来自：http://zhihu.esrichina.com.cn/?/question/12087

Engine中执行gp工具返回的【解决办法】：
需要用gpUtils.DecodeFeatureLayer方法将gp工具生成的图层先读取出来，如：

// Intialize the geoprocessor.

Geoprocessor GP = new Geoprocessor();

// Intialize the MakeFeatureLayer tool.

MakeFeatureLayer makefeaturelayer = new MakeFeatureLayer();

// Set up the GP tool parameters and run the tool.

makefeaturelayer.in_features = @C:\gp\nfld.gdb\wells;

makefeaturelayer.out_layer = Wells_Lyr;

makefeaturelayer.where_clause = WELL_YIELD > 150;

IGeoProcessorResult result = (IGeoProcessorResult)GP.Execute(makefeaturelayer, null);

IFeatureClass fc;

IQueryFilter qf;

IGPUtilities gpUtils = new GPUtilitiesClass();

gpUtils.DecodeFeatureLayer(result.GetOutput(0), out fc, out qf);

IFeatureCursor cursor = fc.Insert(true);

要素图层如何获取？比如make query layer工具