我正在研究 JList 组件的拖放支持,并且我希望能够支持从文件浏览器拖入的文件。然而,我只想允许拖入文件而不是文件夹。因此我尝试在我的 TransferHandler 中检查它,如下所示:
@Override
public boolean canImport(TransferSupport support) {
if (support.getComponent().equals(this.resourceFileList)) {
if (!support.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
return false;
} else {
try {
// get file list
Transferable transferable = support.getTransferable();
Object transferData = transferable.getTransferData(DataFlavor.javaFileListFlavor);
// check for folders
boolean containsFiles = false;
List files = (List) transferData;
for (int i = 0; i < files.size(); i++) {
File file = (File) files.get(i);
if (!file.isDirectory()) {
containsFiles = true;
}
}
// return file indicator
return containsFiles;
} catch (IOException | UnsupportedFlavorException e) {
System.out.println("Unable to check for folders due to the following exception:\n" + e);
return false;
}
}
} else {
return false;
}
}
不幸的是transferData在这里似乎为空。然而,这并不是在调用 TransferHandler 的 importData 方法时发生的。有谁知道这是否是某种错误或期望的行为?
我使用的是 Mac (OSX 10.8),如果有影响的话,Java 版本是 1.7.0_21。
提前致谢!
编辑:
这是一个简短的 SSCCE,供任何人测试。只需将文件拖到列表中即可观看控制台。
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.File;
import java.io.IOException;
import java.util.List;
import javax.swing.DefaultListModel;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JScrollPane;
import javax.swing.TransferHandler;
import javax.swing.TransferHandler.TransferSupport;
public class DNDIssue extends TransferHandler {
@Override
public boolean canImport(TransferSupport support) {
if (support.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
try {
Transferable transferable = support.getTransferable();
Object transferData = transferable.getTransferData(DataFlavor.javaFileListFlavor); // <-- this returns null
System.out.println(transferData); // null
} catch (IOException | UnsupportedFlavorException e) {
System.out.println("Unable to check for folders due to the following exception:\n" + e);
} finally {
return false;
}
} else {
return false;
}
}
public static void main(String[] args) {
// create window
JFrame window = new JFrame("DNDIssue");
window.setSize(640, 480);
window.setLocation(100, 100);
// create list with model and set transfer handler
JList<File> list = new JList<File>(new DefaultListModel<File>());
list.setTransferHandler(new DNDIssue());
// add enclosing scroll pane and display window
window.getContentPane().add(new JScrollPane(list));
window.setVisible(true);
}
}
最佳答案
我在 Windows 7 64 位上使用 JDK 1.7.0_21,您的 SSCCE 工作正常。
您可以尝试以下代码吗?
Transferable transferable = support.getTransferable(); System.out.println("----"); String mt = DataFlavor.javaFileListFlavor.getMimeType(); for(DataFlavor df: transferable.getTransferDataFlavors()) { System.out.println(df.getMimeType()); System.out.println(" "+df.getMimeType().equals(mt)); }
SSCCE 1.0:删除
SSCCE 1.1:覆盖
TransferHandler#importData(...)
版本InvalidDnDOperationException:无下降电流
java.awt.dnd.InvalidDnDOperationException: No drop current at sun.awt.dnd.SunDropTargetContextPeer.getTransferData(SunDropTargetContextPeer.java:245) at sun.awt.datatransfer.TransferableProxy.getTransferData(TransferableProxy.java:73) at java.awt.dnd.DropTargetContext$TransferableProxy.getTransferData(DropTargetContext.java:376) at FileTransferHandler.canImport(DNDIssueTest.java:64)
该问题可能与 Bug ID 6759788 https://bugs.java.com/bugdatabase/view_bug?bug_id=6759788 有关
SSCCE 1.2:忽略
InvalidDnDOperationException
import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.dnd.*;
import java.io.*;
import java.util.List;
import javax.swing.*;
import javax.swing.TransferHandler;
import javax.swing.TransferHandler.TransferSupport;
public class DNDIssueTest {
public JComponent makeUI() {
// create list with model and set transfer handler
JList<File> list = new JList<File>(new DefaultListModel<File>());
list.setDropMode(DropMode.INSERT);
list.setTransferHandler(new FileTransferHandler());
return new JScrollPane(list);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
@Override public void run() {
createAndShowGUI();
}
});
}
public static void createAndShowGUI() {
JFrame f = new JFrame();
f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
f.getContentPane().add(new DNDIssueTest().makeUI());
f.setSize(320, 240);
f.setLocationRelativeTo(null);
f.setVisible(true);
}
}
class FileTransferHandler extends TransferHandler {
private static final boolean DEBUG = true;
@SuppressWarnings("unchecked")
@Override public boolean importData(TransferSupport support) {
try {
List files = (List)support.getTransferable().getTransferData(DataFlavor.javaFileListFlavor);
System.out.println("importData");
if(!hasDirectory(files) && canImport(support)) {
JList list = (JList)support.getComponent();
DefaultListModel model = (DefaultListModel)list.getModel();
for(Object o: files) {
model.addElement(o);
}
return true;
}
} catch(Exception ex) {
ex.printStackTrace();
}
return false;
}
private boolean hasDirectory(List list) {
System.out.println("hasDirectory check");
for (Object o: list) {
if(o instanceof File) {
File file = (File) o;
if (file.isDirectory()) {
return true;
}
}
}
return false;
}
@Override public boolean canImport(TransferSupport support) {
if(!support.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
return false;
}
if(!DEBUG) return true;
Transferable transferable = support.getTransferable();
try {
Object transferData = transferable.getTransferData(DataFlavor.javaFileListFlavor);
//System.out.println(transferData); // null
System.out.println("canImport");
return !hasDirectory((List)transferData);
} catch (Exception e) {
//e.printStackTrace();
System.out.println("*** Ignore InvalidDnDOperationException ***");
return true;
}
}
}
- SSCCE 2.0:
DropTargetListener
版本
import java.awt.*;
import java.awt.datatransfer.*;
import java.awt.dnd.*;
import java.awt.event.*;
import java.io.*;
import java.util.List;
import javax.swing.*;
public class DNDIssueTest2 {
public JComponent makeUI() {
final DefaultListModel<File> model = new DefaultListModel<>();
JList<File> list = new JList<File>(model);
DropTargetListener dtl = new DropTargetAdapter() {
@Override public void dragOver(DropTargetDragEvent dtde) {
if(dtde.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
Transferable transferable = dtde.getTransferable();
Object transferData = null;
try {
transferData = transferable.getTransferData(DataFlavor.javaFileListFlavor);
} catch(Exception ex) {
dtde.rejectDrag();
return;
}
List<File> files = (List<File>)transferData;
for (int i = 0; i < files.size(); i++) {
File file = (File) files.get(i);
if (file.isDirectory()) {
dtde.rejectDrag();
return;
}
}
dtde.acceptDrag(DnDConstants.ACTION_COPY);
return;
}
dtde.rejectDrag();
}
@Override public void drop(DropTargetDropEvent dtde) {
try {
if(dtde.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
dtde.acceptDrop(DnDConstants.ACTION_COPY);
Transferable transferable = dtde.getTransferable();
List list = (List)transferable.getTransferData(DataFlavor.javaFileListFlavor);
for(Object o: list) {
if(o instanceof File) {
File file = (File) o;
model.addElement(file);
}
}
dtde.dropComplete(true);
return;
}
} catch(UnsupportedFlavorException ufe) {
ufe.printStackTrace();
} catch(IOException ioe) {
ioe.printStackTrace();
}
dtde.rejectDrop();
}
};
new DropTarget(list, DnDConstants.ACTION_COPY, dtl, true);
return new JScrollPane(list);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
@Override public void run() {
createAndShowGUI();
}
});
}
public static void createAndShowGUI() {
JFrame f = new JFrame();
f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
f.getContentPane().add(new DNDIssueTest2().makeUI());
f.setSize(320, 240);
f.setLocationRelativeTo(null);
f.setVisible(true);
}
}
关于java - 当调用 TransferHandler canImport 方法时,来自 jvm 外部的可传输数据的传输数据默认为 null 吗?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/16592166/