我该如何做到这一点?
这个解决方案可行。但是有一些注意事项。
我没有使用TransferHandler API。我不喜欢它,因为它太过限制性,但这只是我的个人想法(它所做的事情做得很好),所以这可能不能满足您的期望。
我使用了BorderLayout进行测试。如果您想使用其他布局,您需要尝试并弄清楚如何实现。拖放子系统确实提供有关鼠标指针(在移动和放置时)的信息。
那么我们需要什么:
DataFlavor。我选择这样做是因为它允许更大程度的限制。
public class PanelDataFlavor extends DataFlavor {
// This saves me having to make lots of copies of the same thing
public static final PanelDataFlavor SHARED_INSTANCE = new PanelDataFlavor();
public PanelDataFlavor() {
super(JPanel.class, null);
}
}
public class PanelTransferable implements Transferable {
private DataFlavor[] flavors = new DataFlavor[]{PanelDataFlavor.SHARED_INSTANCE};
private JPanel panel;
public PanelTransferable(JPanel panel) {
this.panel = panel;
}
@Override
public DataFlavor[] getTransferDataFlavors() {
return flavors;
}
@Override
public boolean isDataFlavorSupported(DataFlavor flavor) {
// Okay, for this example, this is overkill, but makes it easier
// to add new flavor support by subclassing
boolean supported = false;
for (DataFlavor mine : getTransferDataFlavors()) {
if (mine.equals(flavor)) {
supported = true;
break;
}
}
return supported;
}
public JPanel getPanel() {
return panel;
}
@Override
public Object getTransferData(DataFlavor flavor) throws UnsupportedFlavorException, IOException {
Object data = null;
if (isDataFlavorSupported(flavor)) {
data = getPanel();
} else {
throw new UnsupportedFlavorException(flavor);
}
return data;
}
}
“拖动手势监听器”
为此,我创建了一个简单的DragGestureHandler,它以“JPanel”作为要拖动的内容。这使得手势处理程序能够自我管理。
public class DragGestureHandler implements DragGestureListener, DragSourceListener {
private Container parent;
private JPanel child;
public DragGestureHandler(JPanel child) {
this.child = child;
}
public JPanel getPanel() {
return child;
}
public void setParent(Container parent) {
this.parent = parent;
}
public Container getParent() {
return parent;
}
@Override
public void dragGestureRecognized(DragGestureEvent dge) {
// When the drag begins, we need to grab a reference to the
// parent container so we can return it if the drop
// is rejected
Container parent = getPanel().getParent();
setParent(parent);
// Remove the panel from the parent. If we don't do this, it
// can cause serialization issues. We could overcome this
// by allowing the drop target to remove the component, but that's
// an argument for another day
parent.remove(getPanel());
// Update the display
parent.invalidate();
parent.repaint();
// Create our transferable wrapper
Transferable transferable = new PanelTransferable(getPanel());
// Start the "drag" process...
DragSource ds = dge.getDragSource();
ds.startDrag(dge, Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR), transferable, this);
}
@Override
public void dragEnter(DragSourceDragEvent dsde) {
}
@Override
public void dragOver(DragSourceDragEvent dsde) {
}
@Override
public void dropActionChanged(DragSourceDragEvent dsde) {
}
@Override
public void dragExit(DragSourceEvent dse) {
}
@Override
public void dragDropEnd(DragSourceDropEvent dsde) {
// If the drop was not successful, we need to
// return the component back to it's previous
// parent
if (!dsde.getDropSuccess()) {
getParent().add(getPanel());
getParent().invalidate();
getParent().repaint();
}
}
}
private DragGestureRecognizer dgr;
private DragGestureHandler dragGestureHandler;
@Override
public void addNotify() {
super.addNotify();
if (dgr == null) {
dragGestureHandler = new DragGestureHandler(this);
dgr = DragSource.getDefaultDragSource().createDefaultDragGestureRecognizer(
this,
DnDConstants.ACTION_MOVE,
dragGestureHandler);
}
}
@Override
public void removeNotify() {
if (dgr != null) {
dgr.removeDragGestureListener(dragGestureHandler);
dragGestureHandler = null;
}
dgr = null;
super.removeNotify();
}
public class DropHandler implements DropTargetListener {
@Override
public void dragEnter(DropTargetDragEvent dtde) {
// Determine if we can actually process the contents coming in.
// You could try and inspect the transferable as well, but
// there is an issue on the MacOS under some circumstances
// where it does not actually bundle the data until you accept the
// drop.
if (dtde.isDataFlavorSupported(PanelDataFlavor.SHARED_INSTANCE)) {
dtde.acceptDrag(DnDConstants.ACTION_MOVE);
} else {
dtde.rejectDrag();
}
}
@Override
public void dragOver(DropTargetDragEvent dtde) {
}
@Override
public void dropActionChanged(DropTargetDragEvent dtde) {
}
@Override
public void dragExit(DropTargetEvent dte) {
}
@Override
public void drop(DropTargetDropEvent dtde) {
boolean success = false;
// Basically, we want to unwrap the present...
if (dtde.isDataFlavorSupported(PanelDataFlavor.SHARED_INSTANCE)) {
Transferable transferable = dtde.getTransferable();
try {
Object data = transferable.getTransferData(PanelDataFlavor.SHARED_INSTANCE);
if (data instanceof JPanel) {
JPanel panel = (JPanel) data;
DropTargetContext dtc = dtde.getDropTargetContext();
Component component = dtc.getComponent();
if (component instanceof JComponent) {
Container parent = panel.getParent();
if (parent != null) {
parent.remove(panel);
}
((JComponent)component).add(panel);
success = true;
dtde.acceptDrop(DnDConstants.ACTION_MOVE);
invalidate();
repaint();
} else {
success = false;
dtde.rejectDrop();
}
} else {
success = false;
dtde.rejectDrop();
}
} catch (Exception exp) {
success = false;
dtde.rejectDrop();
exp.printStackTrace();
}
} else {
success = false;
dtde.rejectDrop();
}
dtde.dropComplete(success);
}
}
DropTarget dropTarget;
DropHandler dropHandler;
.
.
.
dropHandler = new DropHandler();
dropTarget = new DropTarget(pnlOne, DnDConstants.ACTION_MOVE, dropHandler, true);
个人而言,我在addNotify中初始化,在removeNotify中销毁
dropTarget.removeDropTargetListener(dropHandler);
关于addNotify的简短说明,我曾多次连续调用它,因此您可能需要仔细检查是否已经设置了拖放目标。
就这些。
您可能还会发现以下内容有趣:
http://rabbit-hole.blogspot.com.au/2006/05/my-drag-image-is-better-than-yours.html
http://rabbit-hole.blogspot.com.au/2006/08/drop-target-navigation-or-you-drag.html
http://rabbit-hole.blogspot.com.au/2006/04/smooth-jlist-drop-target-animation.html
即使只是出于兴趣,也不应该浪费时间去查看它们。
因此,在原始代码编写后的4年中,API的工作方式似乎发生了一些变化,至少在MacOS下会导致一些问题。
首先,DragGestureHandler
在调用DragSource#startDrag
时会导致NullPointerException
。这似乎与将容器的parent
引用设置为null
(通过从父容器中删除它)有关。
因此,我修改了dragGestureRecognized
方法,在调用DragSource#startDrag
之后从父面板中删除panel
...
@Override
public void dragGestureRecognized(DragGestureEvent dge) {
// When the drag begins, we need to grab a reference to the
// parent container so we can return it if the drop
// is rejected
Container parent = getPanel().getParent();
System.out.println("parent = " + parent.hashCode());
setParent(parent);
// Remove the panel from the parent. If we don't do this, it
// can cause serialization issues. We could overcome this
// by allowing the drop target to remove the component, but that's
// an argument for another day
// This is causing a NullPointerException on MacOS 10.13.3/Java 8
// parent.remove(getPanel());
// // Update the display
// parent.invalidate();
// parent.repaint();
// Create our transferable wrapper
System.out.println("Drag " + getPanel().hashCode());
Transferable transferable = new PanelTransferable(getPanel());
// Start the "drag" process...
DragSource ds = dge.getDragSource();
ds.startDrag(dge, null, transferable, this);
parent.remove(getPanel());
// Update the display
parent.invalidate();
parent.repaint();
}
我还修改了DragGestureHandler#dragDropEnd
方法。
@Override
public void dragDropEnd(DragSourceDropEvent dsde) {
// If the drop was not successful, we need to
// return the component back to it's previous
// parent
if (!dsde.getDropSuccess()) {
getParent().add(getPanel());
} else {
getPanel().remove(getPanel());
}
getParent().invalidate();
getParent().repaint();
}
以及 DropHandler#drop
@Override
public void drop(DropTargetDropEvent dtde) {
boolean success = false;
// Basically, we want to unwrap the present...
if (dtde.isDataFlavorSupported(PanelDataFlavor.SHARED_INSTANCE)) {
Transferable transferable = dtde.getTransferable();
try {
Object data = transferable.getTransferData(PanelDataFlavor.SHARED_INSTANCE);
if (data instanceof JPanel) {
JPanel panel = (JPanel) data;
DropTargetContext dtc = dtde.getDropTargetContext();
Component component = dtc.getComponent();
if (component instanceof JComponent) {
Container parent = panel.getParent();
if (parent != null) {
parent.remove(panel);
parent.revalidate();
parent.repaint();
}
((JComponent) component).add(panel);
success = true;
dtde.acceptDrop(DnDConstants.ACTION_MOVE);
((JComponent) component).invalidate();
((JComponent) component).repaint();
} else {
success = false;
dtde.rejectDrop();
}
} else {
success = false;
dtde.rejectDrop();
}
} catch (Exception exp) {
success = false;
dtde.rejectDrop();
exp.printStackTrace();
}
} else {
success = false;
dtde.rejectDrop();
}
dtde.dropComplete(success);
}
public class DragGestureHandler implements DragGestureListener, DragSourceListener, Serializable {
//...
}
public public class DropHandler implements DropTargetListener, Serializable {
//...
}
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.io.Serializable;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class Test implements Serializable {
public static void main(String[] args) {
new Test();;
}
public Test() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
ex.printStackTrace();
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
public TestPane() {
setLayout(new GridLayout(1, 2));
JPanel container = new OutterPane();
DragPane drag = new DragPane();
container.add(drag);
add(container);
add(new DropPane());
}
@Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
}
public class OutterPane extends JPanel {
public OutterPane() {
setBackground(Color.GREEN);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(100, 100);
}
}
}
DragPane
import java.awt.Color;
import java.awt.Dimension;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DragGestureRecognizer;
import java.awt.dnd.DragSource;
import javax.swing.JPanel;
public class DragPane extends JPanel {
private DragGestureRecognizer dgr;
private DragGestureHandler dragGestureHandler;
public DragPane() {
System.out.println("DragPane = " + this.hashCode());
setBackground(Color.RED);
dragGestureHandler = new DragGestureHandler(this);
dgr = DragSource.getDefaultDragSource().createDefaultDragGestureRecognizer(this, DnDConstants.ACTION_MOVE, dragGestureHandler);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(50, 50);
}
}
DropPane
import java.awt.Color;
import java.awt.Dimension;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DropTarget;
import javax.swing.JPanel;
public class DropPane extends JPanel {
DropTarget dropTarget;
DropHandler dropHandler;
public DropPane() {
setBackground(Color.BLUE);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(100, 100);
}
@Override
public void addNotify() {
super.addNotify(); //To change body of generated methods, choose Tools | Templates.
dropHandler = new DropHandler();
dropTarget = new DropTarget(this, DnDConstants.ACTION_MOVE, dropHandler, true);
}
@Override
public void removeNotify() {
super.removeNotify(); //To change body of generated methods, choose Tools | Templates.
dropTarget.removeDropTargetListener(dropHandler);
}
}
DragGestureHandler
、DropHandler
、PanelDataFlavor
和PanelTransferable
类保持不变,除了我上面提到的更改。所有这些类都是独立的外部类,否则会导致额外的NotSerializableException
问题。
有可能让DragGestureHandler
由正在拖拽的组件管理会导致整体问题,但我没有时间进行调查。
值得注意的是,我不提倡也不允许以这种方式操作组件,因为很容易陷入一种解决方案今天可以工作,明天就不能工作的情况。我更喜欢传输状态或数据-更加稳定。
我尝试了十几个基于原始答案中提出的相同概念的其他示例,这些示例仅传输状态并且没有问题,在尝试传输Component
时失败,直到应用了上述修复方法。
DragGestureHandler::dragGestureRecognized
方法中,变量称为 parent
,因此隐藏了实例的 parent
变量。这很容易解决。
当我使用给定的代码时,我会得到一个 java.awt.dnd.InvalidDnDOperationException: Cannot find top-level for the drag source component
。如果我将前几行代码(直到parent.repaint();
)放在方法的底部,那么异常就不再被抛出了。区别在于 new PanelTransferable(getPanel());
从哪里获取面板。为什么会这样? - Albertpublic class DragActionButton extends JButton {
private DragGestureRecognizer dgr;
private DragGestureHandler dragGestureHandler;
private JPanel actionPanel;
DragActionButton (JPanel actionPanel, String buttonText)
{
this.setText(buttonText);
this.actionPanel = actionPanel;
}
@Override
public void addNotify() {
super.addNotify();
if (dgr == null) {
dragGestureHandler = new DragGestureHandler(this.actionPanel);
dgr = DragSource.getDefaultDragSource().createDefaultDragGestureRecognizer(
this,
DnDConstants.ACTION_MOVE,
dragGestureHandler);
}
}
@Override
public void removeNotify() {
if (dgr != null) {
dgr.removeDragGestureListener(dragGestureHandler);
dragGestureHandler = null;
}
dgr = null;
super.removeNotify();
}
}
当创建按钮时,您将执行以下操作:
this.JButtonDragIt = new DragActionButton(this.JPanel_To_Drag, "button-text-here");