访问实体的几何数据时，抛出 SEHException错误（只有Release版出现）

上周处理了一个有趣的问题，与垃圾回收机制有关。当获取Revit中对象的几何信息，在一个函数来获得构件的Solid。然后在Caller中对solid包含的面进行遍历访问。加载运行编译的debug版时，没有问题，当用Release版时，出现SEHExpection异常。



--AccessViolationException - Attempted to read or write protected memory. This is often an indication that other memory is corrupt.



这个问题的本质是有关垃圾回收机制的。因为大家常常用到几何数据访问，这里给大家分享下产生的原因和修改方法。



源代码大概样子是这样的：

注：在你运行的时候不一定出现这个错误，与机器的资源，内存，计算过程等有关。



[TransactionAttribute(Autodesk.Revit.Attributes.TransactionMode.Manual)]
[RegenerationAttribute(Autodesk.Revit.Attributes.RegenerationOption.Manual)]
public class Lab1PlaceGroup : IExternalCommand
{
public Result Execute(
ExternalCommandData commandData,
ref string message,
ElementSet elements)
{
//Get application and document objects
UIApplication uiApp = commandData.Application;
Document doc = uiApp.ActiveUIDocument.Document;

Transaction trans = new Transaction(doc, "ExComm");
trans.Start();

//Define a Reference object to accept the pick result.
Reference pickedRef = null;

//Pick an object
Selection sel = uiApp.ActiveUIDocument.Selection;
pickedRef = sel.PickObject(ObjectType.Element,
"Please select a family instance");
Element elem = pickedRef.Element;

Options geoOptions = uiApp.Application.Create.NewGeometryOptions();
SolidArray solids = new SolidArray();
GeometryElement geoElement = elem.get_Geometry(geoOptions);

//get the transformed solid elements
GetSolids(geoElement, ref solids);

SolidArrayIterator solidIter = solids.ForwardIterator();
solidIter.Reset();
FaceArray faces = null;
while (solidIter.MoveNext())
{
faces = null;
Autodesk.Revit.DB.Solid sol = solidIter.Current as Autodesk.Revit.DB.Solid;
faces = sol.Faces;
if (faces.Size > 0) //抛出 SEHException错误，没有规律的出现。
{
TaskDialog.Show("Get faces", "the solid has " + faces.Size.ToString() + "faces");
}
}


trans.Commit();

return Result.Succeeded;
}

public void GetSolids(GeometryElement geomElem, ref SolidArray solids)
{
foreach (Autodesk.Revit.DB.GeometryObject geomObj in geomElem.Objects)
{

Autodesk.Revit.DB.Solid solid = geomObj as Autodesk.Revit.DB.Solid;
if (null != solid)
{
if (solid.Faces.Size > 0)
{
{
solids.Append(solid);
continue;
}
}
}

Autodesk.Revit.DB.GeometryInstance geomInst = geomObj as Autodesk.Revit.DB.GeometryInstance;
if (null != geomInst)
{
Autodesk.Revit.DB.GeometryElement transformedGeomElem = geomInst.GetInstanceGeometry((geomInst.Transform);
GetSolids(transformedGeomElem, ref solids);
}
}
}
}



错误原因是solid对象从GetInstanceGeometry 函数返回的transformedGeomElem 中获得。当退出拷贝solid的GetSolids（）函数回到主调用函数后，操作系统把GetInstanceGeometry 返回的transformedGeomElem 的内存回收了。这一垃圾回收，导致返回到主条用函数的solidArray失去了数据源数据。在debug版，所有的变量占用的内存收保护没有被释放掉，所以debug版运行正常。在Release版垃圾回收机制起作用，把有用的内存数据释放了。所以我们再访问时，这块内存被保护起来了。所以错误信息包含 Attempted to read or write protected memory。



解决办法有两个：



1. 把读取solid数据的代码放在遍历solid的代码后面，处于同一个函数中。这样可能transformedGeomElem 还不能释放。

2. 增加一个对象引用，指向返回的transformedGeomElem 对象，这样也不会释放，因为有人正引用它。



下面是修改后的代码。



[TransactionAttribute(Autodesk.Revit.Attributes.TransactionMode.Manual)]
[RegenerationAttribute(Autodesk.Revit.Attributes.RegenerationOption.Manual)]
public class Lab1PlaceGroup : IExternalCommand
{
public Result Execute(
ExternalCommandData commandData,
ref string message,
ElementSet elements)
{
//Get application and document objects
UIApplication uiApp = commandData.Application;
Document doc = uiApp.ActiveUIDocument.Document;

Transaction trans = new Transaction(doc, "ExComm");
trans.Start();

//Define a Reference object to accept the pick result.
Reference pickedRef = null;

//Pick an object
Selection sel = uiApp.ActiveUIDocument.Selection;
pickedRef = sel.PickObject(ObjectType.Element,
"Please select a family instance");
Element elem = pickedRef.Element;

Options geoOptions = uiApp.Application.Create.NewGeometryOptions();
SolidArray solids = new SolidArray();
GeometryElement geoElement = elem.get_Geometry(geoOptions);

GeometryElement refGeometry = null; //对象保护，防止几何数据被释放掉了,后面产生SEHException.
//get the transformed solid elements
GetSolids(geoElement, ref solids,ref refGeometry);

SolidArrayIterator solidIter = solids.ForwardIterator();
solidIter.Reset();
FaceArray faces = null;
while (solidIter.MoveNext())
{
faces = null;
Autodesk.Revit.DB.Solid sol = solidIter.Current as Autodesk.Revit.DB.Solid;
faces = sol.Faces;
if (faces.Size > 0) //这里再也不会出现问题了。
{
TaskDialog.Show("Get faces", "the solid has " + faces.Size.ToString() + "faces");
}
}

trans.Commit();

return Result.Succeeded;
}

public void GetSolids(GeometryElement geomElem, ref SolidArray solids, ref GeometryElement refGeometry)
{
foreach (Autodesk.Revit.DB.GeometryObject geomObj in geomElem.Objects)
{

Autodesk.Revit.DB.Solid solid = geomObj as Autodesk.Revit.DB.Solid;
if (null != solid)
{
if (solid.Faces.Size > 0)
{
{
solids.Append(solid);
continue;
}
}
}

Autodesk.Revit.DB.GeometryInstance geomInst = geomObj as Autodesk.Revit.DB.GeometryInstance;
if (null != geomInst)
{

refGeometry = geomInst.GetInstanceGeometry(geomInst.Transform);
GetSolids(refGeometry, ref solids,ref refGeometry);
}
}
}
}



这里增加了refGeometry 来指向GetInstanceGeometry所返回的对象到主调用函数。保护了目标对象不释放。