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Oundroni
Asked: 2020-07-09 02:35:17 +0800 CST 2020-07-09 02:35:17 +0800 CST

Avoid Callback to a Listener

  • 772

I'm detecting the change of a button group's value with a Listener. If there is nothing selected I put the previous value before the change, but this causes me to call back to ListenerHow can I avoid it?

The code is:

toggleGroup.selectedToggleProperty().addListener(
    (ObservableValue<? extends Toggle> arg0, Toggle oldValue, Toggle newValue) -> {
        if (toggleGroup.getToggles().indexOf(toggleGroup.getSelectedToggle()) == -1) {                
                    toggleGroup.selectToggle(oldValue); // esto provoca rellamada al Listener
                }
            }
        );
javafx

2 Answers

  1. Best Answer

    You can create a flag that indicates if you have tried to override all the options of the toggleGroup:

    boolean flag = false; // variable gobal

toggleGroup.selectedToggleProperty().addListener(
(ObservableValue<? extends Toggle> arg0, Toggle viejo, Toggle nuevo) -> {            

    if (flag){              
        flag = false;
        return;
    }           

    if (nuevo == null){                                                   
        flag = true;               
        toggleGroup.selectToggle(viejo);
        return;
    }

});
    • 1

  2. EDIT: what I describe below after the line seems incorrect. I put another answer.

    If you save in a global variable the value you are assigning you can avoid a second call:

    String newValueAux = "";

toggleGroup.selectedToggleProperty().addListener(
(ObservableValue<? extends Toggle> arg0, Toggle oldValue, Toggle newValue) -> {
    if (toggleGroup.getToggles().indexOf(toggleGroup.getSelectedToggle()) == -1) {                
                if (oldValue != newValueAux) {
                     newValueAux = oldValue;
                     toggleGroup.selectToggle(oldValue);
                }
            }
        }
    );

    I don't know how to prevent the callback of the listener being in its own declaration, but you can end this recursion with a base condition.

    If oldValue = newValuethen you don't change anything and the listenerwill not launch:

    toggleGroup.selectedToggleProperty().addListener(
(ObservableValue<? extends Toggle> arg0, Toggle oldValue, Toggle newValue) -> {
    if (toggleGroup.getToggles().indexOf(toggleGroup.getSelectedToggle()) == -1) {                
                if (oldValue != newValue) toggleGroup.selectToggle(oldValue);
            }
        }
    );
    • 0