[FIXED] Converting DoubleBinding into double in javaFX

Issue

DoubleBinding angle = new SimpleDoubleProperty(myIndex*Math.PI*2).divide(nrMoons);
moon.centerXProperty().bind(earth.centerXProperty().add(Math.cos(angle.doubleValue()).multiply(RADIUS_ORBIT))); 

that is the part of my code, where I get an error that double angle.doubleValue() cannot be dereferenced, and Math.cos() requires a double not a DoubleBinding, any idea on how to convert it?

Solution

Assuming the quantity you want to add is the product of the cosine of the angle, and RADIUS_ORBIT, you just need to use the operator * instead of the function multiply:

moon.centerXProperty().bind(earth.centerXProperty().add(Math.cos(angle.doubleValue()) * RADIUS_ORBIT));

Note that this probably won't work the way you want: the value you pass to add(...) is not observable (it's just a plain double), so the value will only update if earth.centerXProperty() changes, but won't update if angle changes. This is not so much because of using * instead of multiply(), but because Math.cos() returns a plain double instead of some kind of ObservableDoubleValue. There's no direct API in JavaFX properties/bindings for "taking the cosine of a value".

If you want this to depend dynamically on angle, you should use a custom binding (which also has the advantage of making the computation easier to see in the code).

I think this is the value you want to compute:

moon.centerXProperty.bind(Bindings.createDoubleBinding(() -> {
    double earthCenter = earth.getCenterX();
    double offset = Math.cos(angle.get()) * RADIUS_ORBIT ;
    return earthCenter + offset ;
}, earth.centerXProperty(), angle);

Answered By - James_D