When I run the following code in the start method of my Main (JavaFX) class I get weird results. The window gets displayed but pane
(with a green border) has a width of 0. It is supposed to have the same width as the container's height since I binded prefWidth to the height property.
Then, when I resize the window, the binding comes into effect and the pane becomes a square. Notice that if I maximize the window it also doesn't apply the bindings.
Thank you!
//Create a pane with a min width of 10 and a green border to be able to see it
Pane pane = new Pane();
pane.setStyle("-fx-border-color: green; -fx-border-width: 2");
//Bind the pane's preferred width to the pane's height
pane.prefWidthProperty().bind(pane.heightProperty());
//Put the pane in a vbox that does not fill the stage's width and make the pane grow in the vbox
VBox container = new VBox(pane);
container.setFillWidth(false);
VBox.setVgrow(pane, Priority.SOMETIMES);
//Show the vbox
primaryStage.setScene(new Scene(container, 600, 400));
primaryStage.show();
The problem you are running into here is that when the container is laid out, it has no reasonable information as to the order in which it should compute the width and the height of the
pane
. So essentially what happens is it computes the width, which (since it's empty), is zero; then computes the height (which fills the container, since you told theVBox
to do that). After that, theprefWidth
property is changed, but by then the actual width has already been set, so it's essentially too late. The next time a layout pass occurs, the new pref width is taken into account.I haven't checked the actual layout code, but (since the default content bias is null) most likely the layout code for the vbox is going to do something equivalent to the following pseudocode:
The last call actually causes the height of the pane to change, which then causes the
prefWidth
to change via the binding. Of course, that's too late for the current layout pass, which has already set the width based on the previous preferred width calculation.Basically, relying on bindings to manage layout like this is not a reliable way of doing things, because you are changing properties (such as
prefWidth
in this example) during the layout pass, when it may be already too late to resize the component.The reliable way to manage layout for a pane like this is to override the appropriate layout methods, which are invoked by the layout pass in order to size the component.
For this example, since the width depends on the height, you should return
VERTICAL
for thecontentBias
, and you should overridecomputePrefWidth(double height)
to return the height (so the width is set to the height):