I don't know how you can add a scroll bar, but I know that you can change the list width with the well-named property :
listWidth : Number
The width (used as
a parameter to Ext.Element.setWidth)
of the dropdown list (defaults to the
width of the ComboBox field). See also
minListWidth
For an horizontal scroll, it would need lots of changes, because the list container width is forced, so "overflow" attributes in css are useless.
Edit : Another method
You can add this custom css, for me it seems to work well, as wrapping long lines.
.x-combo-list-item {
white-space:normal;
}
Of course, if you add this it will apply to all combos' lists.
You can set listClass : 'x-combo-list-wrap'
on your Ext.form.ComboBox, and then apply the css only to these items :
x-combo-list-wrap .x-combo-list-item {
white-space:normal !important;
}
(I'm not sure the !important is useful here, not tested)