問題描述

我想為我的應用程序實施 DnD 以僅接受特定擴展名的文件(例如 wrl).如果文件將被接受，我想將光標更改為拖動光標，并在拖放錯誤擴展名的文件時恢復為正常光標.

I would like to implement DnD for my application to accept only files of certain extension (eg. wrl). I would like to change the cursor to a drag cursor if the file will be accepted and revert back to normal cursor when the file of wrong extension is drag and dropped.

我一直在關注 http://中的以下教程/示例docs.oracle.com/javase/tutorial/uiswing/dnd/toplevel.html

我所做的更改是在 canImport 函數中

The change that I make is in the canImport function

    public boolean canImport(TransferHandler.TransferSupport support) 
    {
        if (!support.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) 
        {
            return false;
        }

        Transferable t = support.getTransferable();

        try 
        {
          java.util.List<File> l = (java.util.List<File>)t.getTransferData(DataFlavor.javaFileListFlavor);
          if (l.size() != 1)
          {
            return false;
          }

          File f = l.get(0);

          String extension = f.getName().substring(f.getName().lastIndexOf("."));

          return extension.equalsIgnoreCase(".wrl");
        } 

        catch (UnsupportedFlavorException e) 
        {
            return false;
        } 
        catch (IOException e) 
        {
            return false;
        }
    }

當我在不同的文件中拖動時，這會正常運行.但是，當我刪除文件時，出現以下異常

This behaves correctly when I drag over in different files. However, when I drop the file, I get the following exception

Exception in thread "AWT-EventQueue-0" java.awt.dnd.InvalidDnDOperationException: No drop current
    at sun.awt.dnd.SunDropTargetContextPeer.getTransferData(SunDropTargetContextPeer.java:227)
    at sun.awt.datatransfer.TransferableProxy.getTransferData(TransferableProxy.java:56)
    at java.awt.dnd.DropTargetContext$TransferableProxy.getTransferData(DropTargetContext.java:359)
    at appl.TopLevelTransferHandlerDemo$1.canImport(TopLevelTransferHandlerDemo.java:207)
    at javax.swing.TransferHandler$DropHandler.drop(TransferHandler.java:1454)
    at java.awt.dnd.DropTarget.drop(DropTarget.java:434)
    at javax.swing.TransferHandler$SwingDropTarget.drop(TransferHandler.java:1193)
    at sun.awt.dnd.SunDropTargetContextPeer.processDropMessage(SunDropTargetContextPeer.java:519)
    at sun.awt.dnd.SunDropTargetContextPeer$EventDispatcher.dispatchDropEvent(SunDropTargetContextPeer.java:832)
    at sun.awt.dnd.SunDropTargetContextPeer$EventDispatcher.dispatchEvent(SunDropTargetContextPeer.java:756)
    at sun.awt.dnd.SunDropTargetEvent.dispatch(SunDropTargetEvent.java:30)
    at java.awt.Component.dispatchEventImpl(Component.java:4487)
    at java.awt.Container.dispatchEventImpl(Container.java:2099)
    at java.awt.Component.dispatchEvent(Component.java:4460)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
    at java.awt.LightweightDispatcher.processDropTargetEvent(Container.java:4312)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4163)
    at java.awt.Container.dispatchEventImpl(Container.java:2085)
    at java.awt.Window.dispatchEventImpl(Window.java:2478)
    at java.awt.Component.dispatchEvent(Component.java:4460)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

非常感謝任何幫助

推薦答案

我上次檢查時，這在 Mac 上不起作用，但 Java 7 可能會改變...

The last time I checked, this didn't work on Mac's, but that might have changed with Java 7...

現在，請記住，當談到拖放時，沒有簡單的答案可以解決所有問題.

Now, remember, when it comes to drag'n'drop, there is no easy answer that will do everything.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.awt.dnd.DnDConstants;
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.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.List;
import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestDragNDrop {

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

    public TestDragNDrop() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public static class TestPane extends JPanel implements DropTargetListener {

        public enum DragState {

            Waiting,
            Accept,
            Reject
        }
        private DragState state = DragState.Waiting;
        private BufferedImage happy;
        private BufferedImage wait;
        private BufferedImage sad;

        public TestPane() {
            DropTarget dt = new DropTarget(
                    this,
                    DnDConstants.ACTION_COPY_OR_MOVE,
                    this,
                    true);

            setBackground(Color.BLACK);
            try {
                happy = ImageIO.read(getClass().getResource("/Happy.png"));
                wait = ImageIO.read(getClass().getResource("/Wait.png"));
                sad = ImageIO.read(getClass().getResource("/Sad.png"));
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(300, 300);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            BufferedImage bg = null;
            switch (state) {
                case Waiting:
                    bg = wait;
                    break;
                case Accept:
                    bg = happy;
                    break;
                case Reject:
                    bg = sad;
                    break;
            }
            if (bg != null) {
                int x = (getWidth() - bg.getWidth()) / 2;
                int y = (getHeight() - bg.getHeight()) / 2;
                g.drawImage(bg, x, y, this);
            }
        }

        @Override
        public void dragEnter(DropTargetDragEvent dtde) {
            state = DragState.Reject;
            Transferable t = dtde.getTransferable();
            if (t.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
                try {
                    Object td = t.getTransferData(DataFlavor.javaFileListFlavor);
                    if (td instanceof List) {
                        state = DragState.Accept;
                        for (Object value : ((List) td)) {
                            if (value instanceof File) {
                                File file = (File) value;
                                String name = file.getName().toLowerCase();
                                if (!name.endsWith(".png")) {
                                    state = DragState.Reject;
                                    break;
                                }
                            }
                        }
                    }
                } catch (UnsupportedFlavorException | IOException ex) {
                    ex.printStackTrace();
                }
            }
            if (state == DragState.Accept) {
                dtde.acceptDrag(DnDConstants.ACTION_COPY);
            } else {
                dtde.rejectDrag();
            }
            repaint();
        }

        @Override
        public void dragOver(DropTargetDragEvent dtde) {
        }

        @Override
        public void dropActionChanged(DropTargetDragEvent dtde) {
        }

        @Override
        public void dragExit(DropTargetEvent dte) {
            state = DragState.Waiting;
            repaint();
        }

        @Override
        public void drop(DropTargetDropEvent dtde) {
            state = DragState.Waiting;
            repaint();
        }
    }
}

這篇關于JFrame 上特定擴展名的 Java Drag-n-Drop 文件的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！