[英]Why are my panels not showing up in the JFrame
public class InputPanel extends JPanel{
public static int shapeType; //1: Rectangle; 2: Oval; 3: Line
public static boolean isFilled; //whether or not the shape is filled
public static Color color; //color of the shape
public InputPanel(){
JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT));
panel.setBackground(Color.GRAY);
setPreferredSize(new Dimension(200,500));
JButton rect = new JButton("Rectangle");
JButton oval = new JButton("Oval");
JButton line = new JButton("Line");
JRadioButton fill = new JRadioButton("Filled:");
JButton color1 = new JButton("Color..");
rect.addActionListener(new rectListener());
oval.addActionListener(new ovalListener());
line.addActionListener(new lineListener());
isFilled = fill.isSelected();
color1.addActionListener(new colorListener());
panel.add(rect);
panel.add(oval);
panel.add(line);
panel.add(fill);
panel.add(color1);
this.setVisible(true);
}
}
public class PaintPanel extends JPanel{
public static int x1, y1, x2, y2;
ArrayList<Shape> shapeList = new ArrayList<Shape>();
public PaintPanel(){
JPanel panel = new JPanel(new FlowLayout(FlowLayout.RIGHT));
panel.setBackground(Color.WHITE);
setPreferredSize(new Dimension(500, 500));
this.addMouseListener(new MouseAdapter() {
@Override public void mousePressed(MouseEvent e) {
PaintPanel.x1 = e.getX();
PaintPanel.y1 = e.getY();
}
@Override public void mouseReleased(MouseEvent e) {
PaintPanel.x2 = e.getX();
PaintPanel.y2 = e.getY();
if(InputPanel.shapeType == 1){
shapeList.add(new Rectangle(PaintPanel.x1, PaintPanel.y1, PaintPanel.x2, PaintPanel.y2, InputPanel.isFilled));
}
if(InputPanel.shapeType == 2){
shapeList.add(new Oval(PaintPanel.x1, PaintPanel.y1, PaintPanel.x2, PaintPanel.y2, InputPanel.isFilled));
}
if(InputPanel.shapeType == 3){
shapeList.add(new Line(PaintPanel.x1, PaintPanel.y1, PaintPanel.x2, PaintPanel.y2));
}
repaint();
}
});
this.setVisible(true);
}
@Override
public void paintComponent(Graphics g){
super.paintComponent(g);
for(Shape s : shapeList){
s.draw(g);
}
}
}
public class PaintGUI {
public static void main(String[] args){
JFrame frame = new JFrame("Shape Drawer!");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new InputPanel());
frame.add(new PaintPanel());
frame.pack();
frame.setVisible(true);
}
}
我很肯定我已经正确地创建了 JFrame 并且我的所有其他类都可以工作,但是这里肯定有一些东西我错过了......当我运行 main 方法时,我得到的只是一个灰色的盒子,它显然是一个正方形(500x500,在 PaintPanel 类中实例化。我做错了什么?
除了 Andrew 提到的,我注意到在InputPanel和PaintPanel中,您正在创建一个新的 JPanel。 当然,您正在向此面板添加新组件,但最后您不会将此 JPanel 本身添加到您的InputPanel或PaintPanel中。 因此,请确保在这些面板的构造函数中最后有一个add(panel)
。
另外,作为旁注,请记住 Swing 中的大多数操作都不是线程安全的,因此请在创建/与 UI 组件交互之前阅读“Swing 中的并发性”。 换句话说,用户界面的任何更新都必须发生在事件调度线程上,例如应用程序的启动:
public static void main(String[] args){
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame("Shape Drawer!");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//set the layout, add your panels
frame.pack();
frame.setVisible(true);
}
});
}
JFrame 默认使用 BorderLayout。
frame.add(new InputPanel());
frame.add(new PaintPanel());
相当于说,
frame.add(new InputPanel(), BorderLayout.CENTER);
frame.add(new PaintPanel(), BorderLayout.CENTER);
最终结果是最后添加的面板将是可见的,前提是您的其余代码工作正常。
必须将面板添加到框架中,使用:
this.add(panel);
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