求指出异常。被狠批了

求指出错误。被狠批了。
为什么字段选择的时候，会有多个重复的选项？我的数据没问题的。我保证。

public partial class AttributeQueryForm : Form

    {

        //地图数据

        private AxMapControl mMapControl;

        //选中图层

        private IFeatureLayer mFeatureLayer;


        public AttributeQueryForm(AxMapControl mapControl)

        {

            InitializeComponent();

            this.mMapControl = mapControl;

        }


        private void AttributeQueryForm_Load(object sender, EventArgs e)

        {

            //MapControl中没有图层时返回

            if (this.mMapControl.LayerCount <= 0)

                return;


            //获取MapControl中的全部图层名称，并加入ComboBox

            //图层

            ILayer pLayer;

            //图层名称

            string strLayerName;

            for (int i = 0; i < this.mMapControl.LayerCount; i++)

            {

                pLayer = this.mMapControl.get_Layer(i);

                strLayerName = pLayer.Name;

                //图层名称加入cboLayer

                this.cboLayer.Items.Add(strLayerName);

            }

            //默认显示第一个选项

            this.cboLayer.SelectedIndex = 0;

        }


        private void cboLayer_SelectedIndexChanged(object sender, EventArgs e)

        {

            //获取cboLayer中选中的图层

            mFeatureLayer = mMapControl.get_Layer(cboLayer.SelectedIndex) as IFeatureLayer;

            IFeatureClass pFeatureClass = mFeatureLayer.FeatureClass;

            //字段名称

            string strFldName;

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

            {

                strFldName = pFeatureClass.Fields.get_Field(i).Name;

                //图层名称加入cboField

                this.cboField.Items.Add(strFldName);

            }

            //默认显示第一个选项

            this.cboField.SelectedIndex = 0;

        }


        private void btnOk_Click(object sender, EventArgs e)

        {

            //定义图层，要素游标，查询过滤器，要素

            IFeatureLayer pFeatureLayer;

            IFeatureCursor pFeatureCursor;

            IQueryFilter pQueryFilter;

            IFeature pFeature;

            //获取图层

            pFeatureLayer = this.mMapControl.Map.get_Layer(cboLayer.SelectedIndex) as IFeatureLayer;

            IFeatureClass pFeatureClass = pFeatureLayer.FeatureClass;