Undo/Redo

QtNodes provides built-in undo/redo support using Qt’s undo framework.

How It Works

The BasicGraphicsScene maintains a QUndoStack. User actions automatically push commands to this stack:

Creating nodes
Deleting nodes
Creating connections
Deleting connections
Moving nodes
Duplicating nodes

Accessing the Undo Stack

BasicGraphicsScene scene(model);

// Get the undo stack
QUndoStack& undoStack = scene.undoStack();

// Wire up to UI
QAction* undoAction = undoStack.createUndoAction(this, "Undo");
undoAction->setShortcut(QKeySequence::Undo);

QAction* redoAction = undoStack.createRedoAction(this, "Redo");
redoAction->setShortcut(QKeySequence::Redo);

editMenu->addAction(undoAction);
editMenu->addAction(redoAction);

Built-in Commands

QtNodes provides these QUndoCommand implementations in UndoCommands.cpp:

Command	Description
`DeleteCommand`	Removes nodes and their connections
`DuplicateCommand`	Duplicates selected nodes
`DisconnectCommand`	Removes a connection
`ConnectCommand`	Creates a connection
`MoveNodeCommand`	Moves a node to a new position

Serialization Requirement

Undo/redo for node deletion requires serialization support. Make sure your model implements saveNode() and loadNode():

QJsonObject MyModel::saveNode(NodeId nodeId) const override
{
    // Save all data needed to recreate this node
    QJsonObject json;
    json["id"] = static_cast<qint64>(nodeId);

    QPointF pos = nodeData(nodeId, NodeRole::Position).toPointF();
    json["position"] = QJsonObject{{"x", pos.x()}, {"y", pos.y()}};

    // Save your custom data too
    json["internal-data"] = getNodeInternalData(nodeId);

    return json;
}

void MyModel::loadNode(QJsonObject const& json) override
{
    // Recreate node from saved data
    NodeId nodeId = static_cast<NodeId>(json["id"].toInt());
    _nextId = std::max(_nextId, nodeId + 1);

    _nodes.insert(nodeId);
    emit nodeCreated(nodeId);

    // Restore position
    auto pos = json["position"].toObject();
    setNodeData(nodeId, NodeRole::Position,
                QPointF(pos["x"].toDouble(), pos["y"].toDouble()));

    // Restore custom data
    restoreNodeInternalData(nodeId, json["internal-data"].toObject());
}

Warning

Without proper saveNode()/loadNode(), deleted nodes cannot be restored by undo.

Custom Undo Commands

Create custom commands for your own operations:

class ChangeNodeColorCommand : public QUndoCommand
{
public:
    ChangeNodeColorCommand(MyModel* model, NodeId nodeId, QColor newColor)
        : _model(model)
        , _nodeId(nodeId)
        , _newColor(newColor)
        , _oldColor(model->getNodeColor(nodeId))
    {
        setText(QString("Change color of node %1").arg(nodeId));
    }

    void undo() override {
        _model->setNodeColor(_nodeId, _oldColor);
    }

    void redo() override {
        _model->setNodeColor(_nodeId, _newColor);
    }

private:
    MyModel* _model;
    NodeId _nodeId;
    QColor _newColor;
    QColor _oldColor;
};

// Push to stack
scene.undoStack().push(
    new ChangeNodeColorCommand(&model, nodeId, Qt::red)
);

Grouping Commands

Use macros to group multiple commands:

undoStack.beginMacro("Batch Operation");

// These will undo/redo together
undoStack.push(new Command1(...));
undoStack.push(new Command2(...));
undoStack.push(new Command3(...));

undoStack.endMacro();

Clearing History

// Clear all undo history
undoStack.clear();

// Mark current state as "clean" (for save indicators)
undoStack.setClean();

// Check if modified since last save
if (!undoStack.isClean()) {
    // Show "unsaved changes" warning
}

Keyboard Shortcuts

Default shortcuts (handled by GraphicsView):

Ctrl+Z – Undo
Ctrl+Shift+Z or Ctrl+Y – Redo
Delete – Delete selection (creates DeleteCommand)
Ctrl+D – Duplicate (creates DuplicateCommand)