A DataTable
represents a table of a dataset. DataTable provides many events that an
application can track down (see Table 01).
Table 01. The
DataTable Events
|
EVENT
|
DESCRIPTION
|
|
ColumnChanged
|
This event occurs when a value of a column has been changed.
|
|
ColumnChanging
|
This event occurs when a new value is being added to a column.
|
|
RowChanged
|
This event occurs when a value of a row in the table has been
changed.
|
|
RowChanging
|
This event occurs when a row in a table has been changed.
|
|
RowDeleted
|
This event occurs when a row in a table has been deleted.
|
|
RowDeleting
|
This event occurs when a row is being deleted.
|
ColumnChangedEventHandler handles the
ColumnChanged event; it's as follows:
public delegate void DataColumnChangeEventHandler(object sender, DataColumnChangeEventArgs e);
Where sender is the source of
the event and e is DataColumnChangedEventArgs, which contains the event data.
ColumnChangingEventHandler
handles the ColumnChanging Event; it's as follows:
public delegate void DataColumnChangeEventHandler(object sender,DataColumnChangeEventArgs e);
Where Sender is the source of
the event and e is DataColumnChangingEventArgs, which contains the event data.
Similarly, to these two handlers,
RowChangedEventHandler, RowChangingEventHandler, RowDeletingEventHandler, and
RowDeletedEventHandler handle the RowChanged, RowChanging, RowDeleting, and
RowDeleted events, respectively. Definitions of these event handlers are
similar to DataColumnChangingEventHandler and DataColumnChangedEventHandler.
To test these I'll create a data
table, add data rows to the table, and then update and delete rows from the
table.
Listing 9-8 creates a data
table, adds three columns (id, name, and address), adds data to the table, and
changes the columns of the table. It also calls the ColumnChanged and
ColumnChanging event handlers. You write the code for the ColumnChanged and
ColumnChanging event handlers in the Column_Changed and Column_Changing
methods. Specifically, you can write this code on a button-click event handler.
Listing 9-8.
Writing the Column and ColumnChanged event handlers
private void ColumnChange_Click(object sender,
System.EventArgs e)
{
DataTable custTable = new DataTable("Customers");
// add columns
custTable.Columns.Add("id", typeof(int));
custTable.Columns.Add("name", typeof(string));
custTable.Columns.Add("address", typeof(string));
// Add ColumnChanging and ColumnChanged event handlers
custTable.ColumnChanging += new DataColumnChangeEventHandler(Column_Changing);
custTable.ColumnChanged += new DataColumnChangeEventHandler(Column_Changed);
// add Two rows
custTable.Rows.Add(new object[] { 1, "name1", "address1" });
custTable.Rows.Add(new object[] { 2, "name2", "address2" });
custTable.AcceptChanges();
// Change the name column in all the rows
foreach (DataRow row in custTable.Rows)
{
row["name"] = "new
name";
}
}
private static void Column_Changed(object sender, DataColumnChangeEventArgs e)
{
MessageBox.Show("Column_changed Event: " + " ,
" +
e.Row["name"] + " ," +
e.Column.ColumnName + ", " +
e.Row["name", DataRowVersion.Original]);
}
private static void Column_Changing(object sender, DataColumnChangeEventArgs e)
{
MessageBox.Show("Column_changing Event: " + " ,
" +
e.Row["name"] + " ," +
e.Column.ColumnName + ", " +
e.Row["name", DataRowVersion.Original]);
}
Listing 9-9 creates a data
table, adds three columns (id, name, and address), adds data to the table, and
changes the columns of the table. It also calls the RowChanging and RowChanged
event handlers.
Listing 9-9.
Writing the RowChanging and RowChanged event handlers
private void UpdateRow_Click(object sender,
System.EventArgs e)
{
DataTable custTable = new DataTable("Customers");
// add columns
custTable.Columns.Add();
custTable.Columns.Add("id", typeof(int));
custTable.Columns.Add("name", typeof(string));
custTable.Columns.Add("address", typeof(string));
// add Two rows
custTable.Rows.Add(new object[] { 1, "name1", "address1" });
custTable.Rows.Add( new object[] { 2, "name2", "address2" });
custTable.AcceptChanges();
foreach (DataRow row in custTable.Rows)
{
row["name"] = "new
name";
// Adding
RowChanged and RowChanging event handlers
custTable.RowChanged += new DataRowChangeEventHandler(Row_Changed);
custTable.RowChanging += new DataRowChangeEventHandler(Row_Changing);
}
}
private static void Row_Changed (object sender, DataRowChangeEventArgs e)
{
MessageBox.Show("Row_Changed Event:" +
e.Row["name", DataRowVersion.Original].ToString()
+
e.Action.ToString());
}
private static void Row_Changing(object sender, DataRowChangeEventArgs e)
{
MessageBox.Show("Row_Changing Event:" +
e.Row["name", DataRowVersion.Original].ToString()
+
e.Action.ToString());
}
Listing 9-10 creates a data
table, adds three columns (id, name, and address), adds data to the table, and
changes the columns of the table. It also calls the RowDeleting and RowDeleted
event handlers.
Listing 9-10.
Writing the RowDeleting and RowDeleted event handlers
private void DeleteRow_Click(object sender,
System.EventArgs e)
{
DataTable custTable = new DataTable("Customers");
// add columns
custTable.Columns.Add();
custTable.Columns.Add("id", typeof(int));
custTable.Columns.Add("name", typeof(string));
custTable.Columns.Add("address", typeof(string));
// Add RowDeleting and RowDeleted events
custTable.RowDeleting += new DataRowChangeEventHandler(Row_Deleting);
custTable.RowDeleted += new DataRowChangeEventHandler(Row_Deleted);
// add Two rows
custTable.Rows.Add(new object[] { 1, "name1", "address1" });
custTable.Rows.Add(new object[] { 2, "name2", "address2" });
custTable.AcceptChanges();
//Delete all the rows
foreach (DataRow row in custTable.Rows)
row.Delete();
}
private static void Row_Deleting(object sender, DataRowChangeEventArgs e)
{
MessageBox.Show("Row_ Deleting Event:" +e.Row["name", DataRowVersion.Original].ToString()
+e.Action.ToString());
}
private static void Row_Deleted (object sender, DataRowChangeEventArgs e)
{
MessageBox.Show("Row_Deleted Event:" + e.Row["name", DataRowVersion.Original].ToString()
+ e.Action.ToString());
}
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