How to set tooltips to combobox items # VB.NET? - vb.net

Question

I have a combobox with a given width.
It may occur that one row of the data is partially hidden (the combobox might be too narrow). I'd like to show the whole line by using a tooltip or right-click context menu.
Currently I can't find how to 'catch' the row that I'm currently holding on or passing over by mouse. Please tell me.
Thanks in advance!

Answer 1

Have you tried to increase the DropDownWidth property so that everything is visible?
Edit: To find the ideal width based on the items in the list:
var maxLength = 0;
// using the ComboBox to get a Graphics object:
using (var g = Graphics.FromHwnd(comboBox2.Handle)) {
foreach (var item in comboBox2.Items.Cast<string>()) {
var itemLength = g.MeasureString(item, comboBox2.Font);
maxLength = Math.Max((int) itemLength.Width, maxLength);
}
}
if (comboBox2.Items.Count > comboBox2.MaxDropDownItems) {
// correction when ScrollBar is displayed
maxLength += 15;
}
comboBox2.DropDownWidth = maxLength;
I put this code in the DropDown event of the ComboBox for testing. Maybe you can find a better place for it, like after populating the ComboBox...

Answer 2

Going in the same direction that Julien went, here is a generic extension method that will resize the drop down area regardless of how the combobox is filled (manually with strings or via data binding).
<Extension()> _
Public Sub AutosizeDropDownWidth(ByVal combobox As ComboBox)
Dim longestItem As Integer = 0
Using g = Graphics.FromHwnd(combobox.Handle)
Dim itemsAsText = (From item In combobox.Items _
Select combobox.GetItemText(item))
longestItem = CInt(itemsAsText.Max(Function(text) g.MeasureString(text, combobox.Font).Width))
End Using
' Account for scrollbar
If (combobox.Items.Count > combobox.MaxDropDownItems) Then longestItem += 15
' Resize as needed (but never smaller than the default width)
combobox.DropDownWidth = Math.Max(longestItem, combobox.Width)
End Sub
To use it then you can simply do the following...
Private Sub MyCombobox_DropDown(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyCombobox.DropDown
MyCombobox.AutosizeDropDownWidth()
End Sub
Note, I didn't test corner cases like an empty combobox in this code example.

Answer 3

Your're right, there really isn't a "Item.OnMouseOver", but I suppose you could (off the top of my head, so I've likely forgotten something)...
inherit from ComboBox,
override OnDrawItem (you may need to turn change .DrawMode to "Owner Drawn").
you will know which item is hovered in the OnDrawItem event/override from the EventArgs.
Set the tooltip on the control at that point.
optionally set a timer to manually show the tooltip if the above doesn't work automatically.