AO中一般有两种方式存储图面注记元素，一种使用TextElement，它是文档级的元素，编辑后要通过文档（mxd）保存；另一种是使用Annotation要素类，它是一个独立的要素类（featureclass），需要存储到地理数据库中。使用Annotation featureclass 的方式更灵活、更强大，至于如何灵活，如何强大，待你用到便自知。
1、创建一个标准的Annotation要素类（StandardAnnotationClass）
public AnnotationMark(IFeatureClass outPolygonFc,string mdbPath,int referenceScale)
{
string annotationName = "Annotation";
IWorkspaceFactory workspaceFactory = new AccessWorkspaceFactoryClass();
IFeatureWorkspace featureWorkspace = workspaceFactory.OpenFromFile(mdbPath, ) as IFeatureWorkspace;
IGeoDataset geoDataset = outPolygonFc as IGeoDataset;
ISpatialReference spatialReference = geoDataset.SpatialReference;
Utils.UserWorkspace.FeatureWorkspace.TryDeleteFeatureClass(annotationName, featureWorkspace);
featureClass = Utils.UserWorkspace.FeatureWorkspace.CreateStandardAnnotationClass(featureWorkspace, null,annotationName, spatialReference, referenceScale, esriUnits.esriMeters, null);
}
下面是一个摘自Esri官网的代码段，可以使用它创建StandardAnnotationClass。
值得注意的是：
featureDataset根据数据库是否有数据集（dataset）而定，可以是null;
referenceScale是注记的参考比例，注记元素会以此为基准，放大或缩小，一般建议设置为出图比例尺，这样所设置的字号即出图字号。
configKeyword=""
public static IFeatureClass CreateStandardAnnotationClass(IFeatureWorkspace featureWorkspace, IFeatureDataset featureDataset, String className,
ISpatialReference spatialReference, int referenceScale, esriUnits referenceScaleUnits, String configKeyword)
{
// Create an annotation class and provide it with a name.
ILabelEngineLayerProperties labelEngineLayerProperties = new
LabelEngineLayerPropertiesClass();
IAnnotateLayerProperties annotateLayerProperties = (IAnnotateLayerProperties)
labelEngineLayerProperties;
annotateLayerProperties.Class = "Annotation"; // Get the symbol from the annotation class. Make any changes to its properties
// here.
ITextSymbol annotationTextSymbol = labelEngineLayerProperties.Symbol;
ISymbol annotationSymbol = (ISymbol)annotationTextSymbol; // Create a symbol collection and add the default symbol from the
// annotation class to the collection. Assign the resulting symbol ID
// to the annotation class.
ISymbolCollection symbolCollection = new SymbolCollectionClass();
ISymbolCollection2 symbolCollection2 = (ISymbolCollection2)symbolCollection;
ISymbolIdentifier2 symbolIdentifier2 = null;
symbolCollection2.AddSymbol(annotationSymbol, "Annotation", out
symbolIdentifier2);
labelEngineLayerProperties.SymbolID = symbolIdentifier2.ID; // Add the annotation class to a collection.
IAnnotateLayerPropertiesCollection annotateLayerPropsCollection = new
AnnotateLayerPropertiesCollectionClass();
annotateLayerPropsCollection.Add(annotateLayerProperties); // Create a graphics layer scale object.
IGraphicsLayerScale graphicsLayerScale = new GraphicsLayerScaleClass();
graphicsLayerScale.ReferenceScale = referenceScale;
graphicsLayerScale.Units = referenceScaleUnits; // Create the overposter properties for the standard label engine.
IOverposterProperties overposterProperties = new BasicOverposterPropertiesClass(); // Instantiate a class description object.
IObjectClassDescription ocDescription = new
AnnotationFeatureClassDescriptionClass();
IFeatureClassDescription fcDescription = (IFeatureClassDescription)ocDescription; // Get the shape field from the class description's required fields.
IFields requiredFields = ocDescription.RequiredFields;
int shapeFieldIndex = requiredFields.FindField(fcDescription.ShapeFieldName);
IField shapeField = requiredFields.get_Field(shapeFieldIndex);
IGeometryDef geometryDef = shapeField.GeometryDef;
IGeometryDefEdit geometryDefEdit = (IGeometryDefEdit)geometryDef;
geometryDefEdit.SpatialReference_2 = spatialReference; // Create the annotation layer factory.
IAnnotationLayerFactory annotationLayerFactory = new FDOGraphicsLayerFactoryClass(); // Create the annotation feature class and an annotation layer for it.
IAnnotationLayer annotationLayer = annotationLayerFactory.CreateAnnotationLayer
(featureWorkspace, featureDataset, className, geometryDef, null,
annotateLayerPropsCollection, graphicsLayerScale, symbolCollection, false,
false, false, true, overposterProperties, configKeyword); // Get the feature class from the feature layer.
IFeatureLayer featureLayer = (IFeatureLayer)annotationLayer;
IFeatureClass featureClass = featureLayer.FeatureClass; return featureClass;
}
2、创建Annotation要素（Annotation feature）
上面开始在AnnotationMark类的构造函数中创建了Annotation要素类featureClass，下面是创建Annotation 要素 feature的代码。
博主竟没有在墙内网络上找到相关的实现方案，只得爬墙去攒了这片代码，它主要是使用了ISymbolCollectionElement接口设置了Feature的各种属性。此外，网络上还有使用IFormattedTextSymbol接口的方案，博主并未测试，有需要可以戳下面链接：
Why do these annotations appear stacked/overlapping?（再羡国外论坛生态）
值得注意的是：
IGeometry pointGeometry 这个几何对象应该是一个IPoint;
esriTextHorizontalAlignment 与 esriTextVerticalAlignment指示这个point在Annotation元素（一个面Polygon）的哪个位置，借此确定放置位置。
ISymbolCollectionElement或者IFormattedTextSymbol还有更多的属性可以设置（本文不做补充），这些属性便是该要素记录各字段的值。
public void CreateAnnotationFeature(IGeometry pointGeometry,string text,string fontName,double fontSize,esriTextHorizontalAlignment horizontalAlignment,
esriTextVerticalAlignment verticalAlignment)
{
IFeature feature = featureClass.CreateFeature(); ISymbolCollectionElement symbolCollectionElement = new TextElementClass();
symbolCollectionElement.FontName = fontName;
symbolCollectionElement.Size = fontSize;
symbolCollectionElement.Text = text;
symbolCollectionElement.HorizontalAlignment = horizontalAlignment;
symbolCollectionElement.VerticalAlignment = verticalAlignment;
symbolCollectionElement.Geometry = pointGeometry; IElement element = symbolCollectionElement as IElement;
IAnnotationFeature2 annotationFeature2 = feature as IAnnotationFeature2;
annotationFeature2.Annotation =element;
annotationFeature2.Status = esriAnnotationStatus.esriAnnoStatusPlaced;
feature.Store();
}
3、要素类添加为图层
不啰嗦，上代码：
IWorkspaceFactory workspaceFactory = new AccessWorkspaceFactoryClass();
IFeatureWorkspace featureWorkspace = workspaceFactory.OpenFromFile(mdbPath, ) as IFeatureWorkspace;
IAnnotationLayerFactory annotationLayerFactory = new FDOGraphicsLayerFactoryClass();
IAnnotationLayer annotationLayer = annotationLayerFactory.OpenAnnotationLayer(featureWorkspace, null, "Annotation");
ILayer layer_Annotation = annotationLayer as ILayer;
layer_Annotation.Name = tfh + "_Annotation";