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DNS Lookup with Heartbeat Event Callbacks and Abort Capability
DNS lookup Visual Basic example. This example demonstrates how to do a DNS lookup with event callbacks. The DNS lookup may be aborted while in progress. Dim WithEvents socket As ChilkatSocket Private bAbortDns As Boolean ' This called when an "Abort" button in the user interface ' is pressed. Private Sub AbortButton_Click() bAbortDns = True End Sub ' Do a DNS hostname lookup. ' Translates an IP hostname (such as "www.chilkatsoft.com") ' into an IP address string (such as "168.144.70.227") Private Sub DnsButton_Click() bAbortDns = False ProgressBar1.Value = 0 ' Create a Chilkat Socket object and unlock. Set socket = New ChilkatSocket success = socket.UnlockComponent("Anything for 30-day trial") If (success = 0) Then MsgBox "Failed to unlock component" Exit Sub End If Dim hostname As String ' You may wish to test the code with both valid and invalid hostnames. ' hostname = "www.123abc32893489.com" hostname = "www.chilkatsoft.com" ' Uncomment this line to simulate a long DNS lookup time to allow you ' to test your application's behavior while a DNS lookup is in progress. ' (units are in milliseconds) ' socket.DebugDnsDelay = 3000 ' Set our hearbeat event interval time in milliseconds: socket.HeartbeatMs = 200 ' The total DNS lookup timeout (in milliseconds) is passed as an argument totalTimeoutMs = 10000 Dim ipAddr As String ipAddr = socket.DnsLookup(hostname, totalTimeoutMs) If Len(ipAddr) = 0 Then MsgBox socket.LastErrorText Else MsgBox hostname & " = " & ipAddr End If End Sub ' The heartbeat event is called when a blocking call is in progress, ' such as a DNS lookup... ' Each Chilkat Socket object has a unique objectID ' The object ID is passed to the heartbeat event to allow ' your application to know which socket object fired the event. Private Sub socket_Heartbeat(ByVal objectID As Long, abort As Long) ' Indicate that the DNS lookup is proceeding... newValue = ProgressBar1.Value + 5 If newValue <= ProgressBar1.Max Then ProgressBar1.Value = newValue End If ' Call DoEvents to allow the application to process user-interface events. DoEvents ' Did the Abort button get pressed? If bAbortDns Then ' Setting abort = 1 causes the DNS lookup to abort. abort = 1 Else ' Setting abort = 0 causes the DNS lookup to continue waiting. abort = 0 End If End Sub
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