How to return Datatable using [WebMethod]

Question

I have a web service that should return the top 5 letters in my mailbox and display them in the data grid. At first I put my data in a DataTable . But keep getting errors

Here is my code: did I miss something or proclaim something is wrong?

 [WebMethod] public DataTable DisplayMailList(String inMailServer, String inPort, bool inSSlCheck, String inUsername, String inPassword) { objClient.Connect(inMailServer, int.Parse(inPort), inSSlCheck); objClient.Authenticate(inUsername, inPassword); int count = objClient.GetMessageCount(); DataTable dtMessages = new DataTable(); // Creating datatable. dtMessages.Columns.Add("MessageNumber"); dtMessages.Columns.Add("From"); dtMessages.Columns.Add("Subject"); dtMessages.Columns.Add("DateSent"); dtMessages.TableName = "dtMessages"; int counter = 0; for (int i = count; i >= 1; i--) { OpenPop.Mime.Message msg = objClient.GetMessage(i); dtMessages.Rows.Add(); dtMessages.Rows[dtMessages.Rows.Count - 1]["MessageNumber"] = i; //Populateing Datatable dtMessages.Rows[dtMessages.Rows.Count - 1]["Subject"] = msg.Headers.Subject; dtMessages.Rows[dtMessages.Rows.Count - 1]["DateSent"] = msg.Headers.DateSent; counter++; if (counter > 5) { break; } } return dtMessages; } 

Think of the issue as a publicly accessible DataTable . I declared it as an object, but it did not work on the air ... sigh, what should I declare as? this is mistake....

Fix System.InvalidOperationException: An error occurred that generated the XML document. ---> System.InvalidOperationException: DataTable cannot be serialized. The name DataTable is not set.

Answer 1

Assigning a dtMessages.DataTable value dtMessages.DataTable stop the serialization error, as the error message indicates.

  [WebMethod] public DataTable GetDataTable() { DataTable dt = new DataTable(); dt.Columns.Add("Col1", typeof(string)); dt.Rows.Add("testing"); dt.TableName = "Blah"; // <--- return dt; } 

But I agree with Bob Horn that you better define a class for the return value than use a DataTable.

Answer 2

Just provide the table name when creating the data object

 DataTable dt = new DataTable("tablename"); 

Answer 3

This worked for me:

In your application

  public void app() { try { DataTable dtInput = new DataTable(); DataRow drRow; dtInput.Columns.Add("ID"); dtInput.Columns.Add("Name"); drRow = dtInput.NewRow(); drRow["ID"] = 1; drRow["Name"] = "Star"; dtInput.Rows.Add(drRow); dtInput.TableName = "Input";//Table name is mandatory to avoid serialization exception DataTable dtOutput = new DataTable(); dtOutput.TableName = "Output";//Table name is mandatory to avoid serialization exception service.TestService(dtInput ,ref dtOutput); } catch (Exception ex) { } } 

In your service

  DataTable dtOutput= new DataTable(); [WebMethod] public void TestService(DataTable dtInput , ref DataTable dtOutput) { DataRow drRow; drRow= dtInput.NewRow(); drRow["ID"] = 2; drRow["Name"] = "Success"; dtInput.Rows.Add(drRow); dtOutput= dtInput; } 

Answer 4

Hey brother, I want to know how you are debugging your method with dates.

here

[WebMethod] public DataTable DisplayMailList (String inMailServer, String inPort, bool inSSlCheck, String inUsername, String inPassword) {
objClient.Connect (inMailServer, int.Parse (inPort), inSSlCheck); objClient.Authenticate (inUsername, inPassword);