索引超出范围。必须为非负值并小于集合大小。这是怎么回事啊

Question

public static ISpatialReference GetSpatialReference(IFeatureDataset pFeatureDataset)
{
IGeoDataset pGeoDataset = pFeatureDataset as IGeoDataset;
ISpatialReference pSpatialReference = pGeoDataset.SpatialReference;
return pSpatialReference;
}
public static List GetAllFeatureClass(IWorkspace workspace)
{
IEnumDataset dataset = workspace.get_Datasets(esriDatasetType.esriDTFeatureDataset);
IFeatureDataset featureDataset = dataset as IFeatureDataset;

             List<IFeatureDataset> featureDatasetList = new List<IFeatureDataset>();
             while (featureDataset != null)
             {
                 featureDatasetList.Add(featureDataset);
                 featureDataset = dataset.Next() as IFeatureDataset;
             }
             return featureDatasetList;
         }
         public static IWorkspace GetShapefileWorkspace(string sFilePath)
         {
             try
             {
                 IWorkspaceFactory factory = new ShapefileWorkspaceFactoryClass();
                 sFilePath = System.IO.Path.GetDirectoryName(sFilePath);
                 return factory.OpenFromFile(sFilePath, 0);
             }
             catch
             {
                 return null;
             }
         }
    private void 属性ToolStripMenuItem_Click(object sender, EventArgs e)
    {

        IWorkspace workspace = GetShapefileWorkspace(@"C:\Users\10977\Desktop\AE\培训数据\空间分析\1为新学校选址\新学校选址.mxd");
        List<IFeatureDataset> lfd = GetAllFeatureClass(workspace);

        ISpatialReference isr = GetSpatialReference(lfd[0]);
        string st=isr.Name.ToString();
        Form2 fr =new Form2();
        fr.Show();
    }
            ISpatialReference isr = GetSpatialReference(lfd[0]);这句话提示索引超出范围。必须为非负值并小于集合大小。求解啊

Answer 1

List lfd = GetAllFeatureClass(workspace);
ISpatialReference isr = GetSpatialReference(lfd[0]);

你看你写的代码，你要知道lfd是个引用类型，引用类型就可能会为null，那么你是不是需要判断lfd是否为null呢，再者，lfd即使不为null，但是可能这个集合里面没有元素呢，也就是长度为0 呢？ 你说的这个错误就是长度为0 的时候，你去取下标为0的元素就会报错的。

正确写法：
using System.Linq;

List lfd = GetAllFeatureClass(workspace);
if(null != lfd && lfd.Any())
{
ISpatialReference isr = GetSpatialReference(lfd[0]);
}