【转】How do I use MDGModifier so I can get reliable Undo/Redo?

 

I've had several logistical problems with MDGModifiers, exclusively with its ::undo() and ::redo() mechanism. After much trial and error on the topic I've come to the following conclusions:

There are times when you may have to perform a ::doIt() in the middle of your MDGModifier modification so the scene state is valid for further operations. For example, if you use MDGModifier::create(), you will need to ::doIt() so this node exists if you wish to perform any edits using a class other than MDGModifier (finding an MPlug on your new node, for instance).

Do not continue to use a MDGModifier object after you have called its ::doIt() method!

My "Golden Rule" for MDGModifier is now the following:

"Execute ::doIt() as soon as I need to update the state of the scene, then immediately allocate another MDGModifier for further edits. Continue, rinse, repeat."

All allocated MDGModifier nodes go onto a stack. The stack in undone in FILO order, and redone in FIFO order.

 

 

class MyCommand : public MPxNode{private: typedef std::vector<MDGModifier*>::const_iterator redoIter; typedef std::vector<MDGModifier*>::const_reverse_iterator undoIter; std::vector<MDGModifier*> mUndo;};MStatus MyCommand::doIt(){ MStatus status = MS::kSuccess; MDGModifier* modifier = NULL; // Allocate a new modifier and add to undo modifier = new MDGModifier; mUndo.push_back( modifier ); // populate modifier here... status = modifier.doIt(); modifier = NULL; // now don't touch! // Allocate another new modifier and add to undo modifier = new MDGModifier; mUndo.push_back( modifier ); // populate modifier here... status = modifier.doIt(); modifier = NULL; // now don't touch! return status;}MStatus MyCommand::redoIt(){ MStatus status = MS::kSuccess; redoIter d; for ( d = mUndo.begin(); ( status == MS::kSuccess ) && ( d != mUndo.end() ); d++ ) { status = (*d)->doIt(); } return status;}MStatus MyCommand::undoIt(){ MStatus status = MS::kSuccess; undoIter u; for ( u = mUndo.rbegin(); ( status == MS::kSuccess ) && ( u != mUndo.rend() ); u++ ) { status = (*u)->undoIt(); } return status;}