onColumnCollapse

the event occurs after a group of columns has been collapsed

void onColumnCollapse(number ind,boolean state);

ind	number	the index of the first column of the group
state	boolean	the state of the collapse: true - the column was collapsed, false - the column was expanded

Available only in PRO Edition

mygrid.attachEvent("onColumnCollapse",function(ind,state){
    // your code here
});