Update events from ObjectProperty (just like in ObservableList)

Question

I can use an extractor (Callback<E, Observable[]> extractor) to make a ListProperty fire change events if one of its elements changed one of its properties (update event).

Update Change Event in ObservableList

Is there an equivalent for ObjectProperty<>? I have an SimpleObjectProperty which I want to fire events when properties of it's value (another bean type) change (update change events).

Sample code:

public class TestBean {

    public static <T extends TestBean> Callback<T, Observable[]> extractor() {

    return (final T o) -> new Observable[] { o.testPropertyProperty() };
    }

    private final StringProperty testProperty = new SimpleStringProperty();

    public final StringProperty testPropertyProperty() {
    return this.testProperty;
    }

    public final String getTestProperty() {
    return this.testPropertyProperty().get();
    }

    public final void setTestProperty(final String testProperty) {
    this.testPropertyProperty().set(testProperty);
    }

}

public class SomeType {

    /**
     * How can I listen for changes of TestBean#testProperty?
     */
    private final ObjectProperty<TestBean> property = new SimpleObjectProperty<>();

}

I want to receive change events if the value of SomeType#property changes, but also, if SomeType#property#testProperty changes.

I cannot just listen for SomeType#property#testProperty, since I would not be notified when SomeType#property was changed (I would then listen on the wrong object for changes).

Answer 1

I want to receive change events if value of SomeType#property changes, but also, if SomeType#property#testProperty changes.

I cannot just listen for SomeType#property#testProperty, since I would not be notified, when SomeType#property was changed (I would then listen on the wrong object for changes).

This is a limitation of sorts of the current iteration of JavaFX. The built-in way is unreliable and you're better off using 3rd party libraries. See this answer for more information.

For you case, ReactFX can be utilized in a similar way:

import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;

import org.reactfx.value.Val;
import org.reactfx.value.Var;

class TestBean {

    private final StringProperty testProperty = new SimpleStringProperty();
    public final StringProperty testPropertyProperty()        { return testProperty; }
    public final String getTestProperty()                     { return testProperty.get(); }
    public final void setTestProperty(String newTestProperty) { testProperty.set(newTestProperty); }
}

public class SomeType {

    private final ObjectProperty<TestBean> property = new SimpleObjectProperty<>();
    public final ObjectProperty<TestBean> propertyProperty() { return property; }
    public final TestBean getProperty()                      { return property.get(); }
    public final void setProperty(TestBean newProperty)      { property.set(newProperty); }

    public static void main(String[] args) {
        SomeType someType = new SomeType();
        Var<String> chainedTestProperty = Val.selectVar(someType.propertyProperty(), TestBean::testPropertyProperty);
        chainedTestProperty.addListener((obs, oldVal, newVal) -> System.out.println(obs + " " + oldVal + "->" + newVal));

        //Tests
        someType.setProperty(new TestBean());
        someType.getProperty().setTestProperty("s1");
        TestBean bean2 = new TestBean();
        bean2.setTestProperty("s2");
        someType.setProperty(bean2);
        someType.setProperty(new TestBean());
    }
}

Output:

org.reactfx.value.FlatMappedVar@7aec35a null->s1 
org.reactfx.value.FlatMappedVar@7aec35a s1->s2 
org.reactfx.value.FlatMappedVar@7aec35a s2->null

The key line

Var<String> chainedTestProperty = Val.selectVar(someType.propertyProperty(), TestBean::testPropertyProperty);

is a sort of listener chaining. The first argument is a property (OvservableValue) of some type Type. The second argument is the "sub"-property of some other type Type2 inside Type, which is given as a function from Type to that property.

Now whenever any "links" in the chain change, you are notified. You can continue to listen to changes in sub-sub-... properties by continuously chaining ovservables this way.