✨ Implement layout hooks for cells

♻️ Refactor layout methods in helpers to accept Cell objects rather than Nodes

Signed-off-by: palexdev <alessandro.parisi406@gmail.com>

src/main/java/io/github/palexdev/virtualizedfx/cells/Cell.java

@@ -73,7 +73,15 @@ public interface Cell<T> {
 	 */
 	void updateItem(T item);
 
-	// TODO implement layout hooks
+	/**
+	 * The system automatically calls this before the cell is laid out.
+	 */
+	default void beforeLayout() {}
+
+	/**
+	 * The system automatically calls this after the cell is laid out.
+	 */
+	default void afterLayout() {}
 
 	/**
 	 * Virtualized containers that make use of a cache to store unneeded cells that may be required again in a second time

src/main/java/io/github/palexdev/virtualizedfx/grid/VFXGridHelper.java

@@ -161,13 +161,13 @@ default Position getViewportPosition() {
 	}
 
 	/**
-	 * Lays out the given node.
+	 * Lays out the given cell.
 	 * The row and column layout indexes are necessary to identify the position of a cell among the others
 	 * (comes before/after, above/below).
 	 *
 	 * @see VFXGridSkin#layout()
 	 */
-	void layout(int rowLayoutIndex, int columnLayoutIndex, Node node);
+	void layout(int rowLayoutIndex, int columnLayoutIndex, Cell<T> cell);
 
 	/**
 	 * @return the total size of each cell, given by the {@link VFXGrid#cellSizeProperty()} summed to the horizontal and
@@ -599,12 +599,15 @@ public ReadOnlyObjectProperty<Position> viewportPositionProperty() {
 		 * {@code totalCellHeight * rowIndex}, the width and height are given by the {@link VFXGrid#cellSizeProperty()}.
 		 */
 		@Override
-		public void layout(int rowLayoutIndex, int columnLayoutIndex, Node node) {
+		public void layout(int rowLayoutIndex, int columnLayoutIndex, Cell<T> cell) {
+			Node node = cell.toNode();
 			double x = getTotalCellSize().getWidth() * columnLayoutIndex;
 			double y = getTotalCellSize().getHeight() * rowLayoutIndex;
 			double w = grid.getCellSize().getWidth();
 			double h = grid.getCellSize().getHeight();
+			cell.beforeLayout();
 			node.resizeRelocate(x, y, w, h);
+			cell.afterLayout();
 		}
 
 		@Override

src/main/java/io/github/palexdev/virtualizedfx/grid/VFXGridSkin.java

@@ -7,7 +7,6 @@
 import io.github.palexdev.virtualizedfx.cells.Cell;
 import javafx.geometry.Insets;
 import javafx.geometry.Orientation;
-import javafx.scene.Node;
 import javafx.scene.Parent;
 import javafx.scene.layout.Pane;
 import javafx.scene.shape.Rectangle;
@@ -172,7 +171,7 @@ protected void addListeners() {
 	 * managed for the {@link VFXGrid}. In other words, it doesn't matter whether our range is [1, 5] or [4, 6] or whatever,
 	 * the layout index will always start from 0 and increment towards the end of the range.
 	 * <p>
-	 * The layout is performed by {@link VFXGridHelper#layout(int, int, Node)}, the two aforementioned counters are passed
+	 * The layout is performed by {@link VFXGridHelper#layout(int, int, Cell)}, the two aforementioned counters are passed
 	 * as arguments.
 	 * <p></p>
 	 * <pre>
@@ -202,7 +201,7 @@ protected void layout() {
 				for (Integer cIdx : state.getColumnsRange()) {
 					int linear = GridUtils.subToInd(nColumns, rIdx, cIdx);
 					if (linear >= grid.size()) break outer_loop;
-					helper.layout(i, j, cells.get(linear).toNode());
+					helper.layout(i, j, cells.get(linear));
 					j++;
 				}
 				i++;

src/main/java/io/github/palexdev/virtualizedfx/list/VFXListHelper.java

@@ -127,12 +127,12 @@ default Position getViewportPosition() {
 	double computeSize(Node node);
 
 	/**
-	 * Lays out the given node. The index parameter is necessary to identify the position of a cell compared to the others
+	 * Lays out the given cell. The index parameter is necessary to identify the position of a cell compared to the others
 	 * (comes before or after).
 	 *
-	 * @param absIndex the absolute index of the given node/cell, see {@link VFXListSkin#layout()}
+	 * @param layoutIndex the absolute index of the given node/cell, see {@link VFXListSkin#layout()}
 	 */
-	void layout(int absIndex, Node node);
+	void layout(int layoutIndex, Cell<T> cell);
 
 
 	/**
@@ -424,11 +424,14 @@ public double computeSize(Node node) {
 		 * computed by {@link #computeSize(Node)}, and the height is given by the {@link VFXList#cellSizeProperty()}.
 		 */
 		@Override
-		public void layout(int absIndex, Node node) {
-			double y = getTotalCellSize() * absIndex;
+		public void layout(int layoutIndex, Cell<T> cell) {
+			Node node = cell.toNode();
+			double y = getTotalCellSize() * layoutIndex;
 			double w = computeSize(node);
 			double h = list.getCellSize();
+			cell.beforeLayout();
 			node.resizeRelocate(0, y, w, h);
+			cell.afterLayout();
 		}
 
 		@Override
@@ -611,11 +614,14 @@ public double computeSize(Node node) {
 		 * computed by {@link #computeSize(Node)}, and the width is given by the {@link VFXList#cellSizeProperty()}.
 		 */
 		@Override
-		public void layout(int absIndex, Node node) {
-			double x = getTotalCellSize() * absIndex;
+		public void layout(int layoutIndex, Cell<T> cell) {
+			Node node = cell.toNode();
+			double x = getTotalCellSize() * layoutIndex;
 			double w = list.getCellSize();
 			double h = computeSize(node);
+			cell.beforeLayout();
 			node.resizeRelocate(x, 0, w, h);
+			cell.afterLayout();
 		}
 
 		@Override

src/main/java/io/github/palexdev/virtualizedfx/list/VFXListSkin.java

@@ -6,7 +6,6 @@
 import io.github.palexdev.virtualizedfx.cells.Cell;
 import javafx.beans.InvalidationListener;
 import javafx.geometry.Orientation;
-import javafx.scene.Node;
 import javafx.scene.layout.Pane;
 import javafx.scene.shape.Rectangle;
 
@@ -166,7 +165,7 @@ protected void addListeners() {
 	 * The loop on the cells uses an external {@code i} variable that tracks the iteration count. This is because cells in the
 	 * state are already ordered by their index (since the state uses a {@link TreeMap}), and the layout is 'absolute'.
 	 * Meaning that the index of the cell is irrelevant for its position, we just care about which comes before/after.
-	 * The layout is performed by {@link VFXListHelper#layout(int, Node)}, the index given to that method is the
+	 * The layout is performed by {@link VFXListHelper#layout(int, Cell)}, the index given to that method is the
 	 * {@code i} variable.
 	 * <p></p>
 	 * <pre>
@@ -190,7 +189,7 @@ protected void layout() {
 		if (state != VFXListState.EMPTY) {
 			int i = 0;
 			for (C cell : state.getCellsByIndex().values()) {
-				helper.layout(i, cell.toNode());
+				helper.layout(i, cell);
 				i++;
 			}
 			onLayoutCompleted(true);

src/main/java/io/github/palexdev/virtualizedfx/table/VFXTableHelper.java

@@ -12,6 +12,7 @@
 import io.github.palexdev.mfxcore.observables.OnInvalidated;
 import io.github.palexdev.mfxcore.observables.When;
 import io.github.palexdev.mfxcore.utils.NumberUtils;
+import io.github.palexdev.virtualizedfx.cells.Cell;
 import io.github.palexdev.virtualizedfx.cells.TableCell;
 import io.github.palexdev.virtualizedfx.enums.ColumnsLayoutMode;
 import io.github.palexdev.virtualizedfx.utils.Utils;
@@ -192,16 +193,18 @@ default void layoutRow(int layoutIdx, VFXTableRow<T> row) {
 		double w = getVirtualMaxX();
 		double h = getTable().getRowsHeight();
 		double y = layoutIdx * h;
+		row.beforeLayout();
 		row.resizeRelocate(0, y, w, h);
+		row.afterLayout();
 	}
 
 	/**
-	 * Lays out the given node/cell.
+	 * Lays out the given cell.
 	 * The layout index is necessary to identify the position of a cell among the others (comes before/after).
 	 *
 	 * @see VFXTableRow#layoutCells()
 	 */
-	boolean layoutCell(int layoutIdx, Node node);
+	boolean layoutCell(int layoutIdx, TableCell<T> cell);
 
 	/**
 	 * Determines and sets the ideal width for the given column, where 'ideal' means that
@@ -713,15 +716,18 @@ public boolean layoutColumn(int layoutIdx, VFXTableColumn<T, ?> column) {
 		 * @return always true
 		 */
 		@Override
-		public boolean layoutCell(int layoutIdx, Node node) {
+		public boolean layoutCell(int layoutIdx, TableCell<T> cell) {
 			VFXTable<T> table = getTable();
 			IntegerRange columnsRange = columnsRange();
 			int colIndex = columnsRange.getMin() + layoutIdx;
 			VFXTableColumn<T, ? extends TableCell<T>> column = table.getColumns().get(colIndex);
+			Node node = cell.toNode();
 			double x = getColumnPos(layoutIdx, column);
 			double w = getColumnWidth(column);
 			double h = table.getRowsHeight();
+			cell.beforeLayout();
 			node.resizeRelocate(x, 0, w, h);
+			cell.afterLayout();
 			return true;
 		}
 
@@ -1152,13 +1158,20 @@ public boolean layoutColumn(int layoutIdx, VFXTableColumn<T, ?> column) {
 		 * the corresponding column, the width, positions and visibility computations are already done when invoking
 		 * {@link #layoutColumn(int, VFXTableColumn)}. Obviously, to do so, we first need to get the cell's corresponding
 		 * column from {@link VFXTable#getColumns()} by the given index.
+		 * <p></p>
+		 * Note: the pre/post layout hooks defined by {@link Cell} are called even if the cell will only be set to
+		 * hidden. This allows implementations to perform actions depending on the visibility state without relying on
+		 * listeners.
 		 */
 		@Override
-		public boolean layoutCell(int layoutIdx, Node node) {
+		public boolean layoutCell(int layoutIdx, TableCell<T> cell) {
 			ObservableList<VFXTableColumn<T, ? extends TableCell<T>>> columns = table.getColumns();
 			VFXTableColumn<T, ? extends TableCell<T>> column = columns.get(layoutIdx);
+			Node node = cell.toNode();
+			cell.beforeLayout();
 			if (!isInViewport(column)) {
 				node.setVisible(false);
+				cell.afterLayout();
 				return false;
 			}
 			double w = getColumnWidth(column);
@@ -1167,6 +1180,7 @@ public boolean layoutCell(int layoutIdx, Node node) {
 			if (node.isVisible() && node.getLayoutX() == x && node.getLayoutBounds().getWidth() == w) return false;
 			node.resizeRelocate(x, 0, w, h);
 			node.setVisible(true);
+			cell.afterLayout();
 			return true;
 		}