How can I export a GridView.DataSource to a datatable or dataset?

Assuming your DataSource is of type DataTable, you can just do this:

myGridView.DataSource as DataTable

You should convert first DataSource in BindingSource, look example

BindingSource bs = (BindingSource)dgrid.DataSource; // Se convierte el DataSource 
DataTable tCxC = (DataTable) bs.DataSource;

With the data of tCxC you can do anything.

Personally I would go with:

DataTable tbl = Gridview1.DataSource as DataTable;

This would allow you to test for null as this results in either DataTable object or null. Casting it as a DataTable using (DataTable)Gridview1.DataSource would cause a crashing error in case the DataSource is actually a DataSet or even some kind of collection.

Supporting Documentation: MSDN Documentation on "as"

If you do gridview.bind() at:

if(!IsPostBack)

{

//your gridview bind code here...

}

Then you can use DataTable dt = Gridview1.DataSource as DataTable; in function to retrieve datatable.

But I bind the datatable to gridview when i click button, and recording to Microsoft document:

HTTP is a stateless protocol. This means that a Web server treats each HTTP request for a page as an independent request. The server retains no knowledge of variable values that were used during previous requests.

If you have same condition, then i will recommend you to use Session to persist the value.

Session["oldData"]=Gridview1.DataSource;

After that you can recall the value when the page postback again.

DataTable dt=(DataTable)Session["oldData"];

References: https://msdn.microsoft.com/en-us/library/ms178581(v=vs.110).aspx#Anchor_0

https://www.c-sharpcorner.com/UploadFile/225740/introduction-of-session-in-Asp-Net/