Java拖放JFrame上特定扩展名的文件 [英] Java Drag-n-Drop files of specific extension on JFrame
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问题描述
我想为我的应用程序实现DnD，只接受某些扩展名的文件（例如wrl）。如果文件被接受，我想将光标更改为拖动光标，当拖放错误扩展名的文件时，将其恢复为普通光标。
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.
I以下教程/示例来自 http://docs.oracle。 com / javase / tutorial / uiswing / dnd / toplevel.html
I have been following the following tutorial/example from http://docs.oracle.com/javase/tutorial/uiswing/dnd/toplevel.html
我所做的更改是在canImport函数中
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;
}
}
当我在不同的文件中拖动时，这个行为正确。但是，当我删除文件时，我得到以下例外：
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)
任何帮助非常感谢
推荐答案
最后一次我检查，这在Mac上没有工作，但是可能已经改变了Java 7 ...
The last time I checked, this didn't work on Mac's, but that might have changed with Java 7...
现在，请记住，当拖曳拖放时，没有任何简单的答案可以做所有事情。
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();
}
}
}
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