Replace a node at (row,col) in a JavaFX GridPane

Question

I am making a grid-style game/simulation based on bugs "sensing" and eating food. I am using a gridPane (called worldGrid) of labels to show the grid of bugs and food. This is obviously going to be constantly updated when a bug moves cells towards food etc.

I currently have a function updateGrid(int col, int row, String cellContent) which I want to replace the label at [row,col] with a label that has the new text in cellContent.

I have the follow which works

worldGrid.add(new Label(cellContent), row,col);

however im worried that that is just adding a label on top of the current label and obviously over 100 iterations of the simulation thats not ideal.

I have tried this before adding the label:

worldGrid.getChildren().remove(row,col);

However I then get an IllegalArgumentException when trying to do the add line.

Any ideas on how to do this? Or even better, any ideas on how best to show a constantly changing grid that will eventually use sprites instead of text?

Answer 1

The col/row provided by grid.add(node, col, row) (ATTENTION first comes col!) is only a layout constraint. This does not provide any means to access columns or rows like slots in a 2-dimensional array. So to replace a node, you have to know its object itself, e.g. remember them in a separate array.

Then you are able to call getChildren().remove(object)... e.g.:

GridPane grid = new GridPane();

Label first = new Label("first");
Label second = new Label("second");

grid.add(first,  1,  1);
grid.add(second,  2,  2);
second.setOnMouseClicked(e -> {
    grid.getChildren().remove(second);
    grid.add(new Label("last"), 2, 2);
});
box.getChildren().addAll(grid);

Answer 2

I agree with Jens-Peter but I would add that you can use GridPane's getColumnIndex and getRowIndex to obtain a particular node's location.

For example ( this is in a component which extends GridPane ):

// set the appropriate label
for (Node node : getChildren()) {
    if (node instanceof Label
     && getColumnIndex(node) == column
     && getRowIndex(node) == row) {
        ((Label)node).setTooltip(new Tooltip(tooltip));
    }
}

in other words, go through all the nodes in the GridPane and check for a match of the conditions you want, in this case row and column.

Answer 3

You called getChildren().remove() method directly will cause the gridpane to go out of sync with the constraints. When you add, it also setup the constraint for the node. Add clearConstraints() method.