Test undo / redo w/ unmount

[scottdover]

Summary

This demonstrates an issue w/ undo / redo when a diagram is unmounted / remounted. You can follow the steps below to reproduce:

• Run yarn start
• Drag a node somewhere on the diagram
• See that you can undo it
• Drag the node again
• toggle the display off
• toggle the display on
• At this point, the nodes position will have been persisted. However, there is no longer an option to undo the position change

One thing I attempted to resolve the issue was to add...

public componentDidUnmount() {
    this.diagramRef.current &&
        this.diagramRef.current.clear();
}

to DiagramWrapper (after reading "A Note on Diagram Reinitialization" here: https://gojs.net/latest/intro/react.html). This unfortunately didn't resolve the issue.

[jonchardy]

This is intentional behavior of gojs-react. The diagram is forgotten when unmounted such that memory isn't held when the diagram is no longer in use.

If you want to persist the diagram when mounting/unmounting, you'll probably want to fork the gojs-react repository and change the behavior of componentDidMount and componentWillUnmount. The implementation is described here: https://github.com/NorthwoodsSoftware/gojs-react/blob/master/IMPLEMENTATION.md