Add modal confirmation dialogue when exiting with unsaved changes

[gavanderhoorn]

As per subject: there is no confirmation requested if the user exits the application while there are still unsaved changes.

To avoid losing work - by misclicking fi - the user should be presented with a Save changes to FILENAME before closing? or similar dialogue.

[AndyZe]

The tentative plan is to check for changes to the urdf as follows:

1. Set a flag if qtpropertybrowser.cpp::propertyChanged() is called. That will indicate if a link/joint was created or changed. But it doesn't indicate if a link/joint was deleted
2. Just prior to exiting, check if the number of links/joints has changed since opening the file. That will indicate if a link/joint has been deleted.

I would have liked liked to use qtpropertybrowser::removeProperty(*) to set a flag, but it's getting called way more often than I expected.

Let me know if that sounds OK, @gavanderhoorn

[gavanderhoorn]

@AndyZelenak: the observer/observable approach was what I had in mind, so this sounds ok. Is propertyChanged() not called for remove actions?

We should probably also watch for changes in the treeviewer, to not miss changes when #26 is implemented.

[AndyZe]

@gavanderhoorn OK, I need to check if the tree is reordered. Roger that. Unfortunately propertyChanged() is not called on deletion.

How would you like this flag to be shared between the qt_property_browser and urdf_editor sides? I was thinking I would pass it as an argument to qt_property_browser, e.g. propertyChanged(bool & unsavedChanges).

I guess the other option would be a "global" namespace or class variable.

[gavanderhoorn]

Would it perhaps make sense to not monitor the properties directly, but keep track of the state of the ros_workbench parameter? All other user actions result in changes to that, so tracking it's dirty state should suffice to see whether we need to warn about loosing work at exit.

On the other hand: doing this on the Qt side would avoid introducing an additional dependency on ROS (parameter server).

[gavanderhoorn]

Btw. The QWidget documentation contains an example that shows how to implement exactly what this issue asks for. See QWidget::closeEvent(..).

[gavanderhoorn]

Closed via #74.