RadioButton // setUserData和getUserData不能按预期工作

Question

I am working with RadioButton s and try to use the setUserData method in order to identify them later on. After educating myself on this topic, I've been thinking that I can setUserData using the RadioButton reference and getUserData using the Toggle reference later on, just as done in this Oracle article (Example 4-4).

Now, this hasn't been working out the way I wanted and led to a lot of frustration. I discovered, that I cannot get the same userData I have set using the RadioButton reference when applying getUserData on the Toggle reference that is returned after using group.getSelectedToggle() . Does anybody know why? Or how I can avoid this issue elegantly?

I tried to make my issue clear in my SampleController.java file, which you can find below. The for loop you'll see is the first idea I came up with, but is definitely not a proper solution...

My Main.java:

public class Main extends Application {
    @Override
    public void start(Stage primaryStage) {
        try {
        Parent root = FXMLLoader.load(getClass().getResource("/application/sample.fxml"));
        primaryStage.setTitle("Demo");
        primaryStage.setScene(new Scene(root, 400, 400));
        primaryStage.show();
        } catch (Exception e) {
            System.out.println(e.toString() +
                    "\n" + e.getCause());
        }

    }

    public static void main(String[] args) {
        launch(args);
    }
}

My sample.fxml:

<VBox id="VBox" prefHeight="200" prefWidth="320" 
            xmlns:fx="http://javafx.com/fxml/1"
            fx:controller="application.SampleController">

    <Label text="Select a time, then press the button" />

    <fx:define>
        <ToggleGroup fx:id="group" />
    </fx:define>

    <RadioButton id="rBtn1" text="Button 1" toggleGroup="$group" />
    <RadioButton id="rBtn2" text="Button 2" toggleGroup="$group" />
    <RadioButton id="rBtn3" text="Button 3" toggleGroup="$group" />

</VBox>

My SampleController.java:

public class SampleController implements Initializable {

    @FXML
    ToggleGroup group = new ToggleGroup();

    RadioButton rBtn1 = new RadioButton();
    RadioButton rBtn2 = new RadioButton();
    RadioButton rBtn3 = new RadioButton();

    @Override
    public void initialize (URL url, ResourceBundle rb) {

        rBtn1.setUserData("Button 1");
        rBtn2.setUserData("Button 2");
        rBtn3.setUserData("Button 3");

        System.out.println(rBtn1.getUserData()); // prints 'Button 1'

        System.out.println(group.getToggles().get(0).getUserData()); // prints 'null'

        List<Toggle> toggles = group.getToggles();
        int i = 1;
        for (Toggle t : toggles) {
            t.setUserData("Button " + i);
            i++;
        }

        System.out.println(group.getToggles().get(0).getUserData()); // prints 'Button 1'

    }

}

Answer 1

You forgot to use "fx:id" instead of "id" for the rBtn1... Which means that rBtn1 is not the same as the rBtn1 in your fxml file.

Changing:

<RadioButton id="rBtn1" text="Button 1" toggleGroup="$group" />
<RadioButton id="rBtn2" text="Button 2" toggleGroup="$group" />
<RadioButton id="rBtn3" text="Button 3" toggleGroup="$group" />

to:

<RadioButton fx:id="rBtn1" text="Button 1" toggleGroup="$group" />
<RadioButton fx:id="rBtn2" text="Button 2" toggleGroup="$group" />
<RadioButton fx:id="rBtn3" text="Button 3" toggleGroup="$group" />

Will fix your problem.

When doing this:

System.out.println(group.getToggles().get(0).getUserData()); // prints 'null'

You are referencing the rBtn1 from the fxml file, which you can reach by Node traversal from your group, which has a correct fx:id.

When you are doing:

t.setUserData("Button " + i);

and redoing:

System.out.println(group.getToggles().get(0).getUserData()); // prints 'null'

The value has been set through the group traversal and therefore returns the expected value.

rBtn1.setUserData("Button 1");

is just setting the local class variable rBtn1's UserData.