外部参照在CAD绘图中也扮演着重要角色，设计人员经常将外部图纸作为参照载入当前图纸，用于比对图纸信息或成果组织。
本文针对外部参照，封装加载、卸载、删除、查询接口，卸载接口尤其值得注意。
加载外部参照
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| public static ObjectId AttachXref(this Database db, string dwgPath, string xrefName, Point3d insertPoint)
{
ObjectId refId = db.AttachXref(dwgPath, xrefName);
if (!refId.IsNull)
{
var blockRef = new BlockReference(insertPoint, refId);
db.AddEntity(blockRef);
DwgOperators.ThisEditor.UpdateScreen();
return blockRef.ObjectId;
}
return ObjectId.Null;
}
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卸载外部参照
注意：卸载外部参照时，最好一并删除，否则每次打开图形会提示外部参照未加载。
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| public static bool UnloadXrefByName(this Database db, string xrefName)
{
bool flag = false;
using (Transaction tran = db.TransactionManager.StartTransaction())
{
BlockTable bt = tran.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable;
foreach (ObjectId id in bt)
{
BlockTableRecord btr = tran.GetObject(id, OpenMode.ForRead) as BlockTableRecord;
if (btr.IsFromExternalReference && btr.Name == xrefName)
{
db.UnloadXrefs(new ObjectIdCollection(new ObjectId[] { id }));
db.DetachXref(id);
flag = true;
break;
}
}
tran.Commit();
}
DwgOperators.ThisEditor.UpdateScreen();
return flag;
}
public static bool SearchXrefByName(this Database db, string xrefName)
{
bool flag=false;
using (Transaction tran = db.TransactionManager.StartTransaction())
{
BlockTable bt = tran.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable;
foreach (ObjectId id in bt)
{
BlockTableRecord btr = tran.GetObject(id, OpenMode.ForRead) as BlockTableRecord;
if (btr.IsFromExternalReference && btr.Name == xrefName)
{
flag = true;
break;
}
}
tran.Commit();
}
return flag;
}
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查询外部参照
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| public static void DeleteXrefs(this Database db)
{
if (db == null) return;
using (Transaction tran = db.TransactionManager.StartTransaction())
{
BlockTable bt = tran.GetObject(db.BlockTableId, OpenMode.ForWrite) as BlockTable;
List<ObjectId> ids = new List<ObjectId>();
foreach (ObjectId id in bt)
{
BlockTableRecord btr = tran.GetObject(id, OpenMode.ForRead) as BlockTableRecord;
if (btr.IsFromExternalReference)
ids.Add(id);
}
foreach (ObjectId id in ids)
{
BlockTableRecord btr = tran.GetObject(id, OpenMode.ForWrite, true) as BlockTableRecord;
if (btr != null)
btr.Erase();
}
tran.Commit();
}
}
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