| Even if I always kept the TextFlow as a graphic on the cells, I would need to change its children to show the correct shape and text. So there would normally be changes to the children when updateItem is called, just one level deeper in the node hierarchy.
It makes sense that in most circumstances you shouldn’t be adding or removing nodes during layout, but if updateItem is called during layout it would have to be an exception. As you note, updating the graphic is normal and clearly changes the children. I was surprised that I had to call applyCss() one level higher in the node hierarchy than where the relevant CSS actually was, but I’m okay with that as a workaround for now. I don’t expect it to be a performance issue.
Scott On Feb 22, 2023, at 1:03 AM, John Hendrikx <john.hendr...@gmail.com> wrote:
It's a bit hard to say if this is a bug or not.
I think this happens any time when children are added during
layout. Most controls will avoid doing this, but when Cells are
involved, there is another layer of indirection. I think the View
classes manage their cells during layout, and since Cells can be
newly created or the Cells are modified in ways that would trigger
a child to be added/removed, then this effectively is changing the
children list during layout.
For example, Labels, when you add a graphic, immediately update
their children list to include the graphic. Normally, calling
`setGraphic` is not done by you during layout but in an event
listener or during creation of the control. However, when it is
called in `Cell#updateItem` then layout is running, and the Label
will change its children list when it notices the graphic
changed. This new child won't have CSS applied yet.
I couldn't find documentation that says you shouldn't add/remove
children during layout, but I'm pretty sure this is standard
practice.
The View controls may or may not be creating cells during layout,
but they are almost certain to call `updateItem` on cells during
layout. I'm not certain if this could be avoided in a similar
fashion as I've done for my own ListView skin (using the pulse
listener); if it can be, then this could be a bug fix. If it
can't, then I think `Cell#updateItem` should mention that the call
should not modify the children list directly or indirectly.
As I pointed out in my other reply, you may be able to set a
dummy graphic on all cells, and just hide it when it is not
needed.
--John
On 22/02/2023 02:26, Scott Palmer wrote:
Well
I managed to work around it by placing the applyCss() call on
the Cell itself, rather than the Shape node that I was
styling. I'm still not sure if I'm doing something wrong, if
this is just how it's done and the applyCss() call is the
correct thing to do for this case, or if this should be
considered a bug.
Scott
I agree, this seems
like it could be the same issue. Could you give me a
little more context as to how this code works? I'm not
implementing my own skin (maybe I should, I've never tried
that before). Is this something I can trigger without a
custom skin?
Regards,
Scott.
I've run into something similar, maybe even the same
issue.
My issue was that modifying the list of cell children
(in a Skin for ListView) caused a 1 frame white
flicker (my application is black, so it was annoying)
because no CSS was applied yet to those newly added
children. This occured when the ListView first only
had a few children and wasn't completely filled, and
then switching to a list which required more cells to
be created. I couldn't find a "correct" place to
modify the list of children that would avoid the
flicker (layoutChildren/computePrefWidth are places I
tried).
In the end I did this, and added a comment to remind
me why the hack was there:
/*
* A pre-layout pulse listener is added to the
current Scene to manage the
* cells before the CSS pass occurs (this could
also be done with an AnimationTimer).
*
* If cells are not managed before the CSS pass,
new cells will be rendered for
* one frame without CSS applied. This results in
a visual artifact (a white flash
* for example if the background is supposed to be
dark, while white is the default
* color without any CSS applied).
*/
private final Runnable pulseListener = () -> {
int lines = vertical ? visibleColumns.get() :
visibleRows.get();
int firstIndex = (int)(scrollPosition.get()) *
lines;
content.manageCells(firstIndex);
};
Now, the reason I think this may be same issue is
that you're also doing a modification of the children
list during layout: setting the graphic is sort of
equivalent to label.getChildren().add(graphic)
--John
On 20/02/2023 20:58, Scott Palmer wrote:
I'm seeing an
odd issue with using CSS to colour a Shape when I
have it as a child of a TextFlow.
My use case
is a "rich" text Cell in a tree or list. I want
to have the text portion in multiple colours and
so instead of using the graphic and text parts of
a typical Cell, I'm using only the Graphic and
setting it to a TextFlow to get the text colours.
This means that I lose the ability to set a
graphic independen to the text, and so the
graphic is also added to the TextFlow.
To style the
graphics, which are made of simple shapes, I'm
using CSS. It makes it easy to adapt the colours
for when a cell is selected etc. What I've
noticed is that as the cell selection moves around
the Shape component of the TextFlow flickers, as
if it is drawn first using default colours and
then the CSS is applied afterward. I
tried working around this by explicitly calling
applyCss() on the Shape from the Cell's update
method, but it did not help. If I explicitly set
the Stroke and Fill via the Shape API the
flickering does not occur. If I use CSS, but set
the Shape as the Cell's graphic and resort to only
having plain text, there is no flickering.
A test
program that demonstrates this is below.
Bug or known
limitation?
Scott
------------------------------------
package bugs;
import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.CheckBox;
import javafx.scene.control.ContentDisplay;
import javafx.scene.control.Label;
import javafx.scene.control.ListCell;
import javafx.scene.control.ListView;
import javafx.scene.control.Tab;
import javafx.scene.control.TabPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Rectangle;
import javafx.scene.shape.Shape;
import javafx.scene.text.Text;
import javafx.scene.text.TextFlow;
import javafx.stage.Stage;
public class CSSFlickerInTextFlow extends
Application {
public static void main(String[] args) {
launch(args);
}
private CheckBox onlyCssCB;
@Override
public void start(Stage stage) throws
Exception {
ListView<String> list1 = new
ListView<>();
ListView<String> list2 = new
ListView<>();
var items1 = list1.getItems();
var items2 = list2.getItems();
for (int i = 1; i < 23; i++) {
var x = "Item #"+i;
items1.add(x);
items2.add(x);
}
list1.setCellFactory(t -> new
MyCell1());
list2.setCellFactory(t -> new
MyCell2());
_onlyCssCB_ = new CheckBox("Use only CSS
(shapes will flicker in TextFlow)");
HBox buttons = new HBox(8, onlyCssCB);
buttons.setPadding(new Insets(4));
Tab custom = new Tab("Everything in
Graphic", list1);
Tab withoutColoredText = new Tab("Graphic
+ Text", list2);
TabPane tabs = new TabPane(custom,
withoutColoredText);
VBox root = new VBox(
new Label("""
Focus in list, cursor up
and down, pay attention to the circle.
Try the same with the
box checked - circle flickers.
Doesn't happen when not
using the TextFlow.
"""),
buttons, tabs);
root.setPadding(new Insets(4));
var scene = new Scene(root);
stage.setScene(scene);
stage.setTitle("Flickering with CSS in
TextFlow");
stage.show();
}
private Shape makeGraphic() {
Shape graphic = new Circle(6);
if (!onlyCssCB.isSelected()) {
graphic.setFill(Color.SALMON); // CSS
overrides these but causes flickering if not the
same
graphic.setStroke(Color.BLACK);
}
graphic.setStyle("-fx-fill: salmon;
-fx-stroke: black;");
return graphic;
}
class MyCell1 extends ListCell<String> {
@Override
protected void updateItem(String item,
boolean empty) {
super.updateItem(item, empty);
setContentDisplay(ContentDisplay.GRAPHIC_ONLY);
setText(null);
if (!empty && item != null) {
TextFlow flow = new TextFlow();
Shape graphic = makeGraphic();
graphic.setTranslateY(2);
var nodeList = flow.getChildren();
Text name = new Text(item + " :
");
name.setStyle("-fx-fill:
-fx-text-background-color;");
Text extra = new Text("with
Color");
extra.setStyle("-fx-fill:ladder(-fx-background,
white 49%, salmon 50%);");
nodeList.add(graphic);
nodeList.add(new Rectangle(4,0));
// gap
nodeList.add(name);
nodeList.add(extra);
setGraphic(flow);
} else {
setGraphic(null);
}
}
}
class MyCell2 extends ListCell<String> {
@Override
protected void updateItem(String item,
boolean empty) {
super.updateItem(item, empty);
if (!empty && item != null) {
setGraphic(makeGraphic());
setText(item);
} else {
setText(null);
setGraphic(null);
}
}
}
}
|
