When implementing policy for your application, you must decide which policy events to handle. The policy data type will often determine which events your application handles.
When policy is applied, the system broadcasts the WM_SETTINGCHANGE message to all desktops and an event is signaled. Applications that receive messages can use the message to respond to a policy change. The lParam parameter points to the string "Policy". The wParam parameter is 1 if computer policy was applied or zero if user policy was applied. If required, you can reread the policy settings by calling the GetGPOList function to retrieve the list of GPOs.
Extension snap-ins and applications that do not have a window to receive messages can use the RegisterGPNotification function to receive notification when there is a policy change.
For more information, see the following topics: