CheckBox - JavaFX

CheckBox

The CheckBox class encapsulates the functionality of a check box. Its immediate superclass is ButtonBase. Although you are no doubt familiar with check boxes because they are widely used controls, the JavaFX check box is a bit more sophisticated than you may at first think. This is because CheckBox supports three states. The first two are checked or unchecked, as you would expect, and this is the default behavior. The third state is indeterminate (also called undefined). It is typically used to indicate that the state of the check box has not been set or that it is not relevant to a specific situation. If you need the indeterminate state, you will need to explicitly enable it.

CheckBox defines two constructors. The first is the default constructor. The second lets you specify a string that identifies the box. It is shown here:

CheckBox(String str)

It creates a check box that has the text specified by str as a label. As with other buttons, a CheckBox generates an action event when it is selected.

Here is a program that demonstrates check boxes. It displays check boxes that let the user select various deployment options, which are Web, Desktop, and Mobile. Each time a check box state changes, an action event is generated and handled by displaying the new state (selected or cleared) and by displaying a list of all selected boxes.

// Demonstrate Check Boxes.

import javafx.application.*; import javafx.scene.*;

import javafx.stage.*; import javafx.scene.layout.*; import javafx.scene.control.*; import javafx.event.*;

import javafx.geometry.*;

public class CheckboxDemo extends Application {

CheckBox cbWeb;

CheckBox cbDesktop;

CheckBox cbMobile;

Label response;

Label allTargets;

String targets = "";

public static void main(String[] args) {

// Start the JavaFX application by calling launch().

launch(args);

}

// Override the start() method.

public void start(Stage myStage) {

     //Give the stage a title.

     myStage.setTitle("Demonstrate Checkboxes");

     //Use a FlowPane for the root node. In this case,

     //vertical and horizontal gaps of 10.

FlowPane rootNode = new FlowPane(10, 10);

     //Center the controls in the scene.

     rootNode.setAlignment(Pos.CENTER);

     //Create a scene.

Scene myScene = new Scene(rootNode, 230, 140);

// Set the scene on the stage.

myStage.setScene(myScene);

Label heading = new Label("Select Deployment Options");

     //Create a label that will report the state of the

     //selected check box.

response = new Label("No Deployment Selected");

     //Create a label that will report all targets selected.

     allTargets = new Label("Target List: <none>");

     //Create the check boxes.

cbWeb = new CheckBox("Web");

cbDesktop = new CheckBox("Desktop"); cbMobile = new CheckBox("Mobile");

// Handle action events for the check boxes.

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

public void handle(ActionEvent ae) { if(cbWeb.isSelected())

response.setText("Web deployment selected."); else

response.setText("Web deployment cleared.");

showAll();

}

});

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

public void handle(ActionEvent ae) {

if(cbDesktop.isSelected()) response.setText("Desktop deployment selected.");

else

response.setText("Desktop deployment cleared.");

showAll();

}

});

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

public void handle(ActionEvent ae) {

if(cbMobile.isSelected())

response.setText("Mobile deployment selected."); else

response.setText("Mobile deployment cleared.");

showAll();

}

});

     //Use a separator to better organize the layout.

     Separator separator = new Separator(); separator.setPrefWidth(200);

     //Add controls to the scene graph.

rootNode.getChildren().addAll(heading, separator, cbWeb, cbDesktop, cbMobile, response, allTargets);

// Show the stage and its scene.

myStage.show();

}

// Update and show the targets list.

void showAll() {

targets = "";

if(cbWeb.isSelected()) targets = "Web ";

if(cbDesktop.isSelected()) targets += "Desktop "; if(cbMobile.isSelected()) targets += "Mobile";

if(targets.equals("")) targets = "<none>";

allTargets.setText("Target List: " + targets);

}

}

Sample output is shown here:

The operation of this program is straightforward. Each time a check box is changed, an action command is generated. To determine if the box is checked or unchecked, the isSelected( ) method is called.

As mentioned, by default, CheckBox implements two states: checked and unchecked. If you want to add the indeterminate state, it must be explicitly enabled. To do this, call setAllowIndeterminate( ), shown here:

final void setAllowIndeterminate(boolean enable)

In this case, if enable is true, the indeterminate state is enabled. Otherwise, it is disabled. When the indeterminate state is enabled, the user can select between checked, unchecked, and indeterminate.

You can determine if a check box is in the indeterminate state by calling isIndeterminate( ), shown here:

final boolean isIndeterminate( )

It returns true if the checkbox state is indeterminate and false otherwise.

You can see the effect of a three-state check box by modifying the preceding program. First, enable the indeterminate state on the check boxes by calling setAllowIndeterminate( ) on each check box, as shown here:

cbWeb.setAllowIndeterminate(true);

cbDesktop.setAllowIndeterminate(true);

cbMobile.setAllowIndeterminate(true);

Next, handle the indeterminate state inside the action event handlers. For example, here is the modified handler for cbWeb:

cbWeb.setOnAction(new EventHandler<ActionEvent>() { public void handle(ActionEvent ae) {

if(cbWeb.isIndeterminate())

response.setText("Web deployment indeterminate."); else if(cbWeb.isSelected())

response.setText("Web deployment selected."); else

response.setText("Web deployment cleared.");

showAll();

}

});

Now, all three states are tested. Update the other two handlers in the same way. After making these changes, the indeterminate state can be selected, as this sample output shows:

Here, the Web check box is indeterminate.