Java中的Drag and Drop详解与代码示例

技术2022-05-11 112

我最近对对Java中的Drag and Drop做了一个总结, 觉得大致可以通过两种方法实现Drag and Drop: 1.比较初级的D&D:只利用java.awt.datatransfer.*中的类实现. 2.高级D&D: 利用javax.awt.dnd.*中的类实现.

比较初级D&D:只利用java.awt.datatransfer.*中的类实现. 这种方法只支持对JComponent的拖拽. Drag and Drop的问题简单的说要涉及到两个部分: Drag Source, Drop target和Transferable 即从哪里drag来的, 以及drop到哪里去, 以及传输的数据. Drag Source可以分为两种: 1.第一种是这样的JComponent, 他们有dragEnabled属性.这些JComponent包括: javax.swing.JColorChooser javax.swing.JFileChooser javax.swing.JList javax.swing.JTable javax.swing.JTree javax.swing.text.JTextComponent 这些JComponent要想作为一个Drag Source只要调用setDragEnabled( true)即可, 不用多余的操作. 2. 另一种Drag Source没有dragEnabled属性, 也就没有setDragEnabled方法, 要想作为Drag Source, 那就要给Component添加MouseMotionListener, 并实现mouseDragged方法, 后面会举例介绍. Drop Target, 任何JComponent都可以作为Drop Target, 但是也只有JComponent以及它的子类可以作为Drop Target, 其它的不行. Transferable 所有的Transferable都是javax.swing.Transferable的子类, 但是细分还是可以分为两种情况: 第一种是利用javax.swing.Transferable, 因为javax.swing.Transferable 是一个具体类我们可以直接调用new TransferHandler( String property )生成的transfer handler 作为Component的Transfer Handler, 这样的transfer handler可以将 Java Bean 属性从一个组件传输到另一个组件的传输处理程序。第二种则是自定义一个TransferHandler的子类, 你可以在这个类中实现复杂的拖拽操作.下面有两个例子.第一个例子用简单的javax.swing.Transferable, 第二个例子定义一个javax.swing.Transferable的子类.例一

import java.awt. * ; import java.awt.event. * ; import javax.swing. * ; import javax.swing.event. * ; public class LabelDnd { private JFrame mainFrame; private JPanel mainPanel; private JLabel label; private JTextField textField; private JColorChooser colorChooser; private JMenuBar menuBar = new JMenuBar(); private JMenu menu = new JMenu( "Menu" ); private JMenuItem menuItem = new JMenuItem( "Handle Foregound" ); private TransferHandler t1 = new TransferHandler( "text" ) ; private TransferHandler t2 = new TransferHandler( "foreground" ); public LabelDnd() { mainFrame = new JFrame(); mainPanel = new JPanel( new BorderLayout() ); label = new JLabel( "label" ); label.setTransferHandler( t1 ); menuItem.addActionListener( new ActionListener() { public void actionPerformed( ActionEvent e ) { if( label.getTransferHandler().equals( t1 ) ) { LabelDnd.this.menuItem.setText( "Handle Text" ); label.setTransferHandler( t2 ); } else { LabelDnd.this.menuItem.setText( "Handle Foreground" ); label.setTransferHandler( t1 ); } } }); menu.add( menuItem ); menu.setTransferHandler( t1 ); menuBar.add( menu ); mainFrame.setJMenuBar( menuBar ); label.addMouseListener( new MouseAdapter() { public void mousePressed( MouseEvent e ) { JComponent c = (JComponent)e.getSource(); TransferHandler handler = c.getTransferHandler(); handler.exportAsDrag( c, e, TransferHandler.COPY ); } }); textField = new JTextField( 20 ); textField.setDragEnabled( true ); colorChooser = new JColorChooser(); colorChooser.setDragEnabled( true ); mainPanel.add( label, BorderLayout.PAGE_START ); mainPanel.add( textField, BorderLayout.PAGE_END ); mainPanel.add( colorChooser, BorderLayout.WEST ); mainFrame.getContentPane().add( mainPanel ); mainFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); mainFrame.pack(); mainFrame.setLocationRelativeTo( null ); mainFrame.setVisible( true ); } public static void main( String[] args ) { new LabelDnd(); }}

效果如下:

你可以试着拖拽下。

例二PictureDnd.java

package dt; import java.awt. * ; import javax.swing. * ; import java.awt.event. * ; import javax.swing.event. * ; import demo.gui.PictureComponent; import java.awt.datatransfer. * ; import java.io. * ; public class PictureDnd { JFrame mainFrame; JPanel mainPanel; PictureComponent[] pictures; public static void main( String[] args ) { new PictureDnd(); } public PictureDnd() { mainFrame = new JFrame(); mainPanel = new JPanel( new GridLayout( 2, 2 ) ); pictures = new PictureComponent[ 4 ]; pictures[ 0 ] = new PictureComponent( new ImageIcon( "Sunset.jpg" ).getImage() ); pictures[ 1 ] = new PictureComponent( new ImageIcon( "Winter.jpg" ).getImage() ); pictures[ 2 ] = new PictureComponent( null ); pictures[ 3 ] = new PictureComponent( null ); mainPanel.add( pictures[ 0 ] ); mainPanel.add( pictures[ 1 ] ); mainPanel.add( pictures[ 2 ] ); mainPanel.add( pictures[ 3 ] ); mainPanel.setBorder( BorderFactory.createEmptyBorder( 20, 20, 20, 20 ) ); mainFrame.getContentPane().add( mainPanel ); mainFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); mainFrame.setSize( 350, 400 ); mainFrame.setLocationRelativeTo( null ); mainFrame.setVisible( true ); }}

PicrureComponent.java

package demo.gui; import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Image; import java.awt.event.FocusEvent; import java.awt.event.FocusListener; import java.awt.event.MouseEvent; import java.awt.event.MouseListener; import java.util.HashSet; import javax.swing.JComponent; public class PictureComponent extends JComponent implements FocusListener, MouseListener { Image image; HashSet< PictureComponent > pcs = new HashSet< PictureComponent >(); public PictureComponent( Image image ) { this.image = image; setPreferredSize( new Dimension(125, 125 ) ); setFocusable( true ); setTransferHandler( new PictureTransferHandler() ); addFocusListener( this ); addMouseListener( this ); } public HashSet< PictureComponent > getPcs() { return this.pcs; } public void setPcs( HashSet< PictureComponent > pcs ) { this.pcs = pcs; } public Image getImage() { return this.image; } public void setImage( Image image ){ this.image = image; repaint(); } public void paintComponent( Graphics graphics ){ Graphics g = graphics.create(); g.setColor( Color.white ); g.fillRect( 0, 0, 125,125 ); if( image != null ) { g.drawImage( image, 0, 0, 125, 125, Color.BLACK, this ); } if( isFocusOwner() ) { g.setColor( Color.red ); } else { g.setColor( Color.black ); } g.drawRect( 0, 0, 125, 125 ); g.dispose(); } public void focusGained( FocusEvent e ) { repaint(); } public void focusLost( FocusEvent e ) { repaint(); } public void mouseClicked( MouseEvent e ) { requestFocusInWindow(); } public void mouseEntered( MouseEvent e ) {} public void mousePressed( MouseEvent e ) {} public void mouseExited( MouseEvent e ) {} public void mouseReleased( MouseEvent e ) {}}

TransferablePicture:

package demo.gui; import java.awt.Image; import java.awt.datatransfer.DataFlavor; import java.awt.datatransfer.Transferable; /* Transferalbe */ public class TransferablePicture implements Transferable { DataFlavor[] flavors = { DataFlavor.imageFlavor }; Image image; public TransferablePicture( Image image ) { this.image = image; } public DataFlavor[] getTransferDataFlavors() { return flavors; } public Object getTransferData( DataFlavor flavor ) { if( flavor.equals( DataFlavor.imageFlavor ) ) { return image; } return null; } public boolean isDataFlavorSupported( DataFlavor flavor ) { return flavor.equals( DataFlavor.imageFlavor ); }}

PictureTransferHandler.java

package demo.gui; import java.awt.Image; import java.awt.datatransfer.DataFlavor; import java.awt.datatransfer.Transferable; import java.awt.datatransfer.UnsupportedFlavorException; import java.io.IOException; import javax.swing.Icon; import javax.swing.ImageIcon; import javax.swing.JComponent; import javax.swing.TransferHandler; import dt.TransferablePicture; /* Transfer Handler */ class PictureTransferHandler extends TransferHandler { public Transferable createTransferable( JComponent c ) { PictureComponent pc = (PictureComponent)c; return new TransferablePicture( pc.getImage() ); } public boolean canImport( JComponent c, DataFlavor[] flavors ) { for( DataFlavor flavor : flavors ) { if( flavor.equals( DataFlavor.imageFlavor ) ) { return true; } } return false; } public boolean importData( JComponent c, Transferable t ) { if( canImport(c, t.getTransferDataFlavors() ) ) { PictureComponent pc = ( PictureComponent )c; try { Image image = (Image)t.getTransferData( DataFlavor.imageFlavor ); pc.setImage( image ); System.out.println( "它能接受" ); return true; } catch( UnsupportedFlavorException e ) { e.printStackTrace(); } catch( IOException e ) { e.printStackTrace(); } } System.out.println( "它不能接受" ); return false; } public void exportDone( JComponent c, Transferable data, int action ) { PictureComponent picture = ( PictureComponent )c; if( action == MOVE ) { picture.setImage( null ); } } public int getSourceActions( JComponent c ){ return COPY_OR_MOVE; } public Icon getVisualRepresentation( Transferable t ) { Image image = null; try { System.out.println( "getVisualRepresentation" ); image = (Image)t.getTransferData( DataFlavor.imageFlavor ); } catch( Exception e ) { e.printStackTrace(); } return new ImageIcon( image ); }}

效果如下:

2.高级D&D:利用javax.awt.dnd.*中的类实现. 第二种实现方法和第一种的区别主要是在Drag Source和Drop Target上.而且这第二种实现方法支持所有Component及其子类上实现拖拽,而不止是JComponent. Drag Target 一个对象那个如果想作为拖拽源的话，必须和五个对象建立联系，这五个对象分别是： * java.awt.dnd.DragSource 获取DragSource的方法很简单，直接调用DragSource.getDefaultDragSource()；就可以得到DragSource对象 * java.awt.dnd.DragGestureRecognizer DragGestureRecognizer类中实现了一些与平台无关的方法，我们如果想在自己的组件上实现拖拽的话只要调用createDefaultDragGestureRecognizer()方法就可以了该方法接收三个参数，建立组件和拖拽动作之间的关系 * java.awt.dnd.DragGestureListener 当建立了组件和拖拽动作之间的联系后，如果用户执行了拖拽操作，组件将发送一个消息给DragGestureListener监听器 DragGestureListener监听器接下来会发送一个startDrag()消息给拖拽源对象，告诉组件应该执行拖拽的初始化操作了拖拽源会产生一个DragSourceContext对象来监听动作的状态，这个监听过程是通过监听本地方法DragSourceContextPeer来实现的 * java.awt.datatransfer.Transferable * java.awt.dnd.DragSourceListener DragSourceListener接口负责当鼠标拖拽对象经过组件时的可视化处理， DragSourceListener接口的显示结果只是暂时改变组件的外观同时他提供一个feedback，当用户的拖拽操作完成之后会收到一个dragDropEnd的消息，我们可以在这个函数中执行相应的操作再来回顾一下拖拽源的建立过程 1.DragGestureRecognizer 确认一个拖拽操作，同时告知 DragGestureListener. 2.假如actions and/or flavors are OK, DragGestureListener 让 DragSource 调用 startDrag(). 3.DragSource建立一个 DragSourceContext和一个DragSourceContextPeer. 4.DragSourceContext 把它自己作为一个DragSourceListener,侦听DragSourceContextPeer.DragSourceContextPeer会从本地系统得到Coponent的状态改变的通知(component entered/exited/is over), 并把他们代理给DragSourceContext.5.DragSourceContext通知 DragSourceListener,而DragSourceListener提供 drag over 的反馈(如果DropTargetListener接受这个动作). 典型的反馈包括让DrogSourceContext改变鼠标. 6.一旦drop完毕, DragSourceListener就得到一个dragDropEnd的通知消息. Drop Source 创建一个 droppable Component必须和下面两个对象发生关联 * java.awt.dnd.DropTarget DropTarget构造函数使DropTarget 和 DropTargetListener objects发生关联 Droptarget对象提供 setComponent 和addDropTargetListener 两个方法 * java.awt.dnd.DropTargetListener DropTargetListener需要与一个Component联系, 以让DropTargetListener在Component操作的时候能够显示”drag under”效果. 下面的这个例子以第二种方式实现拖拽:DragAndDrop.java

package dnd; import java.awt. * ; import javax.swing. * ; import java.awt.dnd. * ; import java.awt.datatransfer. * ; import java.io. * ; import javax.swing.tree. * ; public class DragAndDrop extends JFrame { JScrollPane jScrollPane1 = new JScrollPane(); JTextArea jTextArea1 = new JTextArea(); public DragAndDrop() { this.getContentPane().setLayout( new BorderLayout() ); jScrollPane1.getViewport().setBackground( new Color( 105, 38, 125 ) ); jTextArea1.setBackground( Color.orange ); jTextArea1.setToolTipText( "" ); JTree jtr = new JTree(); jtr.setBackground( Color.BLUE ); jScrollPane1.getViewport().add( jtr ); this.getContentPane().add( jTextArea1, BorderLayout.PAGE_END ); this.getContentPane().add( jScrollPane1, BorderLayout.PAGE_START ); // Drag And Drop Relative. DragSource dragSource = DragSource.getDefaultDragSource(); dragSource.createDefaultDragGestureRecognizer( jtr, DnDConstants.ACTION_COPY_OR_MOVE, new DragAndDropDragGestureListener() ); DropTarget dropTarget = new DropTarget( jTextArea1, new DragAndDropDropTargetListener() ); } public static void main( String[] args ) { DragAndDrop dad = new DragAndDrop(); dad.setTitle( "拖拽演示" ); dad.setSize( 400, 300 ); dad.setVisible( true ); }}

DragAndDropDragGestureListener.java

package dnd; import java.awt.dnd.DragGestureEvent; import java.awt.dnd.DragGestureListener; import java.awt.dnd.DragSource; import javax.swing.JTree; import javax.swing.tree.DefaultMutableTreeNode; import javax.swing.tree.TreePath; /* Drag Gesture Listener */ public class DragAndDropDragGestureListener implements DragGestureListener { public void dragGestureRecognized( DragGestureEvent dge ) { JTree tree = (JTree)dge.getComponent(); TreePath path = tree.getSelectionPath(); if( path != null ) { DefaultMutableTreeNode selection = ( DefaultMutableTreeNode )path.getLastPathComponent(); DragAndDropTransferable dragAndDropTransferable = new DragAndDropTransferable( selection ); dge.startDrag( DragSource.DefaultCopyDrop, dragAndDropTransferable, new DragAndDropDragSourceListener() ); } }}

DragAndDropDragSourceListener.java

package dnd; import java.awt.dnd.DnDConstants; import java.awt.dnd.DragSource; import java.awt.dnd.DragSourceContext; import java.awt.dnd.DragSourceDragEvent; import java.awt.dnd.DragSourceDropEvent; import java.awt.dnd.DragSourceEvent; import java.awt.dnd.DragSourceListener; import javax.swing.JTree; import javax.swing.tree.DefaultMutableTreeNode; import javax.swing.tree.TreePath; /* Drag Source Listener */ public class DragAndDropDragSourceListener implements DragSourceListener { public void dragDropEnd( DragSourceDropEvent e ) { if( e.getDropSuccess() ) { int dropAction = e.getDropAction(); if( dropAction == DnDConstants.ACTION_MOVE ) { //System.out.println( "MOVE: remove node" ); } } } public void dragEnter( DragSourceDragEvent e ) { DragSourceContext context = e.getDragSourceContext(); int dropAction = e.getDropAction(); if( ( dropAction & DnDConstants.ACTION_COPY ) != 0 ) { context.setCursor( DragSource.DefaultCopyDrop ); } else if( ( dropAction & DnDConstants.ACTION_MOVE ) != 0 ) { context.setCursor( DragSource.DefaultMoveDrop ); } else { context.setCursor( DragSource.DefaultCopyNoDrop ); } } public void dragExit( DragSourceEvent e ) {} public void dragOver( DragSourceDragEvent e ){} public void dropActionChanged( DragSourceDragEvent e ){}}

DragAndDropDropTargetListener.java

package dnd; import java.awt.datatransfer.DataFlavor; import java.awt.datatransfer.Transferable; import java.awt.datatransfer.UnsupportedFlavorException; import java.awt.dnd.DropTarget; import java.awt.dnd.DropTargetDragEvent; import java.awt.dnd.DropTargetDropEvent; import java.awt.dnd.DropTargetEvent; import java.awt.dnd.DropTargetListener; import java.io.IOException; import javax.swing.JTextArea; /* Drop Target Listener */ public class DragAndDropDropTargetListener implements DropTargetListener { public void dragEnter( DropTargetDragEvent e ) {} public void dragOver( DropTargetDragEvent e ) {} public void dropActionChanged( DropTargetDragEvent e ) {} public void dragExit( DropTargetEvent e ) {} public void drop( DropTargetDropEvent e ) { Transferable t = e.getTransferable(); String s = ""; try { if( t.isDataFlavorSupported( DataFlavor.stringFlavor ) ) { s = t.getTransferData( DataFlavor.stringFlavor ).toString(); } } catch( IOException ioe ) { ioe.printStackTrace(); } catch( UnsupportedFlavorException ufe ) { ufe.printStackTrace(); } System.out.println( s ); DropTarget dt = (DropTarget)e.getSource(); JTextArea d = ( JTextArea )dt.getComponent(); if( s != null && s.equals( "" ) == false ) { d.append( s + " "); } }}

DragAndDropTransferable.java

package dnd; import java.awt.datatransfer.DataFlavor; import java.awt.datatransfer.Transferable; import java.awt.datatransfer.UnsupportedFlavorException; import java.io.IOException; import javax.swing.tree.DefaultMutableTreeNode; /* Drop Transferable */ public class DragAndDropTransferable implements Transferable { private DefaultMutableTreeNode treeNode; public DragAndDropTransferable( DefaultMutableTreeNode treeNode ) { this.treeNode = treeNode; } DataFlavor[] flavors = { DataFlavor.stringFlavor }; public DataFlavor[] getTransferDataFlavors() { return flavors; } public boolean isDataFlavorSupported( DataFlavor flavor ) { for( DataFlavor df : flavors ) { if( df.equals( flavor ) ) { return true; } } return false; } public Object getTransferData( DataFlavor df ) throws UnsupportedFlavorException, IOException { return treeNode; }}

效果如下:

参考网页:http://blog.csdn.net/XXKKFF/archive/2007/01/11/1480506.aspxhttp://showmealone.blog.sohu.com/8609852.html3. Drag and Drop Specifications: http://java.sun.com/j2se/1.5/pdf/dnd1.pdf

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