Answer/HowTo : Accessing columns collection via the private autoGenColumnsArray property in a DataGrid using AutoGenerate

[Jason Coyne Gaijin42]

I have seen several people looking for a way to access the Columns
collection when using the AutoGenerate = true option. Some
people have gotten so far as to find the private autoGenColumnsArray
that has the information, but we as developers have no way to access
this information.

I have come up with a solution for the problem, (as I am sure many
others have) using reflection. Here is some sample code that will
print out the auto generated column names from a datagrid.

As stated, this code uses reflection. Reflection is slow. It might not
also be allowed depending on your system's security settings. Also, if
MS changes the internal structure of the DataGrid, this might break.
(We are breaking encapsulation)

Provided, is a function that will generically allow you to get the
value of any private member of a class using reflection.

Sorry about the formatting, I dont know a good way to format code for
usenet. Visual Studio should clean up the code just find for you tho.

<code>
DataGrid dg = new DataGrid();
dg.DataSource =new DataTable();// (Run some query or whatnot here)
dg.DataBind

ArrayList AutoGeneratedColumns
= (ArrayList) GetPrivateField(dg,"autoGenColumnsArray") ;

if (AutoGeneratedColumns!= null)
foreach (DataGridColumn CurrentColumn in AutoGeneratedColumns)
{
Response.Write(CurrentColumn.HeaderText);
}
public static object GetPrivateField(object PassedObject, string
FieldName)
{

object Field=null;

if (PassedObject == null)
throw new ArgumentNullException("PassedObject"
,"PassedObject must be an instantiated object.");

if (FieldName == null || FieldName.Trim() == "")
throw new ArgumentOutOfRangeException("FieldName"
,"Fieldname must be a non empty string.");

Type ObjectType = PassedObject.GetType();
System.Reflection.FieldInfo PrivateField =
ObjectType.GetField(FieldName
,System.Reflection.BindingFlags.Instance
| System.Reflection.BindingFlags.NonPublic
| System.Reflection.BindingFlags.Public
| System.Reflection.BindingFlags.IgnoreCase);

if (PrivateField == null)
throw new ArgumentOutOfRangeException("FieldName"
, ObjectType.FullName + " does not have a field : " + FieldName +
".");

Field = PrivateField.GetValue(PassedObject);
return Field;
}
</code>