本文介绍了使用Gridbag布局管理器在JPanel中拖动组件的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我正在尝试在JPanel中实现J组件的拖动。 JPanel必须使用Gridbag布局管理器。
我查看了许多拖动代码，包括这样的GUI构建器所获得的功能。交互式地移动组件。
I am trying to implement dragging of a J component within a JPanel. The JPanel has to use Gridbag layout manager.I reviewed many dragging codes, including Moving Windows. They all use component.setLocation(x, y); which has no effect when using Gridbag layout manager.I need help with alternative approach.
解决方案
if the JComponent is the only component in the JPanel, the task is not that complicated. Here is a small demo program that does it (with a bonus of re-sizing the component in response to mouse wheel events) :
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.LineBorder;
public class GridbagDragDemo extends JPanel {
/**
* Pixel width and height of positioned component.
*/
private float width, height;
/**
* Layout manger for this.
*/
private GridBagLayout gbl;
/**
* Layout horizontal weights for left and right gap, and component.
*/
private float leftWeight,xCompWeight, rightWeight;
/**
* Layout vertical weights for top and right gap, and component.
*/
private float topWeight,yCompWeight, bottomWeight;
/**
* Min and max weight values.
* These values can be changed to change the sensitivity of dragging.
* For better responsiveness W_MAX can be changed in respect to the JPanl's size.
* (also a different W_MAX can be set to horizontal and vertical axis.
*/
private float W_MIN = 0, W_MAX = 2;
/**
* Keep sum an even number for calculating (int) W_SUM/2
*/
private float W_SUM = W_MIN + W_MAX;
/**
* Represents the change in ratio between left / right weights
* and top/bottom weights for every pixel of mouse drag.
* The higher the factor the faster / more sensitive the
* component move is.
* Try different values to get the responsiveness you need.
*/
private float WEIGHT_DELTA = 0.01f;
/**
* Represents the change (in pixels) in component width and height
* and top/bottom weights for every mouse wheel notch.
* The higher the factor the faster / more sensitive the
* component resize.
* Try different values to get the responsiveness you need.
*/
private static final int ZOOM_FACTOR = 4;
/**
* Store mouse pressed position.
*/
private float pX, pY;
/**
* The dragged component
*/
private JComponent component;
public GridbagDragDemo() {
//set initial position to center
leftWeight = W_SUM/2 ; xCompWeight = 0; rightWeight = W_SUM/2;
topWeight = W_SUM/2 ; yCompWeight = 0; bottomWeight = W_SUM/2;
setPreferredSize(new Dimension(400, 300));
gbl = new GridBagLayout();
gbl.columnWidths = new int[] {0, 0, 0};
gbl.rowHeights = new int[] {0, 0, 0};
gbl.columnWeights = new double[]{leftWeight , xCompWeight, rightWeight };
gbl.rowWeights = new double[]{topWeight,yCompWeight, bottomWeight};
setLayout(gbl);
setBackground(Color.YELLOW);
component = new JPanel();
component.setPreferredSize(new Dimension(75,75));
component.setMinimumSize(new Dimension(15,15));
component.setMaximumSize(new Dimension(225,225));
component.setBackground(Color.ORANGE);
component.setBorder(new LineBorder(Color.black, 3));
//add drag listeners
component.addMouseMotionListener(new MouseMotionAdapter(){
@Override
public void mouseDragged(MouseEvent me) {
int mouseX = me.getXOnScreen();
int mouseY = me.getYOnScreen();
float moveX = mouseX - pX;
float moveY = mouseY - pY;
pX = mouseX;
pY = mouseY;
moveComp(moveX , moveY);
}
});
component.addMouseListener(new MouseAdapter() {
@Override
public void mousePressed(MouseEvent me) {
//store pressed position
pX = me.getXOnScreen();
pY = me.getYOnScreen();
}
});
//add resize listener
component.addMouseWheelListener(new MouseWheelListener() {
@Override
public void mouseWheelMoved(MouseWheelEvent me) {
//change sign so rolling "up" will be positive
reSizeComp(- me.getWheelRotation());
}
});
GridBagConstraints gbc_panel = new GridBagConstraints();
gbc_panel.fill = GridBagConstraints.BOTH;
gbc_panel.gridx = 1;
gbc_panel.gridy = 1;
add(component, gbc_panel);
width = component.getPreferredSize().width;
height = component.getPreferredSize().height;
}
private void moveComp(float moveX, float moveY) {
if(Math.abs(moveX)>0) {
leftWeight += WEIGHT_DELTA * moveX;
leftWeight = (float) setValueInRange(leftWeight, W_MIN, W_MAX);
rightWeight = W_SUM - leftWeight;
}
if(Math.abs(moveY)>0) {
topWeight += WEIGHT_DELTA * moveY;
topWeight = (float) setValueInRange(topWeight, W_MIN, W_MAX );
bottomWeight = W_SUM - topWeight;
}
gbl.columnWeights = new double[]{leftWeight,xCompWeight, rightWeight};
gbl.rowWeights = new double[]{topWeight, yCompWeight, bottomWeight};
refresh();
}
/**
*
*/
private void refresh() {
revalidate();
getParent().repaint();
}
private void reSizeComp(int notches) {
width += notches*ZOOM_FACTOR ; height += notches *ZOOM_FACTOR ;
//respect min / max component size
width = (float) setValueInRange(width, component.getMinimumSize().getWidth(),
component.getMaximumSize().getWidth() );
height = (float) setValueInRange(height, component.getMinimumSize().getHeight(),
component.getMaximumSize().getHeight() );
component.setPreferredSize(new Dimension((int)width,(int)height));
refresh();
}
private double setValueInRange(double value, double min, double max) {
value = (value < min ) ? min : value;
value = (value > max ) ? max : value;
return value;
}
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame("Test Gridbag drag");
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.setPreferredSize(new Dimension(400, 300));
frame.add(new GridbagDragDemo());
frame.pack();
frame.setVisible(true);
}
});
}
}
If the JPanel holds multiple components, it becomes a totally different ball game. With multiple components the functionality is similar to what you get using GUI builders like Eclipse' IDE Windowbuilder, where you can interactively move components.
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