How do I customize the GridGroupExpanderCell?

[OverCoded]

I am using VS2010 Premium and the most recent version of Telerik WinForms. I have a custom RadGrid wit hierarchical data and I want to change the default ugly expander cell from the large unformatted plus and minus. I have tried to change it with the VSB but the only attribute I seem to be able to modify is the line color and the scaling. I know this can be modified because I have seen other grids with different expander cell styles. Can anyone shed some light on this seeing that Telerik has decided to keep it a secret?

[Jack]

Hi Mark Coe,

Please follow these steps:

1. Select GroupExpanderCell from the Elements pane
2. Expand the row
3. Select and right click in the property grid
4. Select the No filter option
5. Locate the SignStyle property

There are a lot of properties that can be customized. If you want you can use images. In this case change the SignStyle to Image and set the SignImage property.

You can do this with code by handling the ViewCellFormatting event. Here is a sample:

void radGridView1_ViewCellFormatting(object sender, CellFormattingEventArgs e)
{
    GridGroupExpanderCellElement cell = e.CellElement as GridGroupExpanderCellElement;
    if (cell != null)
    {
        cell.SignStyle = GridExpanderPrimitive.SignStyles.Triangle;
    }
}

Should you have any other questions, please feel free to contact me.

Kind regards,
Jack
the Telerik team

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[Carlos]

I would like to use my own images and programmatically change the image when expanded or contracted.
I was looking at the group.expanded property of the radgrid to change the image but I don't know how to reference the element from there.
Thanks

[Stefan]

Hello Carlos,

One way to change the desired images is to edit the theme(s) that you use and set the images to the appropriate states for the ExpanderItem (see attached image). You can use Visual Style Builder to edit your themes.

Alternatively, you cause the ViewCellFormatting event to do that:

void radGridView1_ViewCellFormatting(object sender, Telerik.WinControls.UI.CellFormattingEventArgs e)
{
    GridGroupExpanderCellElement expanderCell = e.CellElement as GridGroupExpanderCellElement;
    if (expanderCell != null)
    {
        if (e.Row.IsExpanded)
        {
            expanderCell.Expander.SignImage = Resources.expanded;
        }
        else
        {
            expanderCell.Expander.SignImage = Resources.collapsed;
        }
    }
}

In addition you might need to invalidate the row when an expand action occurs. The GroupExpanded event is suitable for this:

void radGridView1_GroupExpanded(object sender, GroupExpandedEventArgs e)
{
    e.DataGroup.GroupRow.InvalidateRow();
}

I hope that you find this information useful. Should you have any other questions, do not hesitate to contact us.

Regards,
Stefan
Telerik