Here's an example written in VB.NET, including the dissolve geoprocessor and the associated functions I use to get the results. The InputName object can be a string of the feature class's path, or an IFeatureClass. For the DissolveField and the StateFields syntax, I would recommend running the Dissolve tool manually and inspecting the syntax of the input message.
Dim GP As New ESRI.ArcGIS.Geoprocessor.Geoprocessor
Friend Function DissolveDataset(ByVal InputName As Object, ByVal DissolveField As String, ByVal StatsFields As String, ByVal OutputName As String) As ESRI.ArcGIS.Geodatabase.IFeatureClass
Dim DissolveDS As New ESRI.ArcGIS.DataManagementTools.Dissolve
Dim Result As ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2
Try
DissolveDS.in_features = InputName
DissolveDS.dissolve_field = DissolveField
DissolveDS.statistics_fields = StatsFields
DissolveDS.out_feature_class = OutputName
Result = RunTool(DissolveDS, Nothing)
If Result Is Nothing Then
System.Windows.Forms.MessageBox.Show("Could not dissolve dataset")
Return Nothing
End If
Return ReturnFeatureClassfromResult(Result)
Catch ex As Exception
System.Windows.Forms.MessageBox.Show(ex.ToString, "Dissolve error")
Return Nothing
End Try
End Function
Friend Function ReturnFeatureClassfromResult(ByVal result As ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2) As ESRI.ArcGIS.Geodatabase.IFeatureClass
Dim GPVal As ESRI.ArcGIS.Geodatabase.IGPValue
Dim InMemFC As String
Dim GPUtil As ESRI.ArcGIS.Geoprocessing.IGPUtilities3 = New ESRI.ArcGIS.Geoprocessing.GPUtilities
Dim pOutputFC As ESRI.ArcGIS.Geodatabase.IFeatureClass
Try
GPVal = result.GetOutput(0)
InMemFC = GPVal.GetAsText()
pOutputFC = GPUtil.OpenFeatureClassFromString(InMemFC)
Return pOutputFC
Catch ex As Exception
System.Windows.Forms.MessageBox.Show(ex.ToString, "Return FeatureClass error")
Return Nothing
End Try
End Function
Private Sub ReturnMessages(ByVal pResult As ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2, ByVal Title As String)
Dim ErrorMessage As String
If pResult.MessageCount > 0 Then
For Count As Integer = 0 To pResult.MessageCount - 1
ErrorMessage += pResult.GetMessage(Count)
Next
End If
System.Windows.Forms.MessageBox.Show(ErrorMessage, Title)
End Sub
Friend Function RunTool(ByVal Process As ESRI.ArcGIS.Geoprocessor.IGPProcess, ByVal TC As ESRI.ArcGIS.esriSystem.ITrackCancel2) As ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2
Dim Result As ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2
Try
Result = CType(GP.Execute(Process, Nothing), ESRI.ArcGIS.Geoprocessing.IGeoProcessorResult2)
If Result.Status <> ESRI.ArcGIS.esriSystem.esriJobStatus.esriJobSucceeded Then ReturnMessages(Result, "Geoprocessing Error")
GP.ClearMessages()
Catch ex As Exception
ReturnMessages(Result, "Fail")
System.Windows.Forms.MessageBox.Show(ex.ToString, "Run Geoprocessor")
End Try
Return Result
End Function
