Problems with updating Listbox

Hey there i got a asp.net solution where i got 1 dropdownlist (filled with packages from sql) and 1 listbox (filled with software from sql) and 1 last witch should show software linked to a selected package from the dropdownlist.

the last listbox is filled with a datasource from sql when the page load.

my problem is. when i select a package in the dropdownlist i want the last listbox to update. and again when i select a software from the softwarelistbox and hit the add button, i want the last listbox to up开发者_运维技巧date when new data...

how do i do that ?

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I will assume that you're not an expert in ASP.NET, and for that I will give you an easy answer:

Give ASP.NET AJAX Control Toolkit a go, and check the Cascading DropDown as I'm sure that's what you want.