Converting Arcobjects in VB.Net to C#

Question

I am attempting to learn ArcObjects using a tutorial that uses VB.NET and I am trying to convert it to C#. I have Visual C# 2008 Express Edition. This is an ArcMap Add-In project that creates a button that displays a message box with the name of the top most layer in the data frame. Here is the VB.NET code:

Dim pMxDoc As IMxDocument
pMxDoc = My.ArcMap.Application.Document
Dim pMap As IMap
pMap = pMxDoc.FocusMap 
Dim pFLayer As IFeatureLayer2
pFLayer = pMap.Layer(0)

Dim strDisplayField As String
strDisplayField = pFLayer.DisplayField

MsgBox(strDisplayField, vbOKOnly, "Test")

My conversion in C# so far:

using ESRI.ArcGIS.ArcMapUI:
using ESRI.ArcGIS.Carto;

IMxDocument pMxDoc = ArcMap.Application.Document as IMxDocument;
IMap pMap = pMxDoc.FocusMap;
IFeatureLayer2 pFLayer = pMap.

There is no 'Layer' property. Only 'LayerCount' to choose from. I even tried this:

IFeatureLayer2 pFLayer = ArcMap.Application.Document as IFeatureLayer2;
pFLayer = pMap.

this didn't work either. I have looked all over the ArcMap Object Diagram and I can't find the FeatureLayer2 class anywhere. According to ArcObjects SDK for .NET there is a Layer member for the IMap interface, but I don't have access to that. Any help would be grealty appreciated.

Answer 1

Try this:

IFeatureLayer GetFirstFeatureLayer()
{
    IMxDocument document = ArcMap.Document;
    IMap map = document.FocusMap;
    ILayer layer = map.get_Layer(0);
    return layer as IFeatureLayer;
} 

Answer 2

It sounds like you need to spend some time reading the documentation. I would start with the topic Using ArcObjects (COM-based) in .NET.

You are not using the right interfaces and classes. You cannot query interface (QI) from IDocument to IFeatureLayer2, for example. Avoid using the as operator and use explicit casting instead. This will immediately result in an InvalidCastException if no compatible interfaces were found, aiding in debugging such issues, rather than setting the object to null and later resulting in the potentially misleading NullReferenceException in the case of as.

Also in C# 3.0, properties that take parameters (such as IMap.Layer) are accessed with a special getter method, e.g. get_Layer(i) instead of Layer[i]. It was not until C# 4.0, when support for indexed properties was added, that you can use the Layer[i] syntax to specify the index parameter. Since you are using Visual Studio 2008 you are limited to C# 3.0. Another thing to keep in mind is that ArcGIS 10.0 is limited to .NET 3.5, and while 10.1 works with .NET 4.0, it is not included in its installer.

SharpDevelop does a pretty reasonable job of converting between .NET languages. It can convert your entire solution at once, or individual files. I have not tried converting an add-in project before, so that might take some fiddling.