feature store get NullReferenceException error

Question

I am trying to update a field value according to the selected OBJECTID. But get System.NullReferenceException error. Don't know what's wrong with the code.

My code is as follows:

 pActiveView = pMxDoc.FocusMap
 pMxDoc = My.ArcMap.Application.Document
 pMap = pMxDoc.FocusMap
 Dim layerNum = GetIndexNumberFromLayerName(pActiveView, "dev_db.DBO.Segment")
 Dim pFLayer As IFeatureLayer
 pFLayer = pMap.Layer(layerNum)
 Dim featureClass As ESRI.ArcGIS.Geodatabase.IFeatureClass = pFLayer.FeatureClass
 Dim feature As IFeature = pFLayer.GetFeature(1)
 Dim nameFieldIndex As Integer = pFLayer.FindField("Seg_ID")
 feature.Value(nameFieldIndex) = "12/11"
 feature.Store()

The method is called in an editing session, and confirm has the OBJECTID 1 in the specified layer.

I am using arcobjects 10.2.2 and vb.net arcmap add-in.

Answer 1

GetFeature() is a method of IFeatureClass, not IFeatureLayer.

Change this:

Dim feature as IFeature = pFLayer.GetFeature(1)

to this:

Dim feature as IFeature = pFLayer.FeatureClass.GetFeature(1)

Looks like you're creating a featureclass object but not using it.

• ppLily: Hi Icoursey, a strange thing when I am in editing session and try to update value in attribute table, when I perform feature.store and open the attribute table, all values disappear. When I exit editing session, the records return, but the value not updated. This drive me crazy, any advice on it? Thanks a lot!

Answer 2

I always recommend to check for null values when you are geting features from feature classes, feature class from feature layers, etc. That will prevent you this type of errors, and in the future will be easier to find bugs.

Dim pFLayer As IFeatureLayer
pFLayer = pMap.Layer(layerNum)
Dim featureClass As ESRI.ArcGIS.Geodatabase.IFeatureClass = pFLayer.FeatureClass
If featureClass = DbNull.value then
 Return
End If
Dim feature As IFeature = featureClass.GetFeature(1)
If feature = DbNull.value then
 Return
End If
Dim nameFieldIndex As Integer = pFLayer.FindField("Seg_ID")
If nameFieldIndex = -1 then
 Return
End If
feature.Value(nameFieldIndex) = "12/11"
feature.Store()

With that code you had recognized that the feature was null, and realized that the method "GetFeature()" from the feature layer was wrong.