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c#esriarcobjectsarcmap

How to Convert ILayer to IPolygon In ArcObjects

Having trouble converting an Ilayer to an IPolygon.

I am developing a toolbar for ArcMap and I grab a layer via code from the side table of contents. The Layer is a Polygon, but the code won't convert it to a IPolygon.

Can anyone help me out? This is the code I am using to try and convert it to a IPolygon...

 IPolygon poly = m_document.Maps.get_Item(0).get_Layer(0) as IPolygon;

I can do this:

 ILayer layer = m_document.Maps.get_Item(0).get_Layer(0) as ILayer;

And that works, just not converting it to a IPloygon..

Solution

  • If you want to access the geometries contained in a shapefile layer, you have to get the layer's feature class. This is a property of the IFeatureLayer interface, so you'll have to cast your layer (which is an ILayer) first:

    IFeatureLayer FLayer = layer as IFeatureLayer;
IFeatureClass FClass = FLayer.FeatureClass;

    If you have a feature class, you can get features by index (slow) or by defining a cursor on the feature class (this is fast and the preferred way when you want to handle lots of features. Search for IFeatureCursor; ESRI docs usualy come with good code snippets).

    If your feature class contains only one feature, or if you only want one feature, You can use the GetFeature method:

    IFeature MyFeature = FClass.GetFeature(0);

    Now you're almost there. A feature's geometry is tucked away in its Shape property:

    IPolygon MyPoly = MyFeature.Shape as IPolygon;

    The extra cast is needed because the Shape property is an IPolygon, which is a more specific IGeometry.