我下载了一个在java中在2个JList之间拖放的示例，我正在使用自己的对象，一切都工作得很好，但是每次我放下一个对象时我都会遇到这个异常，并且不知道为什么.
java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to java.io.InputStream
at sun.awt.datatransfer.DataTransferer.translateTransferable(DataTransferer.java:1372)
at sun.lwawt.macosx.CDataTransferer.translateTransferable(CDataTransferer.java:131)
at sun.awt.datatransfer.DataTransferer$6.run(DataTransferer.java:2380)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:744)
at java.awt.EventQueue.access$400(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:697)
at java.awt.EventQueue$3.run(EventQueue.java:691)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:719)
at java.awt.EventQueue$4.run(EventQueue.java:717)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
这是我下载的示例。
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;
import javax.activation.ActivationDataFlavor;
import javax.activation.DataHandler;
import javax.swing.DefaultListModel;
import javax.swing.JComponent;
import javax.swing.JList;
import javax.swing.TransferHandler;
import javax.swing.TransferHandler.TransferSupport;
class ListItemTransferHandler extends TransferHandler {
private final DataFlavor localObjectFlavor;
private JList source = null;
private int[] indices = null;
private int addIndex = -1; //Location where items were added
private int addCount = 0; //Number of items added.
public ListItemTransferHandler() {
super();
localObjectFlavor = new ActivationDataFlavor(Object[].class, DataFlavor.javaJVMLocalObjectMimeType, "Array of items");
}
@Override
protected Transferable createTransferable(JComponent c) {
source = (JList) c;
indices = source.getSelectedIndices();
java.util.List transferedObjects = source.getSelectedValuesList();
return new DataHandler(transferedObjects.toArray(), localObjectFlavor.getMimeType());
}
@Override
public boolean canImport(TransferSupport info) {
return info.isDrop() && info.isDataFlavorSupported(localObjectFlavor);
}
@Override
public int getSourceActions(JComponent c) {
return MOVE; //TransferHandler.COPY_OR_MOVE;
}
@SuppressWarnings("unchecked")
@Override
public boolean importData(TransferSupport info) {
if (!canImport(info)) {
return false;
}
JList target = (JList) info.getComponent();
JList.DropLocation dl = (JList.DropLocation) info.getDropLocation();
DefaultListModel listModel = (DefaultListModel) target.getModel();
int index = dl.getIndex();
//boolean insert = dl.isInsert();
int max = listModel.getSize();
if (index < 0 || index > max) {
index = max;
}
addIndex = index;
try {
Object[] values = (Object[]) info.getTransferable().getTransferData(localObjectFlavor);
for (int i = 0; i < values.length; i++) {
int idx = index++;
listModel.add(idx, values[i]);
target.addSelectionInterval(idx, idx);
}
addCount = source.equals(target) ? values.length : 0;
return true;
} catch (UnsupportedFlavorException ufe) {
ufe.printStackTrace();
} catch (IOException ioe) {
ioe.printStackTrace();
}
return false;
}
@Override
protected void exportDone(JComponent c, Transferable data, int action) {
cleanup(c, action == MOVE);
}
private void cleanup(JComponent c, boolean remove) {
if (remove && indices != null) {
//If we are moving items around in the same list, we
//need to adjust the indices accordingly, since those
//after the insertion point have moved.
if (addCount > 0) {
for (int i = 0; i < indices.length; i++) {
if (indices[i] >= addIndex) {
indices[i] += addCount;
}
}
}
JList source = (JList) c;
DefaultListModel model = (DefaultListModel) source.getModel();
for (int i = indices.length - 1; i >= 0; i--) {
model.remove(indices[i]);
}
}
indices = null;
addCount = 0;
addIndex = -1;
}
}
主类
public class DragNdrop extends JPanel {
private DragNdrop() {
super(new BorderLayout());
JPanel p = new JPanel(new GridLayout(1,2,10,0));
TransferHandler h = new ListItemTransferHandler();
p.setBorder(BorderFactory.createTitledBorder("Drag & Drop between JLists"));
p.add(new JScrollPane(makeList(h)));
p.add(new JScrollPane(makeList(h)));
add(p);
setBorder(BorderFactory.createEmptyBorder(5,5,5,5));
setPreferredSize(new Dimension(320, 240));
}
private static JList<Color> makeList(TransferHandler handler) {
DefaultListModel<Color> listModel = new DefaultListModel<>();
listModel.addElement(Color.RED);
listModel.addElement(Color.BLUE);
listModel.addElement(Color.GREEN);
listModel.addElement(Color.CYAN);
listModel.addElement(Color.ORANGE);
listModel.addElement(Color.PINK);
listModel.addElement(Color.MAGENTA);
JList<Color> list = new JList<>(listModel);
list.setCellRenderer(new DefaultListCellRenderer() {
@Override public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
Component c = super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
((JLabel)c).setForeground((Color)value);
return c;
}
});
list.getSelectionModel().setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
list.setDropMode(DropMode.INSERT);
list.setDragEnabled(true);
list.setTransferHandler(handler);
return list;
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
@Override public void run() {
createAndShowGUI();
}
});
}
public static void createAndShowGUI() {
try{
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
}catch(ClassNotFoundException | InstantiationException |
IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
JFrame frame = new JFrame("DnDBetweenLists");
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.getContentPane().add(new DragNdrop());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
最佳答案
我也有类似的情况，其 ListModel 包含自定义类的实例的 JList。我尝试使类可序列化，但这并没有消除 ClassCastException。最终，我找到了 2003 年的一篇帖子，其中发帖者已经确定了解决方案:您不想只使用 DataFlavor 中的裸 MIME 类型；您应该使用 DataFlavor 中的 MIME 类型。您需要附加“;class=”。
https://lists.apple.com/archives/java-dev/2003/Apr/msg00458.html
即使在我的例子中，正在传输的是一个对象数组:
SpecialObject[] myData...
ActivationDataFlavor 的构造如下所示:
new ActivationDataFlavor(SpecialObject[].class, "application/x-java-specialobject-array;class=com.foo.bar.baz.SpecialObject", "Array of SpecialObject")
以这种方式构造 ActivationDataFlavor 可以消除异常。
关于java - ClassCastException 对象无法在拖放中转换为 InputStream，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/24544926/