(sql or oledb)command--(by executereader等)-->datareader---->datagrid
(sql or oledb)dataadapter--(by fill(datasetname)等)-->dataset---->datagrid
The ADO.NET DataReader object is designed to be a server-side, forward-only, read-only cursor. The ADO.NET DataSet object is a disconnected storage tool for rowsets. It stores records without holding a connection to a data source and, in fact, it does not care from what data source its rowsets are derived. The DataSet is a binary object when stored in memory, but it can also be serialized easily to and from XML. It is similar to the ADO Recordset object with its CursorType set to adOpenStatic and CursorLocation set to adUseClient, when it has been disconnected from its associated Connection object (via the Recordset's ActiveConnection property). The ADO.NET DataAdapter object is a bridge between the connection and DataSet objects. It can load a DataSet from a data source using a connection and it can update a data source with the changes stored in a DataSet. The behavior of the ADO Recordset depends on its property settings (including the CursorType and CursorLocation properties). In ADO.NET there are separate objects built to handle these specific situations instead of requiring one object to fit all scenarios.