CODEWITHSUNDEEP
javagenericsjavafx
DailyFrankPeter
DailyFrankPeter

Reputation: 414

JavaFX & Generics - observing a property of Node which is an ObservableValue

Given a property of a JavaFX Node declared as:

public final ReadOnlyObjectProperty<Bounds> boundsInParentProperty

...which is an ObservableValue<Bounds>. And a method implemented in corresponding ChangeListener<Bounds>:

public void changed(ObservableValue<? extends Bounds> observedValue, Bounds oldvalue, Bounds newvalue)

What is the first argument in the method for?

At first I used observedValue.getValue(), but later I was able to calculate the delta of various coordinates of Bounds from just the second and third argument (newvalue - oldvalue). The type of argument is known (Bounds), so it's not like a key-value scheme. I'm highly distrustful of what I don't understand, so what is this 'observedValue' and should I use it?

EDIT: After the comments I understand it's used for determining which ObservableValue (if multiple) is the source of the event. Let's say I want to have a Line drawn between two draggable Nodes on screen, and I want to track the Bounds of both this way. How to determine which Node is the source of change event (get its reference)?

Upvotes: 0

Views: 302

Answers (1)

Dmitry Zvorygin
Dmitry Zvorygin

Reputation: 477

Sometimes you subscribe your listener to multiple variables change, and you may be interested which one of them had changed. It's quite popular trick in Observer implementation.

Upvotes: 0

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