以前创建的元素在创建新元素时的娱乐SWT Draw2d

Question

我已经编写了允许拖放到画布上的代码。在“放下”时，画布上将绘制一个RectangleFigure。问题是，当我第二次放置在画布上时，屏幕上会创建第一个放置元素的另一个副本。同样，第三次，前两个元素被重新创建（我们知道这是真实的，因为如果从原始位置拖动其中一个元素，您可以看到它下面的重新创建的元素）有人可以告诉我如何防止这种娱乐发生？ *我已加入的短片可测试的代码说明

import org.eclipse.draw2d.ColorConstants; 
import org.eclipse.draw2d.Figure; 
import org.eclipse.draw2d.IFigure; 
import org.eclipse.draw2d.LightweightSystem; 
import org.eclipse.draw2d.MouseEvent; 
import org.eclipse.draw2d.MouseListener; 
import org.eclipse.draw2d.MouseMotionListener; 
import org.eclipse.draw2d.RectangleFigure; 
import org.eclipse.draw2d.geometry.Dimension; 
import org.eclipse.draw2d.geometry.Point; 
import org.eclipse.draw2d.geometry.Rectangle; 
import org.eclipse.swt.SWT; 


import org.eclipse.swt.dnd.DND; 
import org.eclipse.swt.dnd.DragSource; 
import org.eclipse.swt.dnd.DragSourceEvent; 
import org.eclipse.swt.dnd.DragSourceListener; 
import org.eclipse.swt.dnd.DropTarget; 
import org.eclipse.swt.dnd.DropTargetEvent; 
import org.eclipse.swt.dnd.DropTargetListener; 
import org.eclipse.swt.dnd.TextTransfer; 
import org.eclipse.swt.dnd.Transfer; 
import org.eclipse.swt.events.PaintEvent; 
import org.eclipse.swt.events.PaintListener; 
import org.eclipse.swt.graphics.GC; 
import org.eclipse.swt.widgets.Display; 
import org.eclipse.swt.widgets.Shell; 
import org.eclipse.swt.widgets.Menu; 
import org.eclipse.swt.widgets.Group; 
import org.eclipse.swt.widgets.Canvas; 
import org.eclipse.wb.swt.SWTResourceManager; 
import org.eclipse.swt.widgets.Label; 

/** 
* 
*Shortest complete testable code demonstrating the repeated creation problem 
*/ 
public class RepeatDrop 
{ 
/** 
* Launch the application. 
* 
* @param args 
*/ 

private Shell shell; 
private Display display; 
private Menu menu; 
private Group grpPalette; 
private final Label lblUnicorn; 
private Group grpCanvas; 
private final Canvas canvas; 

public static void main(String args[]) { 
    new RepeatDrop(); 
} 

/** 
* Create the shell. 
* 
* @param display 
*/ 
public RepeatDrop() { 
    display = new Display(); 
    shell = new Shell(display); 
    shell.setText("SWT Application"); 
    shell.setSize(450, 393); 

    Group grpPalette = new Group(shell, SWT.NONE); 
    grpPalette.setText("Palette"); 
    grpPalette.setBounds(0, 0, 88, 325); 

    lblUnicorn = new Label(grpPalette, SWT.BORDER | SWT.HORIZONTAL 
      | SWT.CENTER); 
    lblUnicorn.setText("UNICORN"); 
    // ADDED A FINAL HERE!! 
    lblUnicorn.setAlignment(SWT.CENTER); 
    lblUnicorn.setBounds(10, 24, 68, 53); 

    final Group grpCanvas = new Group(shell, SWT.NONE); 
    grpCanvas.setText("Canvas"); 
    grpCanvas.setBounds(94, 0, 330, 325); 

    canvas = new Canvas(grpCanvas, SWT.NONE); 
    canvas.setBackground(SWTResourceManager.getColor(253, 245, 230)); 
    canvas.setBounds(10, 20, 320, 295); 


    LightweightSystem lws = new LightweightSystem(canvas); // 
    final IFigure panel = new Figure(); // 
    lws.setContents(panel); // 

    DragSource dragSource1 = new DragSource(lblUnicorn, DND.DROP_COPY); 
    Transfer[] transfers1 = new Transfer[] { TextTransfer.getInstance() }; 
    dragSource1.setTransfer(transfers1); 
    dragSource1.addDragListener(new DragSourceListener() { 
     public void dragStart(DragSourceEvent event) { 
      if (lblUnicorn.getText().length() == 0) { 
       event.doit = false; 
      } 
     } 

     public void dragSetData(DragSourceEvent event) { 
      if (TextTransfer.getInstance().isSupportedType (event.dataType)) { 
       event.data = lblUnicorn.getText(); 
      } 
     } 

     public void dragFinished(DragSourceEvent event) { 
     } 
     }); 

    Transfer[] types = new Transfer[] { TextTransfer.getInstance() }; 
    DropTarget dropTarget = new DropTarget(canvas, DND.DROP_COPY 
      | DND.DROP_DEFAULT); 
    dropTarget.setTransfer(types); 



    dropTarget.addDropListener(new DropTargetListener() { 
     public void dragEnter(DropTargetEvent event) { 
      if (event.detail == DND.DROP_DEFAULT) { 
       if ((event.operations & DND.DROP_COPY) != 0) { 
        event.detail = DND.DROP_COPY; 
       } else { 
        event.detail = DND.DROP_NONE; 
       } 
      } 
     } 

     public void dragLeave(DropTargetEvent event) { 
     } 

     public void dragOperationChanged(DropTargetEvent event) { 
     } 

     public void dragOver(DropTargetEvent event) { 
     } 



     public void drop(DropTargetEvent event) { 
     } 


     public void dropAccept(final DropTargetEvent event) 
     { 

      if (TextTransfer.getInstance().isSupportedType(
        event.currentDataType)) { 
       String d = (String) TextTransfer.getInstance() 
         .nativeToJava(event.currentDataType); 

       final String finald= d; 

       GC gc = new GC(canvas); 
       canvas.redraw(); 




       canvas.addPaintListener(new PaintListener() { 
        public void paintControl(PaintEvent e) { 


org.eclipse.swt.graphics.Point droppoint = canvas.toControl(event.x, event.y); 

         //DRAW 2D SECTION 
         RectangleFigure node1 = new RectangleFigure(); 
         Rectangle rect=new Rectangle(droppoint.x, droppoint.y, 20, 20); 
         Rectangle rect2=new Rectangle(droppoint.x, droppoint.y, 100, 25); 
         node1.setBounds(rect); 
         node1.setBackgroundColor(ColorConstants.cyan); 


         org.eclipse.draw2d.Label droppedName= 
           new org.eclipse.draw2d.Label(finald); 
         droppedName.setLocation(new Point(droppoint.x, droppoint.y)); //draw2d. point 
         droppedName.setBounds(rect2); 

         node1.add(droppedName); 
         panel.add(node1); 
         panel.add(droppedName); 

         Dragger fig = new Dragger(node1); 
         Dragger caption = new Dragger(droppedName); 
         //DRAW 2D SECTION 

        } 

       }); 
      } 
     } 
    }); 


    shell.pack(); 
    shell.open(); 

    while (!shell.isDisposed()) { 
     if (!display.readAndDispatch()) { 
      display.sleep(); 
     } 
    } 

} 

static class Dragger extends MouseMotionListener.Stub implements MouseListener 
{ 

     public Dragger(IFigure figure){ 
      figure.addMouseMotionListener(this); 
      figure.addMouseListener(this); 
     } 

     Point last; 
     public void mouseReleased(MouseEvent e){ 
     } 
     public void mouseClicked(MouseEvent e){ 
     } 
     public void mouseDoubleClicked(MouseEvent e){ 
     } 
     public void mousePressed(MouseEvent e){ 
      last = e.getLocation(); 
     } 

     public void mouseDragged(MouseEvent e){ 
      Point p = e.getLocation(); 
      Dimension delta = p.getDifference(last); 
      { 
       last = p; 
       Figure f = ((Figure)e.getSource()); 
       f.setBounds(f.getBounds().getTranslated(delta.width, delta.height)); 
      } 
     } 
} 


} 

Answer 1

你的问题是由您添加每次添加一个新的身影时新PaintListener的事实导致的问题。这没有必要。实际上，您根本不需要添加任何PaintListener。 LightweightSystem将为您照顾。

这里是你的代码现在工作正常：

public class RepeatDrop 
{ 
    private Shell  shell; 
    private Display  display; 
    private final Label lblUnicorn; 
    private final Canvas canvas; 

    public static void main(String args[]) 
    { 
     new RepeatDrop(); 
    } 

    public RepeatDrop() 
    { 
     display = new Display(); 
     shell = new Shell(display); 
     shell.setText("SWT Application"); 
     shell.setLayout(new GridLayout(2, false)); 

     Group grpPalette = new Group(shell, SWT.NONE); 
     grpPalette.setText("Palette"); 
     grpPalette.setLayout(new GridLayout()); 
     grpPalette.setLayoutData(new GridData(SWT.BEGINNING, SWT.FILL, false, true)); 

     lblUnicorn = new Label(grpPalette, SWT.BORDER | SWT.HORIZONTAL | SWT.CENTER); 
     lblUnicorn.setText("UNICORN"); 
     // ADDED A FINAL HERE!! 
     lblUnicorn.setAlignment(SWT.CENTER); 

     final Group grpCanvas = new Group(shell, SWT.NONE); 
     grpCanvas.setText("Canvas"); 
     grpCanvas.setLayout(new GridLayout()); 
     grpCanvas.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true)); 

     canvas = new Canvas(grpCanvas, SWT.NONE); 
     canvas.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true)); 

     LightweightSystem lws = new LightweightSystem(canvas); // 
     final IFigure panel = new Figure(); // 
     lws.setContents(panel); // 

     DragSource dragSource1 = new DragSource(lblUnicorn, DND.DROP_COPY); 
     Transfer[] transfers1 = new Transfer[] { TextTransfer.getInstance() }; 
     dragSource1.setTransfer(transfers1); 
     dragSource1.addDragListener(new DragSourceListener() 
     { 
      public void dragStart(DragSourceEvent event) 
      { 
       if (lblUnicorn.getText().length() == 0) 
       { 
        event.doit = false; 
       } 
      } 

      public void dragSetData(DragSourceEvent event) 
      { 
       if (TextTransfer.getInstance().isSupportedType(event.dataType)) 
       { 
        event.data = lblUnicorn.getText(); 
       } 
      } 

      public void dragFinished(DragSourceEvent event) 
      { 
      } 
     }); 

     Transfer[] types = new Transfer[] { TextTransfer.getInstance() }; 
     DropTarget dropTarget = new DropTarget(canvas, DND.DROP_COPY | DND.DROP_DEFAULT); 
     dropTarget.setTransfer(types); 

     dropTarget.addDropListener(new DropTargetListener() 
     { 
      public void dragEnter(DropTargetEvent event) 
      { 
       if (event.detail == DND.DROP_DEFAULT) 
       { 
        if ((event.operations & DND.DROP_COPY) != 0) 
        { 
         event.detail = DND.DROP_COPY; 
        } 
        else 
        { 
         event.detail = DND.DROP_NONE; 
        } 
       } 
      } 

      public void dragLeave(DropTargetEvent event) 
      { 
      } 

      public void dragOperationChanged(DropTargetEvent event) 
      { 
      } 

      public void dragOver(DropTargetEvent event) 
      { 
      } 

      public void drop(DropTargetEvent event) 
      { 
      } 

      public void dropAccept(final DropTargetEvent event) 
      { 

       if (TextTransfer.getInstance().isSupportedType(event.currentDataType)) 
       { 
        String d = (String) TextTransfer.getInstance().nativeToJava(event.currentDataType); 

        org.eclipse.swt.graphics.Point droppoint = canvas.toControl(event.x, event.y); 

        // DRAW 2D SECTION 
        RectangleFigure node1 = new RectangleFigure(); 
        Rectangle rect = new Rectangle(droppoint.x, droppoint.y, 20, 20); 
        Rectangle rect2 = new Rectangle(droppoint.x, droppoint.y, 100, 25); 
        node1.setBounds(rect); 
        node1.setBackgroundColor(ColorConstants.cyan); 

        org.eclipse.draw2d.Label droppedName = new org.eclipse.draw2d.Label(d); 
        droppedName.setLocation(new Point(droppoint.x, droppoint.y)); // draw2d. 
                        // point 
        droppedName.setBounds(rect2); 

        node1.add(droppedName); 
        panel.add(node1); 
        panel.add(droppedName); 

        new Dragger(node1); 
        new Dragger(droppedName); 

        canvas.redraw(); 
       } 
      } 
     }); 

     shell.pack(); 
     shell.setSize(400, 300); 
     shell.open(); 

     while (!shell.isDisposed()) 
     { 
      if (!display.readAndDispatch()) 
      { 
       display.sleep(); 
      } 
     } 
    } 

    static class Dragger extends MouseMotionListener.Stub implements MouseListener 
    { 
     public Dragger(IFigure figure) 
     { 
      figure.addMouseMotionListener(this); 
      figure.addMouseListener(this); 
     } 

     Point last; 

     public void mouseReleased(MouseEvent e) 
     { 
     } 

     public void mouseClicked(MouseEvent e) 
     { 
     } 

     public void mouseDoubleClicked(MouseEvent e) 
     { 
     } 

     public void mousePressed(MouseEvent e) 
     { 
      last = e.getLocation(); 
     } 

     public void mouseDragged(MouseEvent e) 
     { 
      Point p = e.getLocation(); 
      Dimension delta = p.getDifference(last); 
      { 
       last = p; 
       Figure f = ((Figure) e.getSource()); 
       f.setBounds(f.getBounds().getTranslated(delta.width, delta.height)); 
      } 
     } 
    } 
} 

---

请看看我用Layout S上的方式。它更可靠，并且可以在不同的窗口大小和屏幕分辨率下更好地工作。

请同时阅读：Understanding Layouts in SWT