我正在尝试将拖放操作放入我的程序中；我发现以下示例说明了我正在尝试做的很多事情:
package sandbox;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.Cursor;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.LayoutManager;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
/**
* Example showing the use of a JLayeredPane to implement dragging an object
* across a JPanel containing other objects.
* <P>
* Basic idea: Create a JLayeredPane as a container, then put the JPanel containing
* the application's components or whatever in the JLayeredPane.DEFAULT_LAYER layer of that layered pane.
* The code is going to drag a JComponent object by calling JComponent.setPosition(x,y)
* on the component. When a mouse is clicked on the panel to start the dragging, put the
* component on the drag layer of the layered pane; as it is dragged, continue to call
* setPosition to move it. When the mouse is released, use the x.y position of the release
* to decide what to do with it next.
*
*/
public class ChessBoard extends JFrame implements MouseListener, MouseMotionListener
{
private static final long serialVersionUID = 1L;
JLayeredPane layeredPane;
JPanel chessBoard;
JLabel chessPiece;
int xAdjustment;
int yAdjustment;
public ChessBoard()
{
Dimension boardSize = new Dimension(600, 600);
// Use a Layered Pane for this application
layeredPane = new JLayeredPane();
layeredPane.setPreferredSize( boardSize );
layeredPane.addMouseListener( this );
layeredPane.addMouseMotionListener( this );
getContentPane().add(layeredPane);
//debug
LayoutManager lm = layeredPane.getLayout();
System.out.println("Layered pane layout name is " + (lm == null? "<null>" : lm.getClass().getName()));
// Add a chess board to the Layered Pane on the DEFAULT layer
chessBoard = new JPanel();
chessBoard.setLayout( new GridLayout(8, 8) );
chessBoard.setPreferredSize( boardSize );
chessBoard.setBounds(0, 0, boardSize.width, boardSize.height);
layeredPane.add(chessBoard, JLayeredPane.DEFAULT_LAYER);
// Build the Chess Board squares
// We use an 8x8 grid, and put a JPanel with BorderLayout on each square.
for (int i = 0; i < 8; i++)
{
for (int j = 0; j < 8; j++)
{
JPanel square = new JPanel( new BorderLayout() );
square.setBackground( (i + j) % 2 == 0 ? Color.gray : Color.white );
chessBoard.add( square );
}
}
// Add a few pieces to the board
// we do this with an ImageIcon that gets added to the square's panel.
ImageIcon duke = new ImageIcon("granary.gif"); // this is the image to add to each space.
addDuke(duke, 0);
addDuke(duke, 6);
addDuke(duke, 15);
addDuke(duke, 20);
}
private void addDuke(ImageIcon duke, int boardPosition)
{
JLabel pieceLabel = new JLabel(duke);
JPanel piecePanel = (JPanel)chessBoard.getComponent(boardPosition);
piecePanel.add(pieceLabel);
}
/*
** Add the selected chess piece to the dragging layer so it can be moved
*/
public void mousePressed(MouseEvent e)
{
// get the component where the user pressed; iff that's not a panel,
// we'll put it on the dragging layer.
chessPiece = null; // change1 swap the change1 lines
// chessPiece = new JLabel(new ImageIcon("house1x1.gif")); // change1
Component c = chessBoard.findComponentAt(e.getX(), e.getY());
if (c instanceof JPanel) return;
// get the location of the panel containing the image panel, i.e.,
// the square's panel. we adjust the location to which we move the
// piece by this amount so the piece doesn't 'snap to' the cursor
// location.
Point parentLocation = c.getParent().getLocation();
xAdjustment = parentLocation.x - e.getX();
yAdjustment = parentLocation.y - e.getY();
chessPiece = (JLabel)c; // change2 - comment out
chessPiece.setLocation(e.getX() + xAdjustment, e.getY() + yAdjustment);
layeredPane.add(chessPiece, JLayeredPane.DRAG_LAYER); // evidently this removes it from the default layer also.
layeredPane.setCursor(Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR));
}
/*
** Move the chess piece around
*/
public void mouseDragged(MouseEvent me)
{
if (chessPiece == null) return;
// The drag location should be within the bounds of the chess board
int x = me.getX() + xAdjustment;
int xMax = layeredPane.getWidth() - chessPiece.getWidth();
x = Math.min(x, xMax);
x = Math.max(x, 0);
int y = me.getY() + yAdjustment;
int yMax = layeredPane.getHeight() - chessPiece.getHeight();
y = Math.min(y, yMax);
y = Math.max(y, 0);
chessPiece.setLocation(x, y); // evidently this works for whatever layer contains the piece.
// also, the layout manager of its new home is evidently not the same as lower layers.
}
/*
** Drop the chess piece back onto the chess board
*/
public void mouseReleased(MouseEvent e)
{
layeredPane.setCursor(null);
if (chessPiece == null) return;
// Make sure the chess piece is no longer painted on the layered pane
chessPiece.setVisible(false);
layeredPane.remove(chessPiece);
chessPiece.setVisible(true);
// The drop location should be within the bounds of the chess board
int xMax = layeredPane.getWidth() - chessPiece.getWidth();
int x = Math.min(e.getX(), xMax);
x = Math.max(x, 0);
int yMax = layeredPane.getHeight() - chessPiece.getHeight();
int y = Math.min(e.getY(), yMax);
y = Math.max(y, 0);
Component c = chessBoard.findComponentAt(x, y);
Container parent = null;
if (c instanceof JLabel)
{
parent = c.getParent(); // there's a piece on the square already; remove it from the panel.
parent.remove(0);
}
else
{
parent = (Container)c;
}
parent.add( chessPiece ); // this adds the piece back to the default layer
parent.validate();
}
public void mouseClicked(MouseEvent e) {}
public void mouseMoved(MouseEvent e) {}
public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
public static void main(String[] args)
{
JFrame frame = new ChessBoard();
frame.setDefaultCloseOperation( DISPOSE_ON_CLOSE );
frame.setResizable( false );
frame.pack();
frame.setLocationRelativeTo( null );
frame.setVisible(true);
}
}
这适用于棋盘的情况，即允许用户将棋盘上的任何棋子拖动到不同的方格。
在我正在编写的应用程序中，被拖动的项目在用户单击开始拖动操作的某些内容之前并不存在。我无法弄清楚如何进行该创作并将其显示出来。
我当前的尝试是在标记为“change1”和“change2”的行上；将这两行与“change1”交换，并用“change2”注释掉这一行。换句话说，按下鼠标时创建 JLabel，并(希望)拖动它。但是当我运行它时，图像在按下或拖动期间不会显示，但会显示在拖动结束时的正方形上。
我在这里错过了什么？我对 JLayeredPane 有点困惑，javadoc 说它将遵循布局规则，但没有说明布局规则是否适用于所有层上的所有组件，或者仅适用于底部，或者适用于所有层但单独，什么？我不认为这是布局问题，但我不知道出了什么问题。我需要在某处进行某种 UI 更新吗？我认为添加该组件会使面板失效。
最佳答案
原始代码是假设您单击一个棋子而编写的。
现在您想要单击一个空单元格，这将需要进行以下更改。
- 棋盘由每个单元格中的 JPanel 组成。一些单元格将包含一个代表棋子的 JLabel。 mousePressed 事件中的当前逻辑期望您单击 JLabel，否则将跳过某些处理。
您需要删除:
//if (c instanceof JPanel) return;
您需要给它一个大小:
chessPiece.setSize( chessPiece.getPreferredSize() );
您需要调整此逻辑以使其再次相对于父面板:
//Point parentLocation = c.getParent().getLocation();
Point parentLocation = c.getLocation();
我更新的 mousePressed 方法如下所示:
public void mousePressed(MouseEvent e)
{
// get the component where the user pressed; iff that's not a panel,
// we'll put it on the dragging layer.
//chessPiece = null; // change1 swap the change1 lines
chessPiece = new JLabel(new ImageIcon("dukewavered.gif")); // change1
chessPiece.setSize( chessPiece.getPreferredSize() );
Component c = chessBoard.findComponentAt(e.getX(), e.getY());
//if (c instanceof JPanel) return;
// get the location of the panel containing the image panel, i.e.,
// the square's panel. we adjust the location to which we move the
// piece by this amount so the piece doesn't 'snap to' the cursor
// location.
//Point parentLocation = c.getParent().getLocation();
Point parentLocation = c.getLocation();
xAdjustment = parentLocation.x - e.getX();
yAdjustment = parentLocation.y - e.getY();
//chessPiece = (JLabel)c; // change2 - comment out
chessPiece.setLocation(e.getX() + xAdjustment, e.getY() + yAdjustment);
layeredPane.add(chessPiece, JLayeredPane.DRAG_LAYER); // evidently this removes it from the default layer also.
layeredPane.setCursor(Cursor.getPredefinedCursor(Cursor.MOVE_CURSOR));
}
请注意，上述更改将破坏能够拖动现有标签的旧功能。如果您需要两者的功能，那么您的逻辑将取决于您单击 JLabel(在这种情况下您使用旧逻辑)还是单击 JPanel(在这种情况下您使用较新的逻辑)。
关于java - 尝试使用 JLayeredPane 拖动某些内容，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/64598967/