大多数布局管理器都最适合使用组件的preferredSize,而大多数GUI最好允许包含的组件根据其内容或属性设置自己的preferredSizes。为了最大限度地利用这些布局管理器,请在使它们可见之前调用pack()在您的顶级容器(如JFrames)上,因为这将告诉这些管理器执行它们的操作--布置它们的组件。
通常情况下,当我需要更直接地设置一个组件的大小时,我会重写getPreferredSize并返回一个比super.preferredSize大的Dimension(如果没有,则返回超级值)。
例如,这里是一个我为
这个网站上的另一个问题创建的小拖动矩形应用程序:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class MoveRect extends JPanel {
private static final int RECT_W = 90;
private static final int RECT_H = 70;
private static final int PREF_W = 600;
private static final int PREF_H = 300;
private static final Color DRAW_RECT_COLOR = Color.black;
private static final Color DRAG_RECT_COLOR = new Color(180, 200, 255);
private Rectangle rect = new Rectangle(25, 25, RECT_W, RECT_H);
private boolean dragging = false;
private int deltaX = 0;
private int deltaY = 0;
public MoveRect() {
MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
addMouseListener(myMouseAdapter);
addMouseMotionListener(myMouseAdapter);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (rect != null) {
Color c = dragging ? DRAG_RECT_COLOR : DRAW_RECT_COLOR;
g.setColor(c);
Graphics2D g2 = (Graphics2D) g;
g2.draw(rect);
}
}
@Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
private class MyMouseAdapter extends MouseAdapter {
@Override
public void mousePressed(MouseEvent e) {
Point mousePoint = e.getPoint();
if (rect.contains(mousePoint)) {
dragging = true;
deltaX = rect.x - mousePoint.x;
deltaY = rect.y - mousePoint.y;
}
}
@Override
public void mouseReleased(MouseEvent e) {
dragging = false;
repaint();
}
@Override
public void mouseDragged(MouseEvent e) {
Point p2 = e.getPoint();
if (dragging) {
int x = p2.x + deltaX;
int y = p2.y + deltaY;
rect = new Rectangle(x, y, RECT_W, RECT_H);
MoveRect.this.repaint();
}
}
}
private static void createAndShowGui() {
MoveRect mainPanel = new MoveRect();
JFrame frame = new JFrame("MoveRect");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
请注意,我的主类是一个JPanel,并且我重写了JPanel的getPreferredSize方法:
public class MoveRect extends JPanel {
private static final int PREF_W = 600;
private static final int PREF_H = 300;
@Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
还要注意的是,当我展示我的GUI时,我会将它放入一个JFrame中,调用pack();
在JFrame上,设置它的位置,然后调用setVisible(true);
在我的JFrame上:
private static void createAndShowGui() {
MoveRect mainPanel = new MoveRect();
JFrame frame = new JFrame("MoveRect");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}