Fields will not load in my combobox

Question

I have a combo box that has the layers from the TOC loaded into them.  Now I want to be able to select the layer (usually shapefiles) and load the fields but im a newbie when it comes to ArcObjects.

This is what I have which i know is wrong:

private void cboLocation_SelectedIndexChanged(object sender, EventArgs e)

{

cboRegion.Items.Clear();

cboLevel.Items.Clear();

PointLayers selectedPntLayer = cboLocation.SelectedItem as PointLayers;

IFeatureLayer selectedFL = selectedPntLayer.pointLayer as IFeatureLayer;

IFeatureClass getInputFC = selectedFL.FeatureClass ;

for (int i = 0; i < getInputFC.Fields.FieldCount; i++)

{

cboRegion.Items.Add(getInputFC.Fields.get_Field(i).Name);
                cboLevel.Items.Add(getInputFC.Fields.get_Field(i).Name);

}

I get an error at the IFeatureLayer line saying:

"Object reference not set to an instance of an object."

Im sure it is easy to fix but im a newbie, anyone out there know how to fix this?

FreddieGibson · Answer

Here is an example addin I just wrote up for this scenario. After I've had a chance to clean up the code I'll upload it to my GitHub account and send you the url. I designed my code so that it would add/remove the names of the feature layers to the first combo-box as you add, remove, or reorder layers in the TOC. When you select a name from the first combo-box it populates the names of the fields into the second combo-box. Code for first combo-box using System; using System.Collections.Generic; using System.Text; using System.IO; using System.Linq; namespace ArcMapAddinCBX { public class LayerCombo : ESRI.ArcGIS.Desktop.AddIns.ComboBox { public LayerCombo() { var events = ArcMap.Document.FocusMap as ESRI.ArcGIS.Carto.IActiveViewEvents_Event; events.ItemAdded += (item) => { System.Diagnostics.Debug.WriteLine("Item Added"); if (!(item is ESRI.ArcGIS.Carto.IFeatureLayer)) return; this.Add((item as ESRI.ArcGIS.Carto.ILayer).Name); }; events.ItemDeleted += (item) => { System.Diagnostics.Debug.WriteLine("Item Deleted"); if (!(item is ESRI.ArcGIS.Carto.IFeatureLayer)) return; var items = new Dictionary<string, Stack<int>>(); foreach (var i in this.items) { var key = i.Caption; if (items.ContainsKey(key)) items[key].Push(i.Cookie); else { var stack = new Stack<int>(); stack.Push(i.Cookie); items[key] = stack; } } var name = (item as ESRI.ArcGIS.Carto.ILayer).Name; if (!items.ContainsKey(name)) return; var cookies = items[name]; foreach (var cookie in cookies) this.Remove(cookie); }; events.ItemReordered += (item, toIndex) => { System.Diagnostics.Debug.WriteLine("Item Reordered"); this.Clear(); // "{40A9E885-5533-11D0-98BE-00805F7CED21}" = IFeatureLayer var names = LoopThroughLayersOfSpecificUID(ArcMap.Document.FocusMap, "{40A9E885-5533-11D0-98BE-00805F7CED21}"); foreach (var name in names) this.Add(name); }; } protected override void OnUpdate() { Enabled = ArcMap.Application != null; } protected override void OnSelChange(int cookie) { if (cookie < 0) return; var name = this.items.Where(s => s.Cookie == cookie).FirstOrDefault().Caption; var layer = LoopThroughLayersOfSpecificUID(ArcMap.Document.FocusMap, "{40A9E885-5533-11D0-98BE-00805F7CED21}", name) as ESRI.ArcGIS.Carto.IFeatureLayer; var fields = new List<string>(); for (int i = 0; i < layer.FeatureClass.Fields.FieldCount; i++) fields.Add(layer.FeatureClass.Fields.Field[i].Name); var cbx = ESRI.ArcGIS.Desktop.AddIns.AddIn.FromID<FieldsCombo>(ThisAddIn.IDs.FieldsCombo.ToUID().Value.ToString()); cbx.UpdateItems(fields.ToArray()); base.OnSelChange(cookie); } // Loop Through Layers of Specific UID Snippet (ArcObjects .NET 10.4 SDK) // http://desktop.arcgis.com/en/arcobjects/latest/net/webframe.htm#68527c4d-e69d-42f2-9f9e-81652dd4c329.htm public string[] LoopThroughLayersOfSpecificUID(ESRI.ArcGIS.Carto.IMap map, System.String layerCLSID) { if (map == null || layerCLSID == null) return null; List<string> names = new List<string>(); ESRI.ArcGIS.esriSystem.IUID uid = new ESRI.ArcGIS.esriSystem.UIDClass { Value = layerCLSID }; try { ESRI.ArcGIS.Carto.IEnumLayer enumLayer = map.get_Layers(((ESRI.ArcGIS.esriSystem.UID)(uid)), true); // Explicit Cast enumLayer.Reset(); ESRI.ArcGIS.Carto.ILayer layer; while ((layer = enumLayer.Next()) != null) names.Add(layer.Name); } catch (System.Exception ex) { System.Diagnostics.Debug.WriteLine(ex.Message); } return names.ToArray(); } public ESRI.ArcGIS.Carto.ILayer LoopThroughLayersOfSpecificUID(ESRI.ArcGIS.Carto.IMap map, System.String layerCLSID, System.String layerName) { if (map == null || layerCLSID == null || layerName == null) return null; ESRI.ArcGIS.esriSystem.IUID uid = new ESRI.ArcGIS.esriSystem.UIDClass { Value = layerCLSID }; try { ESRI.ArcGIS.Carto.IEnumLayer enumLayer = map.get_Layers(((ESRI.ArcGIS.esriSystem.UID)(uid)), true); // Explicit Cast enumLayer.Reset(); ESRI.ArcGIS.Carto.ILayer layer; while ((layer = enumLayer.Next()) != null) { if (layer.Name == layerName) return layer; } } catch (System.Exception ex) { System.Diagnostics.Debug.WriteLine(ex.Message); } return null; } // Find Command and Execute Snippet (ArcObjects .NET 10.4 SDK) // http://desktop.arcgis.com/en/arcobjects/latest/net/webframe.htm#c3a1599b-b5ce-4822-9b65-2dc7c9f527e8.htm public ESRI.ArcGIS.Desktop.AddIns.ComboBox FindCommand(ESRI.ArcGIS.Framework.IApplication application, ESRI.ArcGIS.esriSystem.UID commandUid) { ESRI.ArcGIS.Framework.ICommandBars commandBars = application.Document.CommandBars; ESRI.ArcGIS.Framework.ICommandItem commandItem = commandBars.Find(commandUid, false, false); if (commandItem != null) return commandItem as ESRI.ArcGIS.Desktop.AddIns.ComboBox; return null; } } } ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ Code for second combo-box using System; using System.Collections.Generic; using System.Text; using System.IO; using System.Linq; namespace ArcMapAddinCBX { public class FieldsCombo : ESRI.ArcGIS.Desktop.AddIns.ComboBox { public static FieldsCombo hook; public FieldsCombo() { hook = this; } public void UpdateItems(string[] items) { this.Clear(); foreach (var item in items) this.Add(item); } protected override void OnSelChange(int cookie) { if (cookie < 0) return; var name = this.items.Where(s => s.Cookie == cookie).FirstOrDefault().Caption; System.Windows.Forms.MessageBox.Show("You Selected " + name + " from the ComboBox!!"); base.OnSelChange(cookie); } } } ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ Code for the toolbar <Name>ArcMapAddinCBXName> <AddInID>{d306126e-c332-457b-804e-d944fc88a07b}AddInID> <Description>Description> <Version>1.0Version> <Image>Images\ArcMapAddinCBX.pngImage> <Author>FreddieAuthor> <Company>Company> <Date>9/8/2016Date> <Targets> <Target name="Desktop" version="10.4" /> Targets> <AddIn language="CLR" library="ArcMapAddinCBX.dll" namespace="ArcMapAddinCBX"> <ArcMap> <Commands> <ComboBox id="ArcMapAddinCBX_LayerCombo" class="LayerCombo" message="List of Feature Layers in the Map" caption="Layer Combo Box" tip="Select a Feature Layer" category="Add-In Controls" image="Images\LayerCombo.png" sizeString="WWWWWWWWWWWWWWW" itemSizeString="WWWWWWWWWWWWWWW" /> <ComboBox id="ArcMapAddinCBX_FieldsCombo" class="FieldsCombo" message="List of Fields in the Layer." caption="Fields Combo Box" tip="Select a Field Name" category="Add-In Controls" image="Images\FieldsCombo.png" sizeString="WWWWWWWWWWWWWWW" itemSizeString="WWWWWWWWWWWWWWW" /> Commands> <Toolbars> <Toolbar id="ArcMapAddinCBX_CBX_Toolbar" caption="CBX Toolbar" showInitially="true"> <Items> <ComboBox refID="ArcMapAddinCBX_LayerCombo" /> <ComboBox refID="ArcMapAddinCBX_FieldsCombo" separator="true" /> Items> Toolbar> Toolbars> ArcMap> AddIn> ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ Video Showing How it Works ....coming soon

kenbuja · Answer

Here's one example of an add-in where I fill a combobox with the fields of a layer selected from another combobox. When I initialize the form in the function CreateLayerList, I fill the layer combobox with specific layer types (point, line, or polygon) while excluding other layer types (rasters, group layers, etc). The SelectedIndexChanged function then fills the combobox with fields from the selected layer. Private pEnumLayers As ESRI.ArcGIS.Carto.IEnumLayer Private pSampleLayer As ESRI.ArcGIS.Carto.ILayer2 Private Sub CreateLayerList() Dim pFLayer As ESRI.ArcGIS.Carto.IFeatureLayer2 Dim pLayer As ESRI.ArcGIS.Carto.ILayer cboLayer.Items.Clear() Try If My.ArcMap.Document.FocusMap.LayerCount > 0 Then pEnumLayers = My.ArcMap.Document.FocusMap.Layers pLayer = pEnumLayers.Next Do Until pLayer Is Nothing If pLayer.Valid Then If TypeOf pLayer Is ESRI.ArcGIS.Carto.IFeatureLayer2 Then pFLayer = pLayer If pFLayer.ShapeType = ESRI.ArcGIS.Geometry.esriGeometryType.esriGeometryPolygon Or pFLayer.ShapeType = ESRI.ArcGIS.Geometry.esriGeometryType.esriGeometryPoint Or pFLayer.ShapeType = ESRI.ArcGIS.Geometry.esriGeometryType.esriGeometryPolyline Then cboFrame.Items.Add(pLayer.Name) End If End If pLayer = pEnumLayers.Next Loop End If Catch ex As Exception System.Windows.Forms.MessageBox.Show("Error initializing list") End Try End Sub Private Sub cboLayer_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cboLayer.SelectedIndexChanged Dim pFields As ESRI.ArcGIS.Geodatabase.IFields Dim pFLayer As ESRI.ArcGIS.Carto.IFeatureLayer2 cboMetricField.Items.Clear() cboMetricField.Text = "" If pEnumLayers Is Nothing Then Exit Sub pEnumLayers.Reset() pSampleLayer = pEnumLayers.Next Do Until pSampleLayer Is Nothing If pSampleLayer.Name = cboLayer.Text And Not TypeOf pSampleLayer Is ESRI.ArcGIS.Carto.IGroupLayer Then Exit Do pSampleLayer = pEnumLayers.Next Loop If pSampleLayer Is Nothing Then System.Windows.Forms.MessageBox.Show("Cannot find the layer '" & cboLayer.Text & "'...exiting routine.", "", Windows.Forms.MessageBoxButtons.OK, Windows.Forms.MessageBoxIcon.Exclamation) Exit Sub End If pFLayer = pSampleLayer pFields = pFLayer.FeatureClass.Fields For i As Integer = 0 To pFields.FieldCount - 1 If pFields.Field(i).Type < 4 Then cboMetricField.Items.Add(pFields.Field(i).Name) Next End Sub‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

jameljoseph · Answer

Hello thanks for the response.   I could not find what I was looking for on those sites.