Datagridview - Change yyyymmdd to mm/dd/yyyy

I have a class that among others exposes a string property "Date". The
date in this property is stored in the form yyyymmdd. Now I do the
following

1) Generate a DataGridViewTextBoxColumn column for that property
2) Add the column to the datagridview
3) Populate a BindingSource by adding all instances of the above
mentioned class.
4) Assign the BindingSource to the datagridview's DataSource property

At this point the column with the date shows the date in the form
yyyymmdd. I now try to change that by reading the cell's value, convert
it to mm/dd/yyyy and set the new cell value. Unfortunately, this has no
effect at all. Even in debug mode when I change the value manually in
the watch window it refuses the new value without any exception.

I guess the first question is if it is possible at all to change the
value of a cell without(!) propegating that change back to the data
source. If it is possible how is it done? If it is not possible then
how can I achive my goal?

Thanks

rob wrote:

I have a class that among others exposes a string property "Date". The
date in this property is stored in the form yyyymmdd. Now I do the
following

1) Generate a DataGridViewTextBoxColumn column for that property
2) Add the column to the datagridview
3) Populate a BindingSource by adding all instances of the above
mentioned class.
4) Assign the BindingSource to the datagridview's DataSource property

At this point the column with the date shows the date in the form
yyyymmdd. I now try to change that by reading the cell's value, convert
it to mm/dd/yyyy and set the new cell value. Unfortunately, this has no
effect at all. Even in debug mode when I change the value manually in
the watch window it refuses the new value without any exception.

I guess the first question is if it is possible at all to change the
value of a cell without(!) propegating that change back to the data
source. If it is possible how is it done? If it is not possible then
how can I achive my goal?

Thanks

Have you tried to set the DataFormatString to {0:MM/dd/yyyy} ? (Not that
this specific date format makes any sense to me - I'd take the original
ISO Date format over that any day...)

I have a class that among others exposes a string property "Date". The
date in this property is stored in the form yyyymmdd. Now I do the
following

1) Generate a DataGridViewTextBoxColumn column for that property
2) Add the column to the datagridview
3) Populate a BindingSource by adding all instances of the above
mentioned class.
4) Assign the BindingSource to the datagridview's DataSource property

At this point the column with the date shows the date in the form
yyyymmdd. I now try to change that by reading the cell's value, convert
it to mm/dd/yyyy and set the new cell value. Unfortunately, this has no
effect at all. Even in debug mode when I change the value manually in
the watch window it refuses the new value without any exception.
You can use the DataGridView's CellParsing and CellFormating events:

using System.Globalization;

private void dataGridView_CellFormatting(object sender,
DataGridViewCellFormattingEventArgs e)
{
if (dataGridView.Columns[e.ColumnIndex].DataPropertyName == "Date" )
{
DateTime dt = DateTime.ParseExact((string)e.Value, "yyyymmdd",
DateTimeFormatInfo.InvariantInfo);

e.Value = dt.ToString("mm/dd/yyyy",
DateTimeFormatInfo.InvariantInfo); //*

e.FormattingApplied = true;
}
}

private void dataGridView_CellParsing(object sender,
DataGridViewCellParsingEventArgs e)
{
if (dataGridView.Columns[e.ColumnIndex].DataPropertyName == "Date")
{
DateTime dt = DateTime.ParseExact((string)e.Value, "mm/dd/yyyy",
DateTimeFormatInfo.InvariantInfo); //*

e.Value = dt.ToString("yyyymmdd",
DateTimeFormatInfo.InvariantInfo);

e.ParsingApplied = true;
}
}

(*) you could also use "d" and DateTimeFormatInfo.CurrentInfo to show the
date in the short-date-format for the users current culture.

HTH,
Greetings

I guess the first question is if it is possible at all to change the
value of a cell without(!) propegating that change back to the data
source. If it is possible how is it done? If it is not possible then
how can I achive my goal?

Thanks

DataFormatString sounds like a property of the DataGrid from ASP.NET, not
WinForm's DataGridView.

Great, it works now. There are two problems left, though:

1) The glyph is not shown anymore on any of the colums when I set the
datasource property of my datagridview to the bindingsource. This works
fine when I create rows on my datagridview and manually set each cell's
content.
If you mean the sorting glyph, then that's because the list the
BindingSource is using doesn't support sorting. In case you didn't assign a
list to the BindingSource.DataSource then the default list is a
BindingList<T> which doesn't support sorting.

You could use a SortableBindingList<T> posted at the end of this message.
Create a Data Source (Menu-Data) for your class (eg. Customer), then from
the Data Sources window drag it on the Form. Then from code in form_load
assign the actual list to be used, example:

private void Form_Load(...)
{
someBindingSource.DataSource = new SortableBindingList<Customer>();
someBindingSource.Add( new Customer("fkdsf") );
someBindingSource.Add( new Customer("fdsf") );
}

But sorting the 'Date' column correctly while being a string would be hard
and require more code, so if it is possible use a DateTime for your Date
column.

2) This approach is much slower (factor 1.5) then by setting the
content of each cell manually. Is there a way to improve this?
Not sure about this, probely some databinding overhead, gonna have a look
later, but i doubt i'll find something.

HTH,
Greetings

The code for SortableBindingList<T> is at
http://msdn.microsoft.com/library/de...ms02182005.asp ,
but because some parts are missing, i pasted the complete code here:

using System;
using System.Reflection;
using System.Collections.Generic;
using System.Text;
using System.ComponentModel;

namespace test1.CellFormat
{
public class SortableBindingList<T> : BindingList<T>
{
private PropertyDescriptor sortProp = null;
private ListSortDirection sortDir =
ListSortDirection.Ascending;

private bool isSorted = false;

protected override bool SupportsSortingCore
{
get { return true; }
}

protected override void ApplySortCore(PropertyDescriptor property,
ListSortDirection direction)
{
PropertyComparer<T> pc =
new PropertyComparer<T>(property, direction);

((List<T>)this.Items).Sort(pc);

isSorted = true;
sortProp = property;
sortDir = direction;

// Let bound controls know they should refresh their views
this.OnListChanged(new
ListChangedEventArgs(ListChangedType.Reset, -1));
}

protected override bool IsSortedCore
{
get { return isSorted; }
}

protected override void RemoveSortCore()
{
// can't unsort
}

protected override PropertyDescriptor SortPropertyCore
{
get { return sortProp; }
}

protected override ListSortDirection SortDirectionCore
{
get { return sortDir; }
}
}

public class PropertyComparer<T> : System.Collections.Generic.IComparer<T>
{
// The following code contains code implemented by Rockford Lhotka:
//
http://msdn.microsoft.com/library/de...et01272004.asp

private PropertyDescriptor _property;
private ListSortDirection _direction;

public PropertyComparer(PropertyDescriptor property, ListSortDirection
direction)
{
_property = property;
_direction = direction;
}

#region IComparer<T>

public int Compare(T xWord, T yWord)
{
// Get property values
object xValue = GetPropertyValue(xWord, _property.Name);
object yValue = GetPropertyValue(yWord, _property.Name);

// Determine sort order
if (_direction == ListSortDirection.Ascending)
{
return CompareAscending(xValue, yValue);
}
else
{
return CompareDescending(xValue, yValue);
}
}

public bool Equals(T xWord, T yWord)
{
return xWord.Equals(yWord);
}

public int GetHashCode(T obj)
{
return obj.GetHashCode();
}

#endregion

// Compare two property values of any type
private int CompareAscending(object xValue, object yValue)
{
int result;

// If values implement IComparer
if (xValue is IComparable)
{
result = ((IComparable)xValue).CompareTo(yValue);
}
// If values don't implement IComparer but are equivalent
else if (xValue.Equals(yValue))
{
result = 0;
}
// Values don't implement IComparer and are not equivalent, so compare
as string values
else result = xValue.ToString().CompareTo(yValue.ToString());

// Return result
return result;
}

private int CompareDescending(object xValue, object yValue)
{
// Return result adjusted for ascending or descending sort order ie
// multiplied by 1 for ascending or -1 for descending
return CompareAscending(xValue, yValue) * -1;
}

private object GetPropertyValue(T value, string property)
{
// Get property
PropertyInfo propertyInfo = value.GetType().GetProperty(property);

// Return value
return propertyInfo.GetValue(value, null);
}
}
}

Thanks,

Rob,

It is easy to do, however you have to be wise.

Make from the String property a DateTime value.

With that is everything done by Microsoft what you ask.
Not if he wants to use databinding, when you have custom objects then
sorting is not supported by default (even if the property is DateTime)
because the default list used for binding is BindingList<T> which does not
support sorting. That's why he needs SortableBindingList<T>.

Greetings


(And for that is not a small amount of code that they made).

Cor