C# Discussion Boards - CodeProject

9-Jul-05 7:30

The answer is a little more complicated than it should be....Or at least I thought it should be.

The following code is meant to take the value of the cell (that the user has selected and changed)and write this value into the database. It then refreshes the DataGrid to show the new value.

The hardest part to understand is that you have to create a DataGridTableStyle object to do this. The reason for creating this object is that the class provides the necessary methods and properties that you need to access.

<br />
private void updateButton_Click(object sender, System.EventArgs e)<br />
{<br />
//DataGridTableStyle provides the mechanisms<br />
DataGridTableStyle ts1 = new DataGridTableStyle();<br />
<br />
//DataGridCell allows you to hold the contents of the specified cell<br />
DataGridCell myCell;<br />
myCell = UserdataGrid.CurrentCell;<br />
<br />
// map the DataGridTableStyle object to the database source <br />
ts1.MappingName = "SessionTable";<br />
<br />
//Add the DataGridTableStyle object to the grid's TableStyles collection<br />
UserdataGrid.TableStyles.Add(ts1);<br />
<br />
string infoStr = null;<br />
int j = 0;<br />
<br />
//The two foreach statements is a loop within a loop<br />
//The outer loop deals with the row index<br />
//The inner loop returns the column number (j) if there is a match<br />
//and the infoStr(column to change)<br />
foreach(DataGridTableStyle gridStyle in UserdataGrid.TableStyles)<br />
{<br />
<br />
foreach(DataGridColumnStyle colStyle in gridStyle.GridColumnStyles)<br />
{<br />
if (j == myCell.ColumnNumber)<br />
{<br />
infoStr = colStyle.MappingName;<br />
}<br />
j++;<br />
}<br />
//end inner foreach<br />
}<br />
//end outer foreach<br />
<br />
//The element selection has been found <br />
//and the current row index is where it can be found	<br />
int i = UserdataGrid.CurrentRowIndex;<br />
<br />
//Get the unique id associated with this row<br />
//Note that I needed to make this GUID id part of <br />
//my DataTable so that when I update the sql table<br />
//I am updating only that particular record<br />
//and not other records that may have similiar entries<br />
String userId = UserdataGrid[i, 7].ToString();<br />
<br />
//The UpdateRecord method creates an SQL update statement<br />
//Parameters are:<br />
//Table to change<br />
//Column to change<br />
//Column to search for GUID id<br />
//match on GUID id will determine row index<br />
//Value to update<br />
sql.UpdateRecord("SessionTable", infoStr, "UserId", userId, UserdataGrid[myCell].ToString());<br />
<br />
//Now all we need to do is show the changes in the DataGrid<br />
FillData();<br />
UserdataGrid.SetDataBinding(dataSet, "SessionTable");<br />
UserdataGrid.Refresh();<br />
}<br />
<br />

Whoooo!!! It sure seems like alot of work just to get a value, change it and then display the changes. But there are some positive things to note:

1) This is the entire implementation(minus the sql statements for the database and the implementation of FillData())
2) I did not have to use EditCommand
3) Though not the most elegent solution, it works!

Well, I hope this helps. I know what it's like to wonder why something isn't working when it looks like it should. Sometimes we need to look outside of the "logical box" to make it work.............

Have a good one,

Snowblind37 aliasing as CodeBlind37 these days.

List definition in C#

zaboboa8-Jul-05 9:07

8-Jul-05 9:07

How come I cant define the List type using the statement:

List<int> intList = new List<int>();

it seems it does not recognize the List definition.

Thank you.

Stefan Troschuetz8-Jul-05 9:38

8-Jul-05 9:38

Did you wrote a using directive for the correct namespace, so the use of types in that namespace is allowed without having to specify the namespace.?

zaboboa8-Jul-05 9:41

8-Jul-05 9:41

The only directive that I think I need is System.Collections;
And that is what I have.
Do I need some other directives to use List

Thank you

Stefan Troschuetz8-Jul-05 10:03

8-Jul-05 10:03

The System.Collections namespace doesn't contain a List type. There are ArrayList or SortedList type and IList interface.

Snowblind379-Jul-05 8:01

Search & replacing values in Xml

9-Jul-05 8:01

There is no List definition in C#. I suggest you go to http://msdn.microsoft.com/ . There you will be able to find the definitions of all the classes available. They are mostly the same for C# and VB, etc. Actual class names will differ from Java but the functionality will be more or less the same.

CodeBlind37

breen258-Jul-05 9:05

breen25

8-Jul-05 9:05

Hi,
I've got a program that reads field names and values from a database table and searches Xml documents for them. I find them in the Xml file using XPath XPathNavigator and the XPathNodeIterator objects. However, I can't find a method that replaces a node value once I find it, I've looked through other classes such as XmlWrite, XmlNode, etc but I can't find anything suitable.

There must be something in .NET that repalces a node(tag) value in Xml according to the node structure??

MDI child can't close itself

Luis Alonso Ramos8-Jul-05 9:00

Luis Alonso Ramos

8-Jul-05 9:00

Hello,

I'm trying to close a MDI child (by calling this.Close()) is trying in the Validated event handler for one of its controls, but it refuses to close.

I've checked the OnClosing handler, and when called, e.Cancel is always true. I tried setting it to false, but then I get a NullReferenceException (not in my code, my debugger just pops up pointing at the last line of code in my Main).

I could just hide it, but I would like it to be closed later, so it's not taking up memory unnecessarily.

It seems that when I try to close it, it's in some process that has to finish, and that's the reason of the NullReferenceException.

Could anyone shed some light?

-- LuisR

Luis Alonso Ramos
Intelectix - Chihuahua, Mexico

Not much here: My CP Blog!

Re: MDI child can't close itself

Snowblind379-Jul-05 8:24

Re: MDI child can't close itself

9-Jul-05 8:24

A few things come to mind........

-What other signal flow might be trying to run? I would find this out before anything. Do you have an infinate loop going on somewhere? A reference to a method that is waiting for information?

- The NullReferenceException is likely because it hasn't reached the OnClosing handler

- Does the code even reach your this.Close(). Try printing out an "I'm here" before the Close and see if it is even getting that far

- Not a bad idea to print out statements all the way through the flow and see where it crashes

Hope that helps

CodeBlind37

Luis Alonso Ramos9-Jul-05 9:54

Luis Alonso Ramos

9-Jul-05 9:54

I've solved it. I already had a timer firing every 1/4 of a second, so I just set a flag mustClose to true, and in the timer the form closes itself. And it works fine.

But I still have the doubt on why it didn't work.

Snowblind37 wrote:
What other signal flow might be trying to run? I would find this out before anything. Do you have an infinate loop going on somewhere? A reference to a method that is waiting for information?

No. Nothing else. Basically on the Validated event, if it finds a duplicate asks on how to proceed (in a modal form) and if user chooses to work on the duplicate, Close() is called before returning from the event handler.

Snowblind37 wrote:
The NullReferenceException is likely because it hasn't reached the OnClosing handler

It's after the OnClosing. I've verified it in the debugger, and the exception only happens if I set e.Cancel to false in the OnClosing handler (which misteriously is set to true.)

Snowblind37 wrote:
Does the code even reach your this.Close().

Yes, and from there it goes to the OnClosing handler, with e.Cancel set to true (it's not a base class where a derived class could set it before.)

Snowblind37 wrote:
Not a bad idea to print out statements all the way through the flow and see where it crashes

I've stepped through all my code in the debugger. The crash is only when I try to set e.Cancel = false in the OnClosing handler, and it occurs after my handler returns, somewhere in the middle of the framework code.

When I have some time, I'll try to reproduce it in a simpler program.

Thanks for your comments!

-- LuisR

Luis Alonso Ramos
Intelectix - Chihuahua, Mexico

Not much here: My CP Blog!

Re: MDI child can't close itself

Snowblind379-Jul-05 11:20

best way to connect to a database?

9-Jul-05 11:20

Excellent!!! I'm glad to hear that you got it going.

As to why this may have been happening? Your timer was probably using most of the processor time as well as being the focus of your program running time. Setting that flag was a way of making your program do something else.

I suggest that you create a new thread for your timer and make sure it sleeps, then awakes at certain intervals.

Code On and Good Luck!!!

CodeBlind

Jassim Rahma8-Jul-05 7:32

Jassim Rahma

8-Jul-05 7:32

I would like to know what is the best way to onnect to connect to a database in general which provides you with full functionality & fast access?

Best Regards,
Jassim Rahma

Re: best way to connect to a database?

breen258-Jul-05 8:47

breen25

8-Jul-05 8:47

You have a number of options based largely on performence and security. You could consider using a DataAdaptor (OleDbDataAdapter/SqlDataAdaptor with a DataSet/DataTable from System.Data.OleDb and System.Data.SqlClient respectivly) with a command builder for retrieving and updataing data. DataAdaptors can be useful when you are working with data from multiple data sources (dbs, tables, etc).
Alternativly, the DataReader can be used if your dealing with large volumes of data (e.g so much you exceed a single cache) and want to streamline and optmise data access to your source.

A starting point anyway... Smile | :)

Simple Instance Error Msg

zaboboa8-Jul-05 5:32

8-Jul-05 5:32

I have a simple setup outlined below, but when I try to run it I get this message: Object reference not set to an instance of an object.
Why do I get this message, if I declare the dataset in the declaration
section of the class ProjectSetup

Here is the setup:

public class ProjectSetup : System.Windows.Forms.Form {
.
.
.
private DataSet dataset = new DataSet();

// Constructor
public ProjectSetup ()
{
.
.
PopulateLocationComboBox();
}

private void PopulateLocationComboBox ()
{
// Populate ComboBox
foreach (DataRow row in this.dataset.Tables["Location"].Rows)
{
string item = row["Name"].ToString();
this.comboBoxLocation.Items.Add(item);
} // End of FOREACH statement
}

private void ProjectSetup_Load(object sender, System.EventArgs e)
{
.
.
adapterLocation.Fill(dataset, "Location");
}
}

Error message occurs in PopulateLocationComboBox () in foreach statement
when I am trying to access the dataset.

Thank you.

Dave Kreskowiak8-Jul-05 5:42

Dave Kreskowiak

8-Jul-05 5:42

It throws that exception probably because you don't have a table in the dataset called Location. You might want to check for it before you try to get the Rows collection out of it.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

Stefan Troschuetz8-Jul-05 5:51

8-Jul-05 5:51

ProjectSetup_Load is called after the constructor, so there is no table Location in your dataset and the exception is thrown.

zaboboa8-Jul-05 6:14

8-Jul-05 6:14

Thank you, I already figured that out with print statements.
I really apreciate the help.

Stefan Troschuetz8-Jul-05 9:40

8-Jul-05 9:40

Help is what we are there for Smile | :)

And it's good to here that you didn't only wait for an answer, but figured out the problem yourself.