CODEWITHSUNDEEP
javajavafx-8
BenK
BenK

Reputation: 333

GridPane getRowIndex returns null after second use

I am making a Lights Out game in JavaFX. I have a BoardController class with an initializer method that adds Squares to a GridPane member board. This method calls another method that sets a mouse event listener on each Square.

In the event handler, I use GridPane.getRowIndex and GridPane.getColumnIndex. Then I need to get a node by its GridPane coordinates which I do in a function the handler calls. But there, GridPane.getRowIndex and GridPane.getColumnIndex return null. Why? How do I fix this?

Here's the code.

//set mouse handler on each square
private void setMouseHandlers()
{
    ObservableList<Node> children = board.getChildren();
    for(Node child : children)
      child.setOnMouseClicked(new EventHandler() {

        @Override
        public void handle(Event event) {
            int row = GridPane.getRowIndex(child);    //fine
            int col = GridPane.getColumnIndex(child); //fine

            int up_row = row-1;
            int down_row = row+1;
            int left_col = col-1;
            int right_col = col+1;

            toggleNodeColor((Shape)child);

            //this expression works but getrow/col index does not work in the next function calls even if I pass the children vector
            //System.out.println(GridPane.getRowIndex(child) + " " + GridPane.getColumnIndex(child));

            if(isInBounds(up_row,col))    toggleNodeColor((Shape) getNodeInGrid(up_row,col));
            if(isInBounds(down_row,col))  toggleNodeColor((Shape) getNodeInGrid(down_row,col));
            if(isInBounds(row,left_col))  toggleNodeColor((Shape) getNodeInGrid(row,left_col));
            if(isInBounds(row,right_col)) toggleNodeColor((Shape) getNodeInGrid(row,right_col));

        }
}

And here is getNodeInGrid:

private Node getNodeInGrid(final int row, final int col)
{
    Node result = null;
    ObservableList<Node> children = board.getChildren();
    for(Node child : children)
    {
        //FIXME these row/col idxs are all null even though the exact same code works in the setMouseHandlers() method
        if( (GridPane.getRowIndex(child) == row) && (GridPane.getColumnIndex(child) == col))  //NullPointer at this line
            {
                result = child;
                break;
            }
    }
    return result;
}

Upvotes: 1

Views: 881

Answers (1)

BenK
BenK

Reputation: 333

I've found the problem.

Printing out the result of gridPane.getRowindex(child)==null reveals that there is a "ghost child," one I did not add to the GridPane myself. Since I didn't add it, getRowIndex returns null on it because it never had its row and column set.

The quick 'n dirty fix is to add a check in GetNodeInGrid().

Upvotes: 1

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