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C# DatagridView change the text entered in a cell during validation

i have a datagridView with a cell whose data type is Datetime.
The value of the cell is formatted as HH:mm (hours, minutes).
When the user edits the cell with a value like 5, I would like to transform it into 05:00 before the datagridView complains that the value entered is not a valid datetime.
I have tried the validating event but there I cannot change the Formatted value, I can only Cancel.
I know what I am asking is possible because I have done it in another project, but I cannot access the code of that project to see how I did it.
Please help. Thanks

I have solved the problem using the CellParsing event. There I get the Value entered from the user and I can parse it into a proper datetime and finally set e.ParsingApplied = true (very important otherwise the parsing you did is ignored)

Strange DateTimePicker Formatting Behavior

I have a small form that includes a DateTimePicker control. I've customized it so that it formats its dates to dd/MM/yy. However, when the user presses "send", its value is displayed in my CheckedListBox as dd/month/yy.
For example, if the user sets the date to "19/04/11", it shows up in the CheckedListBox as "19-Apr-2011". Does anyone have any suggestions as to why this may be happening? Thanks in advance.

change the format of the Date before passing to the Checkedlistbox by making it as
checkedListBox1.Items.Add(dateTimePicker1.Value.ToString("dd/MM/yy"));

Set the CustomFormat property of your DateTimePicker control to "dd/MM/yy"..
The Format property must be set to DateTimePickerFormat.Custom for this property to affect the formatting of the displayed date and time.
However, the Value property is not formatted unless the Checked property is set to true. If the Checked property was set to false only Text property value is formatted ..
Refer to:
http://msdn.microsoft.com/en-us/library/system.windows.forms.datetimepicker.customformat.aspx
http://msdn.microsoft.com/en-us/library/system.windows.forms.datetimepicker.checked.aspx

Configuring the Date Popup on the WPF DatePicker Control

I have a date picker control that I use for a data collection application. It is using MvvM data binding. When going through a list of dates (see fig1) it will populate the date picker correctly. Whenever I hit new, the date pickers are nulled out. When I pull up the popup, it selects the month and year from the previous date that was set to. (fig 2) Is there anyway to default the pop up show the current month in the current year?
Note : I would like to keep the selected date to null on a new entry to force some validation.
Fig 1
Fig 2
The following image is to show what happens when I set the DisplayDateStart.

(original answer was horribly wrong, sorry about that)
Okay, lets try this again.
Have you tried setting the fallback to today's date?
SelectedDate="{Binding TehDate, FallbackValue={x:Static sys:DateTime.Now}}"

Take the datepicker value

i have a gridview that dynamically generate datepicker , i have taken the value of datepicker using
GMDatePicker dtp = (GMDatePicker)Gridview1.Rows[rowIndex].Cells[3].FindControl("frmdate_starttime");
and i have inserted using dtp.Date,while storing in the database it only store the date and not the time. how to retrive the time to save in database along with date

You can change the Format property to Custom and the CustomFormat property to what you require, something like dd MMM yyyy hh:mm.
You should then be able to use
DateTime dt = dateTimePicker1.Value;
to get the date and time.

Split the problem into two parts: are you getting the right value out of the control but failing to save/restore it in the database correctly, or are you failing to get the right value out of the control in the first place? Once you've worked out whether it's a UI or database problem, you can ignore the other half of it.
Have you enabled the time picker in the control?
What column type are you using in the database?
If you run your application in the debugger, what value do you see before you store it in the database?
If you run a query against the database in the relevant admin tool, does that show a time?

DateTimePicker displays today's date instead of displaying its actual Value

We have a couple of DateTimePickers on a custom UserControl, on a Form. They are visible, but not enabled (for display purposes only). When the UserControl is loading, the DateTimePickers are assigned values from a DataRow that came from a DataSet which stores a single record returned from a SQL Server stored procedure.
There is an inconsistent behavior in which the users sometimes see today's date instead of the date that was assigned to the DateTimePicker. It doesn't seem to matter whether I assign the date I want to the .Value property or the .Text property:
txtstart.Value = (DateTime) dr["Group_Start_Date"];
txtend.Text = dr["Term_Date"].ToString();
I expect that of the two statements above, the one using the Value property is more appropriate. But, in both cases, today's date is displayed to the user regardless of the values that were in the database. In the case of txtstart.Value, Visual Studio shows me that the value was assigned as expected. So why isn't it displaying that date to the user instead of today's date?

I found the answer. You MUST set the checkbox value to checked to indicate a non-null value.
this.dateSold.Checked = true;
// set to true or false, as desired
this.dateSold.ShowCheckBox = false;

I was having trouble with this too and found that you indeed need to set the .Checked value to True.
I set the Checked property in the properties window and it still didn't work so I just set it in code before assigning the value and that fixed the problem.

It seems to be a problem with having multiple DateTimePickers. I was able to get around the issue (bug?) by programatically creating the DateTimePickers with the values I wanted and adding them to the form.

I ended up going with AB Nolan's suggestion. The reasoning behind a disabled DateTimePicker was never clear to me, so back on 10/23/2009, rather than continue fussing with the control I just displayed the dates I wanted in TextBoxes instead.