Question

我正在尝试将三个矩形添加到BorderLayout的中心，我完全迷失了。我完成的程序需要在滑块移动时增加矩形的高度，但我想弄清楚如何将这三个矩形直接绘制到jpanel。我迷路了。我的代码如下。

 import java.awt.*;
 import javax.swing.*;
 import javax.swing.event.ChangeEvent;
 import javax.swing.event.ChangeListener;

 public class ShowColors extends JPanel
 {

public static void main(String args[])
{
    JFrame frame = new JFrame();

    JPanel main = new JPanel(new BorderLayout());
    main.setSize(2000, 1000);
    frame.setContentPane(main);

    JPanel jp1 = new JPanel(new GridLayout(0, 1));
    JPanel jp2 = new JPanel(new GridLayout(2,3));
    JPanel jp3 = new JPanel(new GridLayout(1, 3));

    jp1.setPreferredSize(new Dimension(90, 800));
    jp2.setPreferredSize(new Dimension(1000, 150));
    jp3.setPreferredSize(new Dimension(800, 600));

    JRadioButton rb1 = new JRadioButton("Decimal", true);
    JRadioButton rb2 = new JRadioButton("Binary");
    JRadioButton rb3 = new JRadioButton("Hex");
    JRadioButton rb4 = new JRadioButton("Octal");
    JButton jb1 = new JButton("RESET");

    ButtonGroup group = new ButtonGroup();
    group.add(rb1);
    group.add(rb2);
    group.add(rb3);
    group.add(rb4);

    JSlider jRed = new JSlider(0,255);
    JSlider jGreen = new JSlider(0,255);
    JSlider jBlue = new JSlider(0,255);

    jRed.setPaintLabels(true);
    jRed.setPaintTicks(true);
    jRed.setMinorTickSpacing(5);
    jRed.setMajorTickSpacing(50);
    jRed.setValue(0);

    jGreen.setPaintLabels(true);
    jGreen.setPaintTicks(true);
    jGreen.setMinorTickSpacing(5);
    jGreen.setMajorTickSpacing(50);
    jGreen.setValue(0);

    jBlue.setPaintLabels(true);
    jBlue.setPaintTicks(true);
    jBlue.setMinorTickSpacing(5);
    jBlue.setMajorTickSpacing(50);
    jBlue.setValue(0);

    JLabel labelR = new JLabel("Red", JLabel.CENTER);
    JLabel labelG = new JLabel("Green", JLabel.CENTER);
    JLabel lableB = new JLabel("Blue", JLabel.CENTER);

    jp1.add(rb1);
    jp1.add(rb2);
    jp1.add(rb3);
    jp1.add(rb4);
    jp1.add(jb1);

    jp2.add(labelR);
    jp2.add(labelG);
    jp2.add(lableB);
    jp2.add(jRed);
    jp2.add(jGreen);
    jp2.add(jBlue);

    main.add(jp1, BorderLayout.WEST);
    main.add(jp2, BorderLayout.SOUTH);

    frame.pack();
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}
public void paint(Graphics g)
{
    super.paint(g);
    g.drawRect(0, 0, 10, 20);
    g.setColor(Color.RED);
    g.fillRect(0, 0, 10, 20);

    g.drawRect(10, 0, 10, 20);
    g.setColor(Color.GREEN);
    g.fillRect(10, 0, 10, 20);

    g.drawRect(20, 0, 10, 20);
    g.setColor(Color.BLUE);
    g.fillRect(20, 0, 10, 20);
}

}

这是我的布局，我想要中心的矩形。 sample output

Answer 1

不要覆盖paint，在Swing中绘画是通过一系列复杂而复杂的方法实现的，这些方法很容易被破坏。相反，改为覆盖它的paintComponent方法。有关详细信息，请参阅Painting in AWT and Swing
话虽如此，不要将所有组件添加到要绘制的同一个面板上，否则最终会在所有组件下绘制。相反，创建一个单独的JPanel作为绘画表面，另一个JPanel作为控制器（包含控件和绘画表面）。使用setter和getter来更改绘制表面的状态。有关详细信息，请参阅Performing Custom Painting。
创建某种“可绘制”对象，它知道如何绘制自己以及绘制自身应该使用什么（颜色）
创建某种List（在绘画表面类中），它可以容纳您想要绘制的对象。在其中paintComponent，您将循环遍历列表并请求每个对象绘制自身，并将Graphics上下文传递给它。有关详细信息，请查看2D Graphics

此previous answer也可以提供帮助

Answer 2

我认为您只需要JPanel的简单子类并覆盖paintComponent()。这样的事情可以让你前进：

import javax.swing.*;
import java.awt.*;

 public class Canvas extends JPanel {

   // TODO member variables for rectangle size/color

   public void paintComponent(Graphics g) {
     super.paintComponent(g);
     g.fillRect(10,10,100,50);
     g.drawRect(10,80,100,50);
  }
}

修改：实际上，我猜你真的不需要一个“Canvas”类，你可以像@MadProgrammer建议的那样使用普通的JPanel。你需要的是一个封装Rectangle行为的类，它只是一个简单的JComponent，它被添加到保存三个矩形的JPanel。

这是一个有效的解决方案，为简洁起见，排除了导入：

public class ShowColors { class Rectangle extends JComponent implements ChangeListener { private JSlider slider; private Color color; public Rectangle(JSlider slider, Color color) { this.slider = slider; this.color = color; this.setPreferredSize(new Dimension(250, 250)); slider.addChangeListener(this); } public void paintComponent(Graphics g) { super.paintComponent(g); int value = slider.getValue(); g.setColor(color); g.fillRect(10,10,100,value); } @Override public void stateChanged(ChangeEvent arg0) { this.repaint(); } } public ShowColors() { JFrame frame = new JFrame(); JPanel main = new JPanel(new BorderLayout()); main.setSize(2000, 1000); frame.setContentPane(main); JPanel jp1 = new JPanel(new GridLayout(0, 1)); JPanel jp2 = new JPanel(new GridLayout(2, 3)); jp1.setPreferredSize(new Dimension(90, 800)); jp2.setPreferredSize(new Dimension(1000, 150)); JRadioButton rb1 = new JRadioButton("Decimal", true); JRadioButton rb2 = new JRadioButton("Binary"); JRadioButton rb3 = new JRadioButton("Hex"); JRadioButton rb4 = new JRadioButton("Octal"); JButton jb1 = new JButton("RESET"); ButtonGroup group = new ButtonGroup(); group.add(rb1); group.add(rb2); group.add(rb3); group.add(rb4); JSlider jRed = buildSlider(); JSlider jGreen = buildSlider(); JSlider jBlue = buildSlider(); JLabel labelR = new JLabel("Red", JLabel.CENTER); JLabel labelG = new JLabel("Green", JLabel.CENTER); JLabel lableB = new JLabel("Blue", JLabel.CENTER); jp1.add(rb1); jp1.add(rb2); jp1.add(rb3); jp1.add(rb4); jp1.add(jb1); jp2.add(labelR); jp2.add(labelG); jp2.add(lableB); jp2.add(jRed); jp2.add(jGreen); jp2.add(jBlue); JPanel canvas = new JPanel(); canvas.setLayout(new FlowLayout()); canvas.setPreferredSize(new Dimension(800, 600)); canvas.add(new Rectangle(jRed, Color.RED)); canvas.add(new Rectangle(jGreen, Color.GREEN)); canvas.add(new Rectangle(jBlue, Color.BLUE)); main.add(jp1, BorderLayout.WEST); main.add(jp2, BorderLayout.SOUTH); main.add(canvas, BorderLayout.EAST); frame.pack(); frame.setVisible(true); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } private static JSlider buildSlider() { JSlider slider = new JSlider(0, 255); slider.setPaintLabels(true); slider.setPaintTicks(true); slider.setMinorTickSpacing(5); slider.setMajorTickSpacing(50); slider.setValue(50); return slider; } public static void main(String args[]) { new ShowColors(); } }

这就是它的样子：

如何在java中为Jpanel添加3个矩形？

2 个答案: