a delegate problem over 2 projects in 1 solution

Question

5.00/5 (1 vote)

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Hello Friends,

I have the next problem.
I have a project (DBConnecting.DataObjects.DataObjects) that is the communication between my windows form app and my Sql Server 2008 Database.

In my 2nd project: a Windows form (that references DBConnecting.DataObjects.DataObjects) that calls the Async table method to load a datatable object asynchronous.

C#

string query = "select * from [dbo].[FactInternetSales]";
            DBConnecting.DataObjects.DataObjects.AsyncDataTableStart(query, null, CommandType.Text, null);

In the DBConnecting project the AsyncDataTableStart gets called and this method calls the method GetAsyncDataTableEnd

C#

public static IAsyncResult AsyncDataTableStart(String Query, List<sqlparameter> sqlParameters, CommandType sqlCommandType, String ConnectionString)
        {
            SqlCommand command = Open(Query, sqlParameters, sqlCommandType, ConnectionString);
            return command.BeginExecuteReader(GetAsyncDataTableEnd, command, CommandBehavior.CloseConnection);
        }

        public static void GetAsyncDataTableEnd(IAsyncResult myResult)
        {
            SqlCommand command = null;
            SqlDataReader dr = null;
            
            DateTime nu = DateTime.Now;
            DataTable myTable = new DataTable();
            try
            {
                command = (SqlCommand)myResult.AsyncState;
                dr = command.EndExecuteReader(myResult);
                myTable.Load(dr);
                
            }
            catch
            {
            }
            finally
            {
                if (dr != null)
                    dr.Close();
                if (command != null && command.Connection.State != ConnectionState.Closed)
                    command.Connection.Close();
            }
        }
</sqlparameter>

So I have a DataTable object loaded with data, but How do I return this table to the windowsform?
In the DBConnecting.DataObjects.DataObjects class I would like to have a delegate that when the windows form implements this delegate the datatable is returned so it can be set as DataSource for a DataGridView.

Please help me with some examples

Posted 19-Aug-11 4:38am

Herman<T>.Instance

Updated 19-Aug-11 4:44am

v2

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Philippe Mori 19-Aug-11 16:12pm

Having 2 projects does not matters much... as long as type like a delegate that are used by both are declared in the first project.

1 solution

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Shameel · Accepted Answer · 2011-08-19T04:52:00

Solution 1

This[^] article contains information on how to pass information back using IAsyncResult.

Create the DataTableEventArgs in your source project

C#

public class DataTableEventArgs : System.EventArgs {
    DataTable dataTable;
    public DataTable DataTableInfo {
        get {
            return dataTable;
        }
    }

    public DataTableEventArgs(DataTable dataTable) {
        this.dataTable= dataTable;
    }
}

Declare the delegate in your source project

C#

public delegate void DataTableEventHandler(object sender, DataTableEventArgs e);

Declare the event in the class that returns the DataTable

C#

public event DataTableEventHandler ReturnDataTable;

Raise the event where you want to send the DataTable

C#

if (ReturnDataTable != null) {
    DataTable dataTable = BuildDataTable();
    ReturnDataTable(this, dataTable);
}

Now, in your receiver class that must receive the DataTable

C#

private void Init() {
    //Bind your method to the event
    MyDataSource src = new MyDataSource();
    src.ReturnDataTable += new DataTableEventHandler(HandleDataTable);
}

private void HandleDataTable(object sender, DataTableEventArgs e) {
    DataTable dataTable = e.DataTableInfo;
    //Use dataTable here
}

Posted 19-Aug-11 4:52am

Shameel

Updated 19-Aug-11 9:24am

v2

Comments

Herman<T>.Instance 19-Aug-11 11:00am

my current declaration of the delegate looks like:
public delegate DataTable ReturnTable(DataTable theTable);

how should I do this (sorry no experience with delegates)

[no name] 19-Aug-11 15:24pm

See my updated answer.

Herman<T>.Instance 19-Aug-11 16:05pm

I am gonna try this on monday and if it works I'll take a deep bow for you

Herman<T>.Instance 20-Aug-11 7:58am

it fails on ReturnDataTable(this, dataTable);
Error 2 Argument 2: cannot convert from 'System.Data.DataTable' to 'DBConnecting.EventHandlers.DataTableEventArgs'

my source:

public void GetAsyncDataTableEnd(IAsyncResult myResult)
{
SqlCommand command = null;
SqlDataReader dr = null;

DateTime nu = DateTime.Now;
DataTable myTable = new DataTable();
try
{
command = (SqlCommand)myResult.AsyncState;
dr = command.EndExecuteReader(myResult);
if (ReturnDataTable != null)
{
myTable.Load(dr);
ReturnDataTable(this, myTable);
}
}
catch
{
}
finally
{
if (dr != null)
dr.Close();
Close(command);
}
}

(need full project to see what I have done?)

[no name] 20-Aug-11 14:14pm

Do this:
DataTableEventArgs dtArgs = new DataTableEventArgs(myTable);
ReturnDataTable(this, dtArgs);

Herman<T>.Instance 21-Aug-11 13:27pm

yes that works and the table is fully received in the HandleDataTable(object sender, DataTableEventArgs e) method. But when I set gridView1.DataSource = e.DataTableInfo; the gridview is not showing any data....

[no name] 21-Aug-11 14:10pm

Before binding the data table to the GridView, check if the DataTable has any rows and if the rows contain data:
int rowCount = dataTable.Rows.Count;
string data = dataTable.Rows[0].Columns[0].ToString();

Herman<T>.Instance 22-Aug-11 4:04am

it has al 60,000 rows

Herman<T>.Instance 22-Aug-11 4:41am

my code:
private void HandleDataTable(object sender, DataTableEventArgs e)
{
DataTable table = e.DataTableInfo;
dataGridView1.DataSource = table;
toolStripStatusLabel1.Text = "Finished Async Call";
}

and even the 'toolStripStatusLabel1' is not updated

Herman<T>.Instance 22-Aug-11 4:55am

I caught a famous exception while debugging:
Cross-thread operation not valid: Control 'dataGridView1' accessed from a thread other than the thread it was created on.

[no name] 22-Aug-11 15:05pm

Hello, Sorry for the late reply. I do not have email access at my workplace and so could not see your comments.
I see that you have fixed the bug, that's great. It was a cross thread exception. You need to check InvokeRequired and call Invoke. Since you are going to always populate the grid from the Async call, InvokeRequired is not necessary.

Herman<T>.Instance 22-Aug-11 5:10am

fixed the error with the next code:

private void HandleDataTable(object sender, DataTableEventArgs e)
{

DataTable table = e.DataTableInfo;
updateGridViewDelegate updDel = new updateGridViewDelegate(updateGridView);
object[] arg = new object[1];
arg[0] = e.DataTableInfo;
dataGridView1.Invoke(updDel, arg);
toolStripStatusLabel1.Text = "Finished Async Call";
}

private void updateGridView(DataTable aTable)
{
dataGridView1.DataSource = aTable;
}

Herman<T>.Instance 19-Aug-11 11:06am

Your solution has the grid, the delegate and the async method in 1 class. I have it in separate classes and projects!

I like the document, let that be clear

Philippe Mori 19-Aug-11 16:09pm

By experience, when you add an event handler explicitly, you should also remove it explicitly (in the receiver class, typically in Dispose method).

Herman<T>.Instance 19-Aug-11 16:11pm

thanks for the advice. I'll keep it in mind