---
title: Composite Fields with CustomField
order: 34
layout: page
---

[[components.customfield]]
= Composite Fields with CustomField

The [classname]#CustomField# is a way to create composite components as with [classname]#CustomComponent#, except that it implements the [interfacename]#Field# interface and inherits [classname]#AbstractField#, described in <<dummy/../../../framework/components/components-fields#components.fields,"Field Components">>.
A field allows editing a property value in the data model, and can be bound to data with [classname]#Binder#, as described in <<dummy/../../../framework/datamodel/datamodel-forms#datamodel.forms, "Binding Data to Forms">>.

A composite field class must implement [methodname]#initContent()# method.
It should return the content composite of the field.

Methods overriding
[methodname]#setInternalValue()# should call the superclass method.

[[components.customfield.basic]]
== Basic Use

Let us consider a simple custom switch button component that allows you to click a button to switch it "on" and "off", as illustrated in <<figure.components.customfield.basic>>.

[[figure.components.customfield.basic]]
.A custom switch button field
image::img/customfield-basic.png[width=25%, scaledwidth=40%]

The field has [classname]#Boolean# value type, which the [methodname]#getType()# returns.
In [methodname]#initContent()#, we initialize the button and the layout.
Notice how we handle user interaction with the button to change the field value.
We customize the [methodname]#setValue()# method to reflect the state back to the user.

[source, Java]
----
public class BooleanField extends CustomField<Boolean> {
    private final Button button = new Button("Off");
    private boolean value;

    @Override
    protected Component initContent() {
        button.addClickListener(event -> {
            setValue(!getValue());
            button.setCaption(getValue() ? "On" : "Off");
        });

        VerticalLayout layout = new VerticalLayout();
        layout.addComponent(new Label("Click the button"));
        layout.addComponent(button);
        return layout;
    }

    @Override
    public Boolean getValue() {
        return value;
    }

    @Override
    protected void doSetValue(Boolean value) {
        this.value = value;
        button.setCaption(value ? "On" : "Off");
    }
}
----

We can now use the field in all the normal ways for a field:

[source, Java]
----
// Create it
BooleanField field = new BooleanField();

// It's a field so we can set its value
field.setValue(new Boolean(true));

// ...and read the value
Label value = new Label(field.getValue()?
    "Initially on" : "Initially off");

// ...and handle value changes
field.addValueChangeListener(event ->
    value.setValue(field.getValue()?
        "It's now on" : "It's now off"));
----