software Architect, .NET Mentor

"CGuy" <cg**@csharp.ne t> wrote in message
news:eK******** ******@tk2msftn gp13.phx.gbl...

Hi Christoph,

Thanks for your comments. But this doesn't solve my problem - it may
happen that the XML file I'm processing may exist in the harddrive, but

with

no data (0 bytes - due to some error in the previous run). So, when I do
while( ( true == xmlReader.Read( ) ) && ( XmlNodeType.Ele ment !=
xmlReader.NodeT ype ) ), C# compiler throws an XmlException - "root element

not present". How do I do this without getting this exception?

CGuy
"Christoph Schittko [MVP]" <ch************ ********@austin .rr.com> wrote in message news:uF******** ******@TK2MSFTN GP10.phx.gbl...

You can loop with the reader through the document until you find the

first element node and then check if node's name is not ROOT_NODE. The code goes something like this:

while( ( true == xmlReader.Read( ) )
&& ( XmlNodeType.Ele ment != xmlReader.NodeT ype ) ) {}

// now we're at the first element node and can check the name:
if( "ROOT_NODE" == xmlReader.Name )
{
// it is ...
}
else
{
// it isn't
}

--
HTH
Christoph Schittko [MVP]
Software Architect, .NET Mentor
"CGuy" <cg**@csharp.ne t> wrote in message
news:uq******** ******@tk2msftn gp13.phx.gbl...
> Hi,
>
> I am using an XmlTextReader to read an xml file. It may happen that the
> file is present in the disk, but it may be empty (0 bytes). I would like to
> find out whether the xml file contains a valid root node or not. How

do

I

do
> this?
>
> This is what I need
> if(File.Exists( fileName))
> {
> XmlTextReader xmReader = new XmlTextReader(f ileName);
> //How do I find out whether this xml document contains a Root node named
> "ROOT_NODE" or not?
> }
>
> CGuy
>
>