JavaFX RadioButtons

 

Radio Buttons

§  Radio buttons are typically used to manage a group of mutually exclusive buttons – only one button in a group can be selected at any one time.

§  They are supported by the RadioButton class, which extends both ButtonBase and ToggleButton.

§  RadioButton also implements the Toggle interface.

 

§  Radio buttons are the primary control employed when the user must select only one option among several alternatives.

§  RadioButton defines two constructors.

o   default constructor.

o   Parameterized constructor

     RadioButton(String str)

              str is the label for the button.

 

§  To activate mutually exclusive nature – radio buttons must be configured into a group.

§  Only one of the buttons in the group can be selected at any time.

§  A button group is created by the ToggleGroup class, which is packaged in javafx.scene.control.

§  ToggleGroup provides only a default constructor.

§  Radio buttons are added to the toggle group by calling setToggleGroup( ) method on the button.

     final void setToggleGroup(ToggleGroup tg)

 

§  After all radio buttons have been added to the same group, their mutually exclusive behavior will be enabled.

 

§  When a RadioButton is part of a ToggleGroup, an action event is generated when the button is clicked only if the button was previously cleared. Thus, an action event is generated only when a new button is selected. If an already selected radio button is clicked, no event is generated.

 

§  To set a RadioButton as selected in initial state use setSelected( ) on the button.

          final void setSelected(boolean state)

§  If state is true, the button is selected. Otherwise, it is deselected.

 

 

 

ChangeListener: Watch for Changes in a Toggle Group

§  Action events on each button or

§  listen to the entire toggle group for changes.

o   one piece of code can watch for a change to a group of radio buttons

§  When a change takes place, the event handler can easily determine which radio button has been selected and take action accordingly.

 

§  To use this approach,

1.    register a ChangeListener on the toggle group.

2.    When a change occurs to the toggle group, the listener is executed.

3.    Inside the listener – determine which button was selected.

4.    Call selectedToggleProperty( ) on the toggle group and

5.    Register the change listener for the toggle group by calling the addListener( ) on the returned object returned.

6.    ChangeListener defines only one method, called changed( ).

void changed(ObservableValue<? extends T> changed,

T oldVal, T newVal)

 

// Demo

// Radio buttons

// Event handling and ChangeListener

 

import javafx.application.*;

import javafx.scene.*;

import javafx.stage.*;

import javafx.event.*;

import javafx.scene.layout.*;

import javafx.scene.control.*;

import javafx.scene.input.*;

import javafx.geometry.*;

import java.lang.*;

import javafx.beans.value.*;

 

public class JfxChk extends Application

{

   public static void main(String []args)

   {

        launch(args);    

   }

   public void init(){}

   public void stop(){}

  

   public void start(Stage myStage)

   {

        myStage.setTitle("Radio buttons");

       

        FlowPane fp = new FlowPane(Orientation.VERTICAL, 25, 35);

        fp.setAlignment(Pos.CENTER);

       

        Label L1 = new Label("Select Gender");

        Label L2 = new Label("Event Handler.");

        Label L3 = new Label("Change Listener.");

       

        RadioButton rb1 = new RadioButton("Male");

        RadioButton rb2 = new RadioButton("Female");

  

        ToggleGroup tg = new ToggleGroup();

        rb1.setToggleGroup(tg);

        rb2.setToggleGroup(tg);

       

        fp.getChildren().addAll(L1, rb1, rb2, L2, L3);

       

        Scene myScene = new Scene(fp, 400, 300);

       

        rb1.setOnAction(new EventHandler<ActionEvent>(){

             public void handle(ActionEvent ae)

             {

                 L2.setText("Event - Radio button Male is clicked.");

             }

        });

       

        rb2.setOnAction(new EventHandler<ActionEvent>(){

             public void handle(ActionEvent ae)

             {

                 L2.setText("Event - Radio button Female is clicked.");

             }

        });

       

       

tg.selectedToggleProperty().addListener(new ChangeListener<Toggle>()

        {

             public void changed(ObservableValue<? extends Toggle> changed,

Toggle oldval, Toggle newval)

             {

                 RadioButton rb = (RadioButton) newval;

                

                 L3.setText("Value of radio button "+rb.getText()+" is changed.");

             }

        });

  

        myStage.setScene(myScene);

        myStage.show();

   }

}

 

Sample output:

>javac --module-path "c:\Program Files\Java\javafx-sdk-21.0.1\lib" --add-modules javafx.controls JfxChk.java

 

>java --module-path "c:\Program Files\Java\javafx-sdk-21.0.1\lib" --add-modules javafx.controls JfxChk