window form's combo box

I am using the combobox in a window form and datasource property of that is the arraylist.
Now when the arraylist changes the combobox shows the new arraylist items in the dropdown but the selected item is that of the previous one.
i use the datasource property set to null before binding it and also tryed the refresh() and the invalidate() but these are not working.

the code are as:

Combobox1.datasource=null;
Combobox1.datasource=arraylist1;

can anyone help me.

Thnx in advance.

please show how you change the arrayList

the arraylist are the variable and the arraylist are fill by the xml file which is declare in another class on the values of the xml the arrayliast are fill.

reset the selectedindex property to -1 before changing the datasource, this way the previously selected item will not be shown