Question

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，但是我必须在这里找到一些东西... 当我运行main方法时，我得到的是一个灰色框，显然是一个正方形（500x500，在PaintPanel类中实例化。我做错了什么？

Answer 1

除了Andrew提到的内容之外，我注意到你在 InputPanel 和 PaintPanel 中都在创建一个新的JPanel。您肯定会在此面板中添加新组件，但最后您不会将此JPanel本身添加到 InputPanel 或 PaintPanel 。因此，请确保在这些面板的构造函数中最后有add(panel)。

另外，作为附注，请记住，Swing中的大多数操作都不是线程安全的，所以在创建/与UI组件交互之前，请阅读"Concurrency in Swing"。换句话说，对用户界面的任何更新都必须在事件派发线程上进行，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);             
        }
    });
}

Answer 2

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，如果其余代码工作正常，那么最后添加的Panel将是可见的。

为什么我的面板没有出现在JFrame中

2 个答案: