java - JavaFX：如何通过一条线连接两个节点？

Question

我想将两个Nodes 与 a连接Line（从第一个的中心到第二个的中心）。

初步想法：

• 假设两个节点都存在于场景图中的某处
• Line充当装饰者，不应该被挑选
• 如果有Node Bounds变化，Line应该更新

看起来我需要一些复合属性绑定，包括正确的坐标空间转换。

如何做到这一点？谁能指出一个方向？

Answer 1

此响应中的代码基于问题的答案：CubicCurve JavaFX

下面的示例：

• 假设所有涉及的节点都是兄弟节点。
• 通过在线上调用setMouseTransparent(true)确保连接线不可拾取。
• 在拖动锚节点时自动更新线以连接两个锚节点的中心。

import javafx.application.Application;
import javafx.beans.property.*;
import javafx.event.EventHandler;
import javafx.scene.*;
import javafx.scene.input.MouseEvent;
import javafx.scene.paint.Color;
import javafx.scene.shape.*;
import javafx.stage.Stage;

/** Example of dragging anchors around to manipulate a line. */
public class LineManipulator extends Application {
  public static void main(String[] args) throws Exception { launch(args); }
  @Override public void start(final Stage stage) throws Exception {
    DoubleProperty startX = new SimpleDoubleProperty(100);
    DoubleProperty startY = new SimpleDoubleProperty(100);
    DoubleProperty endX   = new SimpleDoubleProperty(300);
    DoubleProperty endY   = new SimpleDoubleProperty(200);

    Anchor start    = new Anchor(Color.PALEGREEN, startX, startY);
    Anchor end      = new Anchor(Color.TOMATO,    endX,   endY);

    Line line = new BoundLine(startX, startY, endX, endY);
    stage.setTitle("Line Manipulation Sample");
    stage.setScene(new Scene(new Group(line, start, end), 400, 400, Color.ALICEBLUE));
    stage.show();
  }

  class BoundLine extends Line {
    BoundLine(DoubleProperty startX, DoubleProperty startY, DoubleProperty endX, DoubleProperty endY) {
      startXProperty().bind(startX);
      startYProperty().bind(startY);
      endXProperty().bind(endX);
      endYProperty().bind(endY);
      setStrokeWidth(2);
      setStroke(Color.GRAY.deriveColor(0, 1, 1, 0.5));
      setStrokeLineCap(StrokeLineCap.BUTT);
      getStrokeDashArray().setAll(10.0, 5.0);
      setMouseTransparent(true);
    }
  }

  // a draggable anchor displayed around a point.
  class Anchor extends Circle { 
    Anchor(Color color, DoubleProperty x, DoubleProperty y) {
      super(x.get(), y.get(), 10);
      setFill(color.deriveColor(1, 1, 1, 0.5));
      setStroke(color);
      setStrokeWidth(2);
      setStrokeType(StrokeType.OUTSIDE);

      x.bind(centerXProperty());
      y.bind(centerYProperty());
      enableDrag();
    }

    // make a node movable by dragging it around with the mouse.
    private void enableDrag() {
      final Delta dragDelta = new Delta();
      setOnMousePressed(new EventHandler<MouseEvent>() {
        @Override public void handle(MouseEvent mouseEvent) {
          // record a delta distance for the drag and drop operation.
          dragDelta.x = getCenterX() - mouseEvent.getX();
          dragDelta.y = getCenterY() - mouseEvent.getY();
          getScene().setCursor(Cursor.MOVE);
        }
      });
      setOnMouseReleased(new EventHandler<MouseEvent>() {
        @Override public void handle(MouseEvent mouseEvent) {
          getScene().setCursor(Cursor.HAND);
        }
      });
      setOnMouseDragged(new EventHandler<MouseEvent>() {
        @Override public void handle(MouseEvent mouseEvent) {
          double newX = mouseEvent.getX() + dragDelta.x;
          if (newX > 0 && newX < getScene().getWidth()) {
            setCenterX(newX);
          }  
          double newY = mouseEvent.getY() + dragDelta.y;
          if (newY > 0 && newY < getScene().getHeight()) {
            setCenterY(newY);
          }  
        }
      });
      setOnMouseEntered(new EventHandler<MouseEvent>() {
        @Override public void handle(MouseEvent mouseEvent) {
          if (!mouseEvent.isPrimaryButtonDown()) {
            getScene().setCursor(Cursor.HAND);
          }
        }
      });
      setOnMouseExited(new EventHandler<MouseEvent>() {
        @Override public void handle(MouseEvent mouseEvent) {
          if (!mouseEvent.isPrimaryButtonDown()) {
            getScene().setCursor(Cursor.DEFAULT);
          }
        }
      });
    }

    // records relative x and y co-ordinates.
    private class Delta { double x, y; }
  }  
}

上面的代码是基于一个圆的，所以很容易跟踪圆的 centerX 和 centerY 属性。

对于任意形状的节点，您可以使用以下代码在其父节点中跟踪其中心属性：

class Center {
    private ReadOnlyDoubleWrapper centerX = new ReadOnlyDoubleWrapper();
    private ReadOnlyDoubleWrapper centerY = new ReadOnlyDoubleWrapper();

    public Center(Node node) {
        calcCenter(node.getBoundsInParent());
        node.boundsInParentProperty().addListener(new ChangeListener<Bounds>() {
            @Override public void changed(
                   ObservableValue<? extends Bounds> observableValue, 
                   Bounds oldBounds, 
                   Bounds bounds
            ) {
                calcCenter(bounds);
            }
        });
    }

    private void calcCenter(Bounds bounds) {
        centerX.set(bounds.getMinX() + bounds.getWidth()  / 2);
        centerY.set(bounds.getMinY() + bounds.getHeight() / 2);
    }

    ReadOnlyDoubleProperty centerXProperty() {
        return centerX.getReadOnlyProperty();
    }

    ReadOnlyDoubleProperty centerYProperty() {
        return centerY.getReadOnlyProperty();
    }
}

将 Center 代码应用于上面的 Anchor 示例，您将获得以下代码：

Anchor start = new Anchor(Color.PALEGREEN, startX, startY);
Anchor end   = new Anchor(Color.TOMATO,    endX,   endY);

Center startCenter = new Center(start);
Center endCenter   = new Center(end);

Line line = new BoundLine(
        startCenter.centerXProperty(),
        startCenter.centerYProperty(),
        endCenter.centerXProperty(),
        endCenter.centerYProperty()
);

如果您想跟踪场景中的任意节点，而不仅仅是兄弟节点，您可能需要查看node.getLayoutBounds和node.getLocalToSceneTransform函数。