JavaFX: Get Node by row and column

Question

Is there any way to get a specific Node from a gridPane if I know its location (row and column) or any other way to get a node from a gridPane?

Nevanevada

Duplicate of https://mcmap.net/q/469692/-javafx-gridpane-retrieve-specific-cell-content/3110608 – Chiu

Answer 1

I don't see any direct API to get node by row column index, but you can use getChildren API from Pane, and getRowIndex(Node child) and getColumnIndex(Node child) from GridPane

//Gets the list of children of this Parent. 
public ObservableList<Node> getChildren() 
//Returns the child's column index constraint if set
public static java.lang.Integer getColumnIndex(Node child)
//Returns the child's row index constraint if set.
public static java.lang.Integer getRowIndex(Node child)

Here is the sample code to get the Node using row and column indices from the GridPane

public Node getNodeByRowColumnIndex (final int row, final int column, GridPane gridPane) {
    Node result = null;
    ObservableList<Node> childrens = gridPane.getChildren();

    for (Node node : childrens) {
        if(gridPane.getRowIndex(node) == row && gridPane.getColumnIndex(node) == column) {
            result = node;
            break;
        }
    }

    return result;
}

Important Update: getRowIndex() and getColumnIndex() are now static methods and should be changed to GridPane.getRowIndex(node) and GridPane.getColumnIndex(node).

Akkerman

Is there any reason to use java.lang.Integer over the standard? – Delayedaction

Please note that specifying null for the indices is also allowed; in this case the index is treated as 0. In your case this results in a NPE though. – Spies

I think the methods getRowIndex() and getColumnIndex() only return a value if such a constraint has been set on the node i.e. there is no guarantee that these will return the column or row indices. – Lourielouse

@Fabian does this mean that GridPane.getMargin(node) will always return null when the node is the first row in the grid pane? – Incomprehensive

@Incomprehensive I wasn't writing about margin, but GidPane.getMargin(node) will return null, if no margin was set for node, whether it's in the first row or not. – Spies

@Fabian sorry, I meant getRowIndex. I have a scenario where getRowIndex(node) returns null but I expect 0. If I put that same node in any other row, the method returns 1,2,3... – Incomprehensive

Make sure your constraints are set. Scenebuilder likes to treat 0 as not set and nulls the field. So manually set the constraints in the fxml file. e.g <Canvas GridPane.columnIndex=”0” GidPan.rowIndex=”0”>. Also since it's not guaranteed to return a non-null value from getRowIndex/getColumnIndex you should use an Integer object and check for null in the if statement. e.g. if(null != nodeRow && null != nodeCol ... – Efta

Answer 2

The above answer from @invariant is totally correct but for some people that do it that way, there may be performances issues, especially with GridPanes that contain many elements. And also when working with loops (iterating over all the elements of a GridPane).

What I suggest you is to initialize a static array of all your element/nodes contained within the grid pane. Then use this array to get the nodes you need.

i.e.

1. have a double dimensional array :

private Node[][] gridPaneArray = null;

2. Call a method like so during the initialization of your view :

    private void initializeGridPaneArray()
    {
       this.gridPaneArray = new Node[/*nbLines*/][/*nbColumns*/];
       for(Node node : this.mainPane.getChildren())
       {
          this.gridPaneArray[GridPane.getRowIndex(node)][GridPane.getColumnIndex(node)] = node;
       }
    }

3. Get your node

Node n = this.gridPaneArray[x][y]; // and cast it to any type you want/need

Attune