我正在尝试 Java SE 7 中 JList 的拖放功能。问题是,一旦我为 JList 设置了 DropTarget,我的 TransferHandler 实现中的 canImport() 方法就会停止调用。这是演示问题的简化代码:
主类:
import javax.swing.ListSelectionModel;
public class TestDragDrop extends javax.swing.JFrame {
public TestDragDrop() {
initComponents();
lstTest.setDragEnabled(true);
lstTest.setTransferHandler(new MyTransferHandler());
// try to comment and uncomment the following line:
lstTest.setDropTarget(new MyDropTarget());
// - commented => canImport() is called during drag gesture
// - uncommented => canImport() is not called during drag gesture
lstTest.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
}
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
scroll1 = new javax.swing.JScrollPane();
lstTest = new javax.swing.JList();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
lstTest.setModel(new javax.swing.AbstractListModel() {
String[] strings = { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" };
public int getSize() { return strings.length; }
public Object getElementAt(int i) { return strings[i]; }
});
scroll1.setViewportView(lstTest);
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(scroll1, javax.swing.GroupLayout.DEFAULT_SIZE, 249, Short.MAX_VALUE)
.addContainerGap())
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(scroll1, javax.swing.GroupLayout.DEFAULT_SIZE, 174, Short.MAX_VALUE)
.addContainerGap())
);
pack();
}// </editor-fold>
public static void main(String args[]) {
new TestDragDrop().setVisible(true);
}
// Variables declaration - do not modify
private javax.swing.JList lstTest;
private javax.swing.JScrollPane scroll1;
// End of variables declaration
}
我的传输处理程序实现:
import java.awt.datatransfer.Transferable;
import javax.swing.JComponent;
import javax.swing.JList;
import javax.swing.TransferHandler;
public class MyTransferHandler extends TransferHandler {
@Override
public int getSourceActions(JComponent component) {
return COPY_OR_MOVE;
}
@Override
protected Transferable createTransferable(JComponent component) {
if(component instanceof JList) {
return new MyTransferable(new String("TestObject"));
}
return null;
}
@Override
public boolean canImport(TransferHandler.TransferSupport support) {
System.out.println("canImport()");
return true;
}
@Override
public boolean importData(TransferHandler.TransferSupport support) {
System.out.println("importData()");
return true;
}
}
我的可转让实现:
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;
public class MyTransferable implements Transferable {
private final Object object;
public MyTransferable(Object object) {
this.object = object;
}
@Override
public DataFlavor[] getTransferDataFlavors() {
return new DataFlavor[] { DataFlavor.javaFileListFlavor };
}
@Override
public boolean isDataFlavorSupported(DataFlavor flavor) {
return flavor.equals(DataFlavor.javaFileListFlavor);
}
@Override
public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
if(!isDataFlavorSupported(flavor)) {
throw new UnsupportedFlavorException(flavor);
}
return object;
}
}
我的放置目标实现:
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetDropEvent;
public class MyDropTarget extends DropTarget {
@Override
public synchronized void drop(DropTargetDropEvent evt) {
evt.acceptDrop(evt.getDropAction());
if(evt.isLocalTransfer()) {
System.out.println("local transfer");
} else {
System.out.println("extern transfer");
}
evt.dropComplete(true);
}
}
如果行 lstTest.setDropTarget(new MyDropTarget());主类中的 被关闭/注释, MyTransferHandler 中的 canImport() 方法在拖动手势期间按预期调用。但是一旦我取消注释这一行,在拖动过程中就不会调用 canImport() 方法...
有人知道为什么不再调用 canImport() 吗?
任何帮助高度赞赏!提前谢谢了。
最佳答案
setTransferHandler
如果不存在,则安装新的 DropTarget
并将设置它以使用指定的 TransferHandler
。之后用另一个 DropTarget
替换这个 DropTarget
将破坏这个设置。将自定义 TransferHandler
与以 Swing 方式工作的 ojit_code 结合起来相当棘手。以下将完成这项工作:
jComponent.setTransferHandler(new MyTransferHandler());
DropTarget original = jComponent.getDropTarget();// the Swing DropTarget
MyDropTarget myDropTarget = new MyDropTarget();
myDropTarget.addDropTargetListener(original);// delegate for original behavior
jComponent.setDropTarget(myDropTarget);