What Bindings are for?

Bindings provide a way to keep properties synchronized (in one, or both ways).
If the dependency is one-way, we call it 'binding' (A property is bound to another).
If the dependency is both-ways, we call it 'synchronization' (A property is synchronized with another).

 

How do I use Bindings?

1. A property of a view (such as its value or colour) might be bound to a value of a property of a model object (such as a price or an overdue flag).

 

// RWProperty is a property which can be read, written, and observed for value changes.
RWProperty viewValue = new ValueHolder(INITIAL_VIEW_VALUE);
RWProperty modelValue = new ValueHolder(INITIAL_MODEL_VALUE);
// initialize view value with model's value, and keep it bound to modelValue
Bindings.bind(modelValue, viewValue);

 

2. The value displayed in a text field might be kept synchronised with the first name of a Person object.

 

class Person {
public RWProperty name;
public RWProperty surname;
...
}
RWProperty textFieldValue = new ValueHolder(INITIAL_TEXT_FIELD_VALUE);
RWProperty personValue = new ValueHolder(INITIAL_PERSON_VALUE);
// initializes both properties with INITIAL_VALUE, and keeps them synchronized
Bindings.synchronize(textFieldValue, personValue.name, INITIAL_VALUE);

 

3. A property can observe another and calculate its value based on the current value of the observed property

 

RWProperty currentPerson = ...
// ObservableProperty can be read and observed for changes.
ObservableProperty currentPersonNameStartsWithA = new AbstractTransformProperty(currentPerson) {
@Override
protected Boolean transform(Person value) {
return value.name.get().charAt(0) == 'A';
}
};

 

4. Boolean properties can be easily combined into complex expressions

 

ObservableProperty p1 = ...
ObservableProperty p2 = ...
ObservableProperty p3 = ...
ObservableProperty p4 = ...
ObservableProperty pv = new AllTrue( new AnyTrue(p1, p2), new Not(p3), p4 );