如果选择了列表框项，如何设置viewmodel属性？

I have a listbox...and it is bound to list of items of type (class) "A". Class "A" has a boolean property "IsCurrentViewActive". This is false by default. When user select an item in listbox....i need to set the "IsCurrentViewActive" property of corresponding item to TRUE.I have a listbox...and it is bound to list of i