You're welcome 

Try

DataSet ds = (DataSet)((BindingSource)grid.DataSource).DataSource

1. [quote user="rajathan"]

thanks for the answer, but I got exception at    DataSet ds2 = (DataSet)datagrid1.datasource;

It said:"Unable to cast object of type 'System.Windows.Forms.BindingSource' to 'System.Data.DataSet'"

[/quote]

Please, provide the code for your initial databinding (probably it's not just  datagrid1.datasource=ds1;). Also, to be sure we're not too out-of-date: what version of NetAdvantage you use? (and is datagrid1 actually and UltraWinGrid control?)

 2.  [quote user="rajathan"]I have 2 ultragrid, A and B. what I want is: when I double click on one row in A, this row will be removed from A, and also that row will be removed from the dataset which is bound to A; mean while, I want to add this row to B, and that row will also be added to the dataset which is bound to B.[/quote]

Yes, this should (in general) work without any explicit refresh/update calls.

1. [quote user="rajathan"]//how to get the dataset from the datagrid??? [/quote] 

  DataSet ds2 = (DataSet)datagrid1.datasource;

 

2. [quote user="rajathan"]rebind the datagrid with the modified dataset.[/quote] 

In general you don't need to rebind the dataset (or need something else to update the grid). The grid should react to changes in the data source. This is the main concept of data binding. There are though some … small features in dataset events which should be taken into account. If your grid does not update itself after your operations with the dataset – post a message here. There are workarounds to make datagrid update itself (explicit calls).

1. DataTable.PrimaryKey is a unique property of the datatable (i.e. there is only one primary key, and that's all. The same concept is used in the databases BTW).

2. May be you meant UniqueConstraint http://msdn2.microsoft.com/en-us/library/system.data.uniqueconstraint.aspx ?

3. This are ADO.NET things. What does this have to do with Infragistics components?