Dns.BeginGetHostEntry Method (String, AsyncCallback, Object)
Asynchronously resolves a host name or IP address to an IPHostEntry instance.
Assembly: System (in System.dll)
'Declaration <HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)> _ Public Shared Function BeginGetHostEntry ( _ hostNameOrAddress As String, _ requestCallback As AsyncCallback, _ stateObject As Object _ ) As IAsyncResult
- Type: System.String
The host name or IP address to resolve.
- Type: System.AsyncCallback
An AsyncCallback delegate that references the method to invoke when the operation is complete.
- Type: System.Object
A user-defined object that contains information about the operation. This object is passed to the requestCallback delegate when the operation is complete.
The BeginGetHostEntry method queries a DNS server for the IP address that is associated with a host name or IP address.
Note This member emits trace information when you enable network tracing in your application. For more information, see Network Tracing in the .NET Framework.
This method does not block until the operation is complete. To block until the operation is complete, use the GetHostEntry method.
For detailed information about using the asynchronous programming model, see Calling Synchronous Methods Asynchronously.
The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.
' Signals when the resolve has finished. Dim Shared GetHostEntryFinished As ManualResetEvent = New ManualResetEvent(False) ' Define the state object for the callback. ' Use hostName to correlate calls with the proper result. Class ResolveState Dim hostName As String Dim resolvedIPs As IPHostEntry Public Sub New(host As String) hostName = host End Sub Public Property IPs AS IPHostEntry Get Return resolvedIPs End Get Set resolvedIPs = value End Set End Property Public Property host As [String] Get Return hostName End Get Set hostName = value End Set End Property End Class ' Record the IPs in the state object for later use. Shared Sub GetHostEntryCallback(ar As IAsyncResult) Dim ioContext As ResolveState = ar.AsyncState ioContext.IPs = Dns.EndGetHostEntry(ar) GetHostEntryFinished.Set() End Sub ' Determine the Internet Protocol (IP) addresses for ' this host asynchronously. Shared Sub DoGetHostEntryAsync(hostname As String) GetHostEntryFinished.Reset() Dim ioContext As ResolveState = New ResolveState(hostname) Dns.BeginGetHostEntry(ioContext.host,AddressOf GetHostEntryCallback, ioContext) ' Wait here until the resolve completes (the callback ' calls .Set()) GetHostEntryFinished.WaitOne() Console.WriteLine("EndGetHostEntry(" + ioContext.host + ") returns:") Dim ip As IPAddress() = ioContext.IPs.AddressList Dim index As Integer For index = 0 To ip.Length - 1 Console.WriteLine(ip(index)) Next index End Sub