在JavaFX中访问GridPane的列索引和行索引时，始终返回null

Question

你好，所以我尝试了许多在线解决方案，如何获得在网格窗格中点击的节点（单元格）。我使用的获取节点的方法如下所示。我也尝试过迭代这个方法之前的所有节点。我已经用场景构建器构建了网格，正如你在下面的图片中看到的，列和行都清楚地存在。我正在尝试这个解决方案如何在鼠标上获得网格窗格行和列ID在JavaFX网格的每个单元格中输入？但是，正如我上面提到的，从行和列返回的值是null。

@FXML
    private void mouseEntered(MouseEvent e) {
        Node source = (Node)e.getSource() ;
        System.out.println(source);
        Integer colIndex = userSelectionGrid.getColumnIndex(source);
        Integer rowIndex = userSelectionGrid.getRowIndex(source);
        if (colIndex == null && rowIndex == null) System.out.println("BOO");
        else
        System.out.printf("Mouse entered cell [%d, %d]%n", colIndex.intValue(), rowIndex.intValue());
    }

包含此网格的FXML

<GridPane fx:id="userSelectionGrid" onMouseClicked="#mouseEntered" prefHeight="44.0" prefWidth="563.0">
         <columnConstraints>
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" />
            <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
         </columnConstraints>
         <rowConstraints>
            <RowConstraints minHeight="10.0" vgrow="SOMETIMES" />
         </rowConstraints>
         <children>
            <Label text="SAVE" GridPane.columnIndex="1" GridPane.halignment="CENTER" GridPane.rowIndex="0">
               <font>
                  <Font name="System Bold" size="13.0" />
               </font>
            </Label>
            <Label text="CANCEL" GridPane.columnIndex="0" GridPane.halignment="CENTER" GridPane.rowIndex="0">
               <font>
                  <Font name="System Bold" size="13.0" />
               </font>
            </Label>
            <Separator orientation="VERTICAL" GridPane.columnIndex="1" />
         </children>
         <VBox.margin>
            <Insets />
         </VBox.margin>
      </GridPane>

Answer 1

事件源是添加处理程序的节点，即在本例中是网格窗格。您可以将处理程序添加到GridPane的子级，以确保源节点的正确性：

<GridPane fx:id="userSelectionGrid" prefHeight="44.0" prefWidth="563.0">
     <columnConstraints>
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" />
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
     </columnConstraints>
     <rowConstraints>
        <RowConstraints minHeight="10.0" vgrow="SOMETIMES" />
     </rowConstraints>
     <children>
        <Label text="SAVE" GridPane.columnIndex="1" GridPane.halignment="CENTER" GridPane.rowIndex="0"  onMouseClicked="#mouseEntered">
           <font>
              <Font name="System Bold" size="13.0" />
           </font>
        </Label>
        <Label text="CANCEL" GridPane.columnIndex="0" GridPane.halignment="CENTER" GridPane.rowIndex="0"  onMouseClicked="#mouseEntered">
           <font>
              <Font name="System Bold" size="13.0" />
           </font>
        </Label>
        <Separator orientation="VERTICAL" GridPane.columnIndex="1" />
     </children>
     <VBox.margin>
        <Insets />
     </VBox.margin>
</GridPane>

请注意，您也可以使用原始的fxml进行此工作。然而，有几件事你应该考虑：

>

if (colIndex == null && rowIndex == null)

过于强大，无法阻止其他部分中的NullPointerExc农田。这可能发生，例如，如果分隔符被单击。

@FXML
private void mouseEntered(MouseEvent e) {
    Node target = (Node) e.getTarget();
    // traverse towards root until userSelectionGrid is the parent node
    if (target != userSelectionGrid) {
        Node parent;
        while ((parent = target.getParent()) != userSelectionGrid) {
            target = parent;
        }
    }
    Integer colIndex = userSelectionGrid.getColumnIndex(target);
    Integer rowIndex = userSelectionGrid.getRowIndex(target);
    if (colIndex == null || rowIndex == null) {
        System.out.println("BOO");
    } else {
        System.out.printf("Mouse entered cell [%d, %d]%n", colIndex.intValue(), rowIndex.intValue());
    }
}

请注意，标签s不会填充整个网格窗格，除非您将首选大小设置为大于网格窗格约束。这会弄乱网格窗格的布局。解决方法是将区域s放置在单元格中标签s的后面。可以使用单元格调整这些节点的大小，而不会影响网格窗格布局，这样可以捕获这些节点上的事件：

<GridPane fx:id="userSelectionGrid" prefHeight="44.0" prefWidth="563.0" onMouseClicked="#mouseEntered">                 
    <columnConstraints>
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" fillWidth="true" />
        <ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" fillWidth="true" />
    </columnConstraints>
    <rowConstraints>
        <RowConstraints minHeight="10.0" vgrow="SOMETIMES" fillHeight="true" />
    </rowConstraints>
    <children>
        <Region GridPane.columnIndex="1" GridPane.rowIndex="0"/>
        <Region GridPane.columnIndex="0" GridPane.rowIndex="0"/>
        <Label text="SAVE" GridPane.columnIndex="1" GridPane.halignment="CENTER" GridPane.rowIndex="0">
            <font>
                <Font name="System Bold" size="13.0" />
            </font>
        </Label>
        <Label text="CANCEL" GridPane.columnIndex="0" GridPane.halignment="CENTER" GridPane.rowIndex="0">
            <font>
                <Font name="System Bold" size="13.0" />
            </font>
        </Label>
        <Separator orientation="VERTICAL" GridPane.columnIndex="1" />
    </children>
    <VBox.margin>
        <Insets />
    </VBox.margin>
</GridPane>