Using API Helpers for Defining Component Properties
The framework provides a helper called PropertyDescriptor
which makes managing attributes and properties in a component easy. You can use PropertyDescriptor
to define the property name and the default value in a single place and use the descriptor from the setter and getter methods:
Java
@Tag("input")
public class TextField extends Component {
private static PropertyDescriptor<String, String> VALUE =
PropertyDescriptors.propertyWithDefault("value", "");
public String getValue() {
return get(VALUE);
}
public void setValue(String value) {
set(VALUE, value);
}
}
In your component API for a given property, e.g. value
of an input field, you want to ensure a couple of things are always true:
The getter and setter use the same property or attribute
The default value is handled properly
The getter return value is either the type used by the setter, e.g.
String
for an inputvalue
or an optional version of it, i.e.Optional<String>
if the property is not mandatory.
PropertyDescriptors will automatically take these points into consideration for you.
PropertyDescriptor
instances are created using the helpers available in the PropertyDescriptors
class. There are different helper methods depending on how you want your property to work:
PropertyDescriptors.propertyWithDefault
for mapping to an element property with a given default valuePropertyDescriptors.attributeWithDefault
for mapping to an element attribute with a given default valuePropertyDescriptors.optionalAttributeWithDefault
for mapping to an element attribute with a given default value but returning an emptyOptional
when the default value is set
You can use the optionalAttributeWithDefault
e.g. for a placeholder
in a TextField as the placeholder is not mandatory:
Java
@Tag("input")
public class TextField extends Component {
private static PropertyDescriptor<String, Optional<String>> PLACEHOLDER =
PropertyDescriptors.optionalAttributeWithDefault("placeholder", "");
public Optional<String> getPlaceholder() {
return get(PLACEHOLDER);
}
public void setPlaceholder(String placeholder) {
set(PLACEHOLDER, placeholder);
}
}
Note | The default value used in the PropertyDescriptors methods should match what the value becomes in the browser when the attribute or property is not set. Otherwise the value will not be correctly sent to the browser when the user sets the value to the default value. |