Using an AsyncCallback Delegate and State Object - .NET

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• request

• Dns.EndGetHostEntry

• When you use an AsyncCallback delegate to process the results of the asynchronous operation in a separate thread, you can use a state object to pass information between the callbacks and to retrieve a final result.

• AsyncCallback Delegate

• State Object

• demonstrates using asynchronous methods in the Dns class to retrieve Domain Name System (DNS) information for user-specified computers.

• uses the HostRequest class to store state information.

• A HostRequest object gets created for each computer name entered by the user.

• This object is passed to the BeginGetHostByName method.

• The ProcessDnsInformation method is called each time a request completes.

• The HostRequest object is retrieved using the AsyncState property.

• The ProcessDnsInformation method uses the HostRequest object to store the IPHostEntry returned by the request or a SocketException thrown by the request.

• HostRequest

• a state object that holds each requested host name,

• an associated IPHostEntry object or a SocketException.

• hostName

• SocketException e

• IPHostEntry entry

• AsyncCallback callBack = new AsyncCallback(ProcessDnsInformation);

• HostRequest request = new HostRequest(host);