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Hi,
Shortly.
It's a better practice to use a using statement which insure the object will be disposed even if an exception occurs.
Always dispose instances of Transaction and DocumentLock.
Any object opened with the transaction using Transaction.GetObject or ObjectId.GetObject() or added to the Transaction using Transaction.AddNewlyCreatedObject() will be automatically disposed when the Transaction is disposed.
Any newly created object (with new) have to be explicitly disposed if it is not (or possibly may not be) added to the Transaction.
Anyway, while you're not certain a disposable object need to be disposed or will be automatically disposed, do dispose it explicitly.
Example with unusefull statement which works:
using (Transaction tr = db.TransactionManager.StartTransaction())
{
// this is unusefull because the object is opened with the transaction, but works
using (BlockTableRecord btr = (BlockTableRecord)tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite))
{
// this is unusefull because the circle will be added to the Transaction, but works
using (Circle circle = new Circle(Point3d.Origin, Vector3d.ZAxis, 10.0))
{
btr.AppendEntity(circle);
tr.AddNewlyCreatedDBObject(circle, true);
}
}
tr.Commit();
}
The previous example would have been safely written:
using (Transaction tr = db.TransactionManager.StartTransaction())
{
BlockTableRecord btr = (BlockTableRecord)tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite);
Circle circle = new Circle(Point3d.Origin, Vector3d.ZAxis, 10.0);
btr.AppendEntity(circle);
tr.AddNewlyCreatedDBObject(circle, true);
tr.Commit();
}
Example of unsafe code: it's needed to create a new circle instance to use with CircleJig but the circle will only be added to the transaction if Editor.Drag().Status is equal to PromptStatus.OK. If no (the use cancelled), the new Circle won't be disposed.
using (Transaction tr = db.TransactionManager.StartTransaction())
{
BlockTableRecord btr = (BlockTableRecord)tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite);
Circle circle = new Circle(Point3d.Origin, Vector3d.ZAxis, 10.0);
CircleJig jig = new CircleJig(circle);
if (ed.Drag(jig).Status == PromptStatus.OK)
{
btr.AppendEntity(circle);
tr.AddNewlyCreatedDBObject(circle, true);
}
tr.Commit();
}
Here's a safe way to write the upper code (note you can have many using statements)
using (Transaction tr = db.TransactionManager.StartTransaction())
using (Circle circle = new Circle(Point3d.Origin, Vector3d.ZAxis, 10.0))
{
BlockTableRecord btr = (BlockTableRecord)tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite);
CircleJig jig = new CircleJig(circle);
if (ed.Drag(jig).Status == PromptStatus.OK)
{
btr.AppendEntity(circle);
tr.AddNewlyCreatedDBObject(circle, true);
}
tr.Commit();
}
In the "unsafe" example, a new circle is created to be passed as argument to the CircleJig constructor.
Then the user is prompted to specify the circle center.
The user may specify a point or cancel the command during the prompt (or an exception may occur).
In the first case (the user specified a point), the newly created circle is added to transanction and so will be automatically disposed whith the transaction disposing.
In the second case (the user cancellled), the newly created circle is not added to the transaction, so it won't be diposed whith the transaction disposing, and AutocAD may crash sometimes after.
This is why I called this example "unsafe".
So if you're absolutely certain a newly created object will be added to a transaction, you can avoid to explicitly dispose it.
In all others cases, you have to dispose it explicitly (if this wasn't necessary, this is not an issue, disposing the transaction won't dispose again already disposed objects).
Tony Tanzillo, a well known and very talented AutoCAD programmer recommends as better practice to always dipose newly created database resident objects. IOW, always use:
using (Circle circle = new Circle()) { ... } or using (Line line = new Line()) { ... } and so on...
You can put the using expression at the same level of the transaction one or nest it in the transaction statement.
using (Transaction tr = db.TransactionManager.StartTransaction())
using (Circle circle = new Circle(Point3d.Origin, Vector3d.ZAxis, 10.0))
{
} // <- the circle and the transaction will be disposed here
works the same as:
using (Transaction tr = db.TransactionManager.StartTransaction())
{
using (Circle circle = new Circle(Point3d.Origin, Vector3d.ZAxis, 10.0))
{
} // <- the circle will be disposed here
} // <- the transaction will be disposed here
