Creating Custom Controls in JavaFX

If you are looking to give a unique and sophisticated look to your JavaFX application, one way to achieve this is by designing custom controls. With JavaFX, you can create custom controls that not only have different appearances but also feature unique functionalities.

In this article, we will explore how to create your own custom controls in JavaFX. By the end of this article, you'll have an understanding of what custom controls are, how to create them, and how to style them.

Understanding Custom Controls

A custom control is a user interface element with custom functionality and visual styling. Custom controls are a powerful way to enhance the user experience by providing a unique, customized look and feel to your application. You can enrich an application with custom controls that are not available out-of-the-box with JavaFX.

With custom controls, you can tailor-make the exact functionality that your application requires. You can design custom controls with specific events and behaviors that are not possible with the standard JavaFX controls. Additionally, you can change specific attributes of an existing JavaFX control.

Custom controls in JavaFX are created with the help of the Control or SkinBase classes, which provide the essential methods and fields required for control creation.

Creating Custom Controls

To create a custom control in JavaFX, you will need to create a new Java class that extends either the Control or the SkinBase class. Control is used to define a new control from scratch, while SkinBase is used when creating a custom skin for an existing control.

Extending the Control Class

When extending the Control class, you will need to define the UI of the control by overriding the createDefaultSkin() method. This method is called when the control is initialized and should return an instance of the Skin class that defines the control's visual appearance.

The createDefaultSkin() method returns an instance of the skin class which can be either a custom skin or the default skin. The default skin should be returned if no custom skin is to be defined.

The following code shows an example of creating a custom progress bar control:

import javafx.scene.control.Control;

public class CustomProgressBar extends Control {
    public CustomProgressBar() {
        // Set the preferred width and height
        setPrefSize(150, 30);
    }

    @Override
    public String getUserAgentStylesheet() {
        // Set the default stylesheet for the custom control
        return ProgressBar.class.getResource("resources/custom-progressbar.css").toExternalForm(); //assuming ProgressBar is the control you want to override
    }

    @Override
    protected Skin<?> createDefaultSkin() {
        // Return an instance of the custom ProgressBarSkin
        return new CustomProgressBarSkin(this);
    }
}

In this example, we define a new class called CustomProgressBar that extends the Control class. We set the preferred width and height of the progress bar and override the getUserAgentStylesheet() method to set a default stylesheet for the control.

We also override the createDefaultSkin() method to return a new instance of the CustomProgressBarSkin class that defines the visual appearance of the progress bar control.

import javafx.scene.control.SkinBase;

public class CustomProgressBarSkin extends SkinBase<CustomProgressBar> {
    public CustomProgressBarSkin(CustomProgressBar control) {
        super(control);
        // Set the visual appearance of the progress bar
    }
}

In the stylesheet, we could define the custom styling for the ProgressBar control. For example, we could define the -fx-background-color, -fx-background-radius, -fx-border-color property to give a unique appearance to the control. The CSS support in JavaFX is comprehensive, and you can download and study various CSS snippets and examples in the Oracle documentation for JavaFX.

Extending the SkinBase Class

When extending the SkinBase class, you will need to define the UI of the control in the constructor of the skin class. You will also need to override the getSkinnable() method to return the control instance being skinned.

The following code shows an example of creating a custom skin for the Button control:

import javafx.scene.control.Button;
import javafx.scene.control.SkinBase;

public class CustomButtonSkin extends SkinBase<Button> {
    public CustomButtonSkin(Button control) {
        super(control);
       // Set the visual appearance of the button
    }

    @Override
    protected void layoutChildren(double contentX, double contentY, double contentWidth, double contentHeight) {
        // Define the layout of the button control
    }
}

In this example, we define a new class called CustomButtonSkin that extends the SkinBase class. We set the visual appearance of the button in the constructor of the skin class.

We also override the layoutChildren() method to define the layout of the button control. This method is called whenever the layout of the control is updated.

Styling Custom Controls

Styling a custom control involves creating CSS rules that target the custom control's class, ID, or pseudo-class. In JavaFX, styling a custom control follows the same syntax as styling any other JavaFX control.

Defining the CSS File for a Control

To define the CSS file for a custom control, you will need to create a new file in your project directory and give it a unique name with a .css extension. The CSS file should be located in the src/main/resources directory of your project.

For example, if you create a custom control called CustomButton, you can define its CSS file as follows:

src/main/resources/custom-button.css

Adding Styles to a Custom Control

To add styles to a custom control, you will need to create a CSS rule that targets the custom control's class or ID. You can use either the class or id attribute of the custom control to target it in your CSS file.

Class Selector

To style a custom control using the class selector, you will need to define a unique class for the custom control, and then include the class name in the CSS rule to target it.

.custom-button {
    -fx-background-color: blue;
    -fx-text-fill: white;
}

ID Selector

To style a custom control using the ID selector, you will need to define a unique ID for the custom control, and then include the ID name in the CSS rule to target it.

#custom-button {
    -fx-background-color: blue;
    -fx-text-fill: white;
}

Applying Styles to a Custom Control

To apply styles to a custom control, you will need to include the CSS file in the JavaFX application. You can do this in two ways:

Adding the CSS File to the Scene

To include the CSS file in the JavaFX application, you can add it to the scene object's stylesheet array. The following example shows how to include the custom button's CSS file in the scene:

import javafx.scene.*;
import javafx.scene.control.*;
import javafx.scene.layout.*;
import javafx.application.*;
import javafx.stage.*;
public class App extends Application {
     public void start(Stage stage) {
         //Create a custom button
         CustomButton customButton = new CustomButton();
         Scene scene = new Scene(new StackPane(customButton), 300, 250);
         //Add the stylesheet for the custom button
         scene.getStylesheets().add(getClass().getResource("custom-button.css").toExternalForm());
         stage.setScene(scene);
         stage.show();
     }
}

In this example, we create a new custom button, set its stylesheet using the scene.getStylesheets().add() method, and add it to the scene.

Adding the CSS File to the Control

To add the CSS file to the control, you can override the getUserAgentStylesheet() method in the custom control class.

public class CustomButton extends Button {
    public CustomButton() {
        super("Custom Button");
    }
    @Override
    public String getUserAgentStylesheet() {
        return getClass().getResource("custom-button.css").toExternalForm();
    }
}

In this example, we create a new custom button and override the getUserAgentStylesheet() method to specify the location of the custom button's CSS file.

Conclusion

Custom controls are an excellent way to make your application stand out visually and functionally. By defining the appearance and behavior of your custom controls, you can enrich your application with unique features that are not available with standard JavaFX controls.

In this article, we have explored how to create and style custom controls in JavaFX. We have seen how to extend the Control and SkinBase classes to create controls from scratch or define custom skins for existing controls. Additionally, we have seen how to style custom controls by creating CSS rules that target different elements of the control.

Now that you have an understanding of custom controls in JavaFX, go ahead and experiment with creating your own custom control. With this knowledge, you can design and implement tailored solutions that cater to your specific application needs.

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