使用swt实现两个树之间节点上点击绘制连线

以下是使用 Eclipse SWT 实现在两个树之间绘制连线的示例代码：

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.graphics.Color;
import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Tree;
import org.eclipse.swt.widgets.TreeItem;

public class TreeLinkExample {

    private static TreeItem sourceItem = null;
    private static TreeItem targetItem = null;

    public static void main(String[] args) {
        Display display = new Display();
        Shell shell = new Shell(display);
        shell.setLayout(new FillLayout());

        Tree tree1 = new Tree(shell, SWT.BORDER);
        for (int i = 0; i < 5; i++) {
            TreeItem item = new TreeItem(tree1, SWT.NONE);
            item.setText("Item " + i);
        }

        Tree tree2 = new Tree(shell, SWT.BORDER);
        for (int i = 0; i < 5; i++) {
            TreeItem item = new TreeItem(tree2, SWT.NONE);
            item.setText("Item " + i);
        }

        Canvas canvas = new Canvas(shell, SWT.NONE);
        canvas.addPaintListener(new PaintListener() {

            @Override
            public void paintControl(PaintEvent e) {
                if (sourceItem != null && targetItem != null) {
                    GC gc = e.gc;
                    Rectangle sourceBounds = sourceItem.getBounds();
                    Rectangle targetBounds = targetItem.getBounds();
                    Point sourceCenter = new Point(sourceBounds.x + sourceBounds.width / 2,
                            sourceBounds.y + sourceBounds.height / 2);
                    Point targetCenter = new Point(targetBounds.x + targetBounds.width / 2,
                            targetBounds.y + targetBounds.height / 2);
                    gc.setLineWidth(2);
                    gc.setForeground(new Color(e.display, 0, 0, 255));
                    gc.drawLine(sourceCenter.x, sourceCenter.y, targetCenter.x, targetCenter.y);
                }
            }
        });

        tree1.addListener(SWT.Selection, event -> {
            sourceItem = (TreeItem) event.item;
            redrawCanvas(canvas);
        });

        tree2.addListener(SWT.Selection, event -> {
            targetItem = (TreeItem) event.item;
            redrawCanvas(canvas);
        });

        shell.setSize(400, 300);
        shell.open();
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch()) {
                display.sleep();
            }
        }
        display.dispose();
    }

    private static void redrawCanvas(Canvas canvas) {
        canvas.redraw();
        canvas.update();
    }
}

这个示例程序创建了两个树控件和一个 `Canvas` 控件，并在树控件上添加了 `Selection` 监听器，在监听器中记录了选中的项。同时，在 `Canvas` 上添加了 `PaintListener`，在监听器中根据选中的两个树项绘制了一条连接线。当有树项被选中时，先记录下来，然后调用 `redrawCanvas` 方法重绘 `Canvas` 控件。