IFeatureLayer GetLayerByName(string name)
{
    ILayer layer = null;
    for(int i=0;i<axMapConTrol1.LayerCount;i++)
    {
        layer = axMapControl1.get_Layer(i);
        if(layer.Name.Equals(name))
            return layer as IFeatureLayer;
	}
    return null;
}

IFeatureLayer featureLayer = GetLayerByName("图层名") as IFeatureLayer;
IFeatureClass featrueClass = featureLayer.Feature;
//添加字段
IFieldEdit fieldEdit = new FieldClass() as IFieldEdit;
fieldEdit.Type_2 = esriFieldType.esriFieldTypeString;
fieldEdit.Name_2 = "字段名";
//还可设置字段的其他属性
featureClass.AddField(fieldEdit as IField);
//删除字段
IFields fields = featureClass.Fields;
  //查找字段
IField field = fields.get_Field(fields.FindField("字段名"));
featureClass.DeleteField(field);

IFeatureLayer featureLayer = GetLaerByName("图层名称");
IFeatureClass featureLayer = featureLayer.FeatureClass;
//查询条件
IQueryFilter queryFilter = new QueryFilterClass();
//sql语句的Where部分
queryFilter.WhereClause = "FID = 1";
//Search方法第一个参数为查询条件，为null获得所有要素
//为IQueryFilter是属性查询，为ISpatialFilter则是空间查询
//第二个参数为true表示不能更改属性
//返回指示要素的光标
IFeatureCursor cursor = featureClass.Search(queryFilter,true);
IFeature feature = cursor.NextFeature();
//通过while循环遍历所的要素
while(feature != null)
{
    //....一些操作
    feature = cursor.NextFeature();
}

IFeatureLayer featureLayer = GetLayerByname("图层名称");
IFeatureSelection featureSelection = featureLayer as IFeatureSelection;
IQueryFilter queryFilter = new QueryFilterClass();
queryFilter.WhereClause = "FID = 1";
//第一个参数同上，第二个参数表示如何将选中的元素添加进元素集，第三个参数表示是否只选一个
//选中元素将自动高亮显示
featureSelection.SelectFeatures(queryFilter,esriSelectionResultEnum.esriSelectionResultAddNew,false);
ISelectionSet selectionSet = featureSelection.SelectionSet;
//通过id遍历选中要素
IEnumIDs ids = selectionSet.IDs;
long id = ids.Next();
if(id != -1)
{
    //通过id获得要素
    IFeature feature = featureLayer.FeatureClass.GetFeature(id);
    //...一些操作
    id = ids.Next();
}

//mapcontrol的点击事件 实现用鼠标在地图画出矩形 然后查询图层中与矩形相交的要素
private void axMapControl1_OnMouseDown(object sender, IMapControlEvents2_OnMouseDownEvent e)
{
 //清除选中要素
    axMapControl1.Map.ClearSelection();
	IFeatureLayer featureLayer = GetLayerByName("图层名称");
	IFeatureClass featureClass = featureLayer.FeatureClass();
	ISpatialFilter spatialFilter = new SpatialFilterClass();
    //获取在地图上画出的矩形
	IEnvelop env = axMapControl1.TrackRectangle;
    //设置查询参数
	spatialFilter.Geometry = enc as IGeometry;//查询几何体
    //查询的空间参考类型 此处是相交
    spatialFilter.SpatialRel = esriSpatialRelEnum.esriSpatialRelIntersects;
    //第一个参数是ISpatialFilter 是空间查询
    IFeatureCursor cursor = featureCLass.Search(spatialFilter,true);
    IFeature feature = cursor.NextFeature();
	//通过while循环遍历所的要素
	while(feature != null)
	{
    	//....一些操作
    	feature = cursor.NextFeature();
	}
}

//有两种方式使查询结果高亮，各有各的特点
//其一跟上面介绍的属性查询高亮一样，将SelectFeature方法的第一个参数换为ISpatialFilter即可
//这种方法可以得到查询要素集但比方法二复杂
//其二如下  这种更简单 但得不到选中要素集  根据不同情况使用
//参数一为查询几何体，参数二为查询包络线
axMapControl1.Map.SelectByShape(geometry, null, true);//第三个参数为是否只选中一个
//选中要素高亮显示
axMapControl1.Refresh(esriViewDrawPhase.esriViewGeoSelection, null, null);