This doesn't seem to turn the background mask on for a block with multiline attribute. Anyone know what will?
BlockReference blkRef = (BlockReference)tr.GetObject(blkId, OpenMode.ForRead);
BlockTableRecord btr = (BlockTableRecord)tr.GetObject(blkRef.BlockTableRecord, OpenMode.ForRead);
AttributeCollection attCol = blkRef.AttributeCollection;
foreach (ObjectId attId in attCol)
{
AttributeReference attRef = (AttributeReference)tr.GetObject(attId, OpenMode.ForRead);
if (attRef.IsMTextAttribute)
{
btr.UpgradeOpen();
attRef.UpgradeOpen();
attRef.MTextAttribute.BackgroundFillColor = Autodesk.AutoCAD.Colors.Color.FromColorIndex(Autodesk.AutoCAD.Colors.ColorMethod.None, 198);
attRef.MTextAttribute.UseBackgroundColor = false;
attRef.UpdateMTextAttribute();
blkRef.RecordGraphicsModified(true);
}
}