vb.net - Subclassing DatagridView, onPaint event -

i subclassing datagridview extend , bind common functionailty.
here overrides few (about 10) events , work ok except onpaint event.

code:

imports system.componentmodel  public class xdatagridview inherits datagridview  private _selected_row integer protected overrides sub onpaint(byval e system.windows.forms.painteventargs)      sel_row = me.currentrow.index + 1     mybase.onpaint(e) end sub  <browsable(true)> _ public property sel_row() integer             return _selected_row     end     set(byval value integer)         _selected_row = value     end set end property end class 

in main form contains class under _paint event handler selected row common property: mysel_row = mydgv.sel_row
when try open designer main form in vbide on place of dgv big red 'x' red border.

system.nullreferenceexception: object reference not set instance of object.

but if start program works normally. other events class work , doesn't report that.

what may cause of error?

i think problem current row datagridview in design view null. that's what's causing system.nullreferenceexception, , if read message box comes , tells error, says error on line: sel_row = me.currentrow.index + 1. 1 way fix problem this:

protected overrides sub onpaint(byval e system.windows.forms.painteventargs)      if (not isnothing(me.currentrow)) sel_row = me.currentrow.index + 1     mybase.onpaint(e) end sub 

i pasted code posted , got error did, , adding conditional statement check if current row null keeps exception being thrown when you're in design view. (you'll have build project rid of error message that's in control.) hth