Using Platform.runLater to disable collapsing an Accordion in JavaFX

Question

I want to use the solution suggested in the answer at: Prevent an accordion in JavaFX from collapsing in order to prevent the Accordion in JavaFX from entirely collapsing.

My question is: why does the listener added on the expandedPaneProperty use Platform.runLater to call setCollapsible(false)?

Indeed, if I remove Platform.runLater, after collapsing/expanding the panes, their content disappears for some reason. So why does the runLater solve that problem?

Answer 1

The documentation of ChangeListener< T> states, that:

In general is is considered bad practice to modify the observed value in this method.

Where this method refers to:

void changed(ObservableValue<? extends T> observable, T oldValue, T newValue);

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RunLater ensures, that the Pane will be modiffied on the next run of the JavaFX Application Thread and so making modifications when it is safe to do them.