DropDown Resizing - WinForms DropDownList Control

DropDownSizingMode

RadDropDownList supports different sizing modes, based on the DropDownSizingMode property of the control.

The SizingMode enumeration has the following members:

None: no sizing is allowed.

Figure 1: SizingMode.None

WinForms RadDropDownList SizingMode None

SizingMode.None

RightBottom: allows sizing in horizontal direction.

Figure 2: SizingMode.RightBottom

WinForms RadDropDownList SizingMode RightBottom

SizingMode.RightBottom

UpDown: allows sizing in vertical direction.

Figure 3: SizingMode.UpDown

WinForms RadDropDownList SizingMode UpDown

SizingMode.UpDown

UpDownAndRightBottom: allows sizing in both directions.

Figure 4: SizingMode.UpDownAndRightBottom

WinForms RadDropDownList SizingMode UpDownAndRightBottom

SizingMode.UpDownAndRightBottom

Fixed size

You can specify a fixed height or width of the drop-down by setting the DropDownHeight and DropDownWidth properties.

Figure 5: DropDownHeight

WinForms RadDropDownList DropDownHeight

DropDownHeight

Figure 6: DropDownWidth

WinForms RadDropDownList DropDownWidth

DropDownWidth

You can set the DropDownMinSize property in order to specify the exact minimum height and width for the drop-down.

Figure 7: DropDownMinSize

WinForms RadDropDownList DropDownMinSize

DropDownMinSize

Auto size

The following example demonstrates a sample approach how to handle the RadDropDownList.PopupOpening event and achieve auto size functionality for the pop up in RadDropDownList:

Auto size drop down

C#
VB.NET

private void RadDropDownList1_PopupOpening(object sender, CancelEventArgs e)
{
    RadDropDownListElement list = sender as RadDropDownListElement;
    float width = 0;
    for (int x = 0; x < list.Items.Count(); x++)
    {
        width = Math.Max(width, TextRenderer.MeasureText(list.Items[x].Text, list.Font).Width);
    }
    if (list.Items.Count * (list.ItemHeight-1) > list.DropDownHeight)
    {
        width += list.ListElement.VScrollBar.Size.Width;
    }
    list.Popup.Width = (int)width;
}

Private Sub RadDropDownList1_PopupOpening(sender As Object, e As CancelEventArgs)
    Dim list As RadDropDownListElement = TryCast(sender, RadDropDownListElement)
    Dim width As Single = 0
    For x As Integer = 0 To list.Items.Count() - 1
        width = Math.Max(width, TextRenderer.MeasureText(list.Items(x).Text, list.Font).Width)
    Next
    If list.Items.Count * (list.ItemHeight - 1) > list.DropDownHeight Then
        width += list.ListElement.VScrollBar.Size.Width
    End If
    list.Popup.Width = CInt(width)
End Sub
'#End Region
'#Region "FilteringPredicate"
Private Function FilterItem(item As RadListDataItem) As Boolean
    If item.Text.StartsWith("L") Then
        Return True
    End If

    Return False
End Function

Default pop up size	Auto sized popup

Displayed items

By default, RadDropDownList displays 6 items in the pop-up. In case you need to change this number you can set the DefaultItemsCountInDropDown property:

Figure 8: DefaultItemsCountInDropDown

WinForms RadDropDownList DefaultItemsCountInDropDown