DataTable Events

  • Thread starter Thread starter Aart Hoevenberg
  • Start date Start date
A

Aart Hoevenberg

What is the difference (in usage) of the datatable events ColumnChanged and
ColumnChanging (the same applies to the rowchanged and row changing and
rowdeleted and rowdeleting)? It looks to me that one of the events:
ColumnChanged or ColumnChanging would suffice.
 
Hi Miha,

Both events (changing and changed) fire when changing a column in code. What
happens between those events? What could be a good usage for placing code in
the changing event or the changed event?

Thanks

Miha Markic said:
Hi Aart,

Changing occurs before the data is actually changed...

--
Miha Markic [MVP C#] - RightHand .NET consulting & development
miha at rthand com
www.rthand.com

Aart Hoevenberg said:
What is the difference (in usage) of the datatable events ColumnChanged
and ColumnChanging (the same applies to the rowchanged and row changing
and rowdeleted and rowdeleting)? It looks to me that one of the events:
ColumnChanged or ColumnChanging would suffice.
Click to expand...
Click to expand...
 
Hi Aart,

Aart Hoevenberg said:
Hi Miha,

Both events (changing and changed) fire when changing a column in code.
Click to expand...

Yes, but changing fires *before* the value is changed while changed fires
*after* it is changed.

What
happens between those events? What could be a good usage for placing code
in the changing event or the changed event?
Click to expand...

That depends on you. If you need it you can use it, otherwise don't :-)
(for example, you might have to execute some code before the data is
changed, or set a flag, etc. - you would use changing)
 
U¿ytkownik "Aart Hoevenberg said:
Hi Miha,

Both events (changing and changed) fire when changing a column in code.
What happens between those events? What could be a good usage for placing
code in the changing event or the changed event?

Thanks
Click to expand...

If you throw exception in changing event you can retire changes. Changed
events you can use to make changes in other tables but you can't (in simple
way) resign.
For example:

using System;
using System.Data;

namespace chngDtEvent
{
class Class1
{
[STAThread]
static void Main(string[] args)
{
test myT = new test();
myT.AddSomeData();
myT.ListPersons();
System.Console.ReadLine();
}
}
public class test
{
private DataTable myDt = new DataTable("myT");

public test()
{
//column definition
DataColumn dc = new DataColumn("Name",
System.Type.GetType("System.String"));
myDt.Columns.Add(dc);

//events definitions
myDt.RowChanging +=
new DataRowChangeEventHandler(myDt_RowChanging);
myDt.RowChanged +=
new DataRowChangeEventHandler(myDt_RowChanged);
}
public void AddSomeData()
{
AddOnePerson("Ben");
AddOnePerson("Bill");
AddOnePerson("George");
}

public void AddOnePerson(string name)
{
try
{
DataRow myDr = myDt.NewRow();
myDr["Name"] = name;
myDt.Rows.Add(myDr);
}
catch(Exception ex)
{
System.Console.WriteLine("Error: " + ex.Message);
}
}

public void ListPersons()
{
System.Console.WriteLine("\nEnlisted person:");
foreach(DataRow dr in myDt.Rows)
System.Console.WriteLine(dr["Name"].ToString());
}

private void myDt_RowChanging(object sender, DataRowChangeEventArgs e)
{
if(e.Row["Name"].ToString() == "Bill")
throw new Exception("Bill can not be added here");
}

private void myDt_RowChanged(object sender, DataRowChangeEventArgs e)
{
if(e.Row["Name"].ToString() == "Ben")
System.Console.WriteLine("Warring! Ben was added!");
}
}
}

Regards,
Grzegorz
 
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