Question

我正在尝试制作一个具有显示多边形和两个按钮的窗口的程序。多边形从3个点（三角形）开始，允许用户按“+”和“ - ”按钮来添加或减去多边形的边。这是我的代码：

在TestPolygonBox中：

package testpolygonbox
import javax.swing.*;
import java.awt.*;
public class TestPolygonBox extends JFrame {


public TestPolygonBox(){
    setLayout(new BorderLayout(5,5));
    add(new PolygonBox ());
}
public static void main(String[] args) {
    TestPolygonBox frame = new TestPolygonBox();
    frame.setTitle("Polygon Box");
    frame.setSize(400,420);
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);

}
}

接下来是控制类：

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

public class PolygonBox extends JPanel {
private JButton jbtEnlarge = new JButton("+");
private JButton jbtShrink = new JButton("-");
private PolygonPanel polygonPanel = new PolygonPanel();

public PolygonBox(){
    JPanel panel = new JPanel();
    panel.add(jbtEnlarge);
    panel.add(jbtShrink);
     setLayout(new BorderLayout());
    this.add(polygonPanel,BorderLayout.CENTER);
    this.add(panel, BorderLayout.SOUTH);

    jbtEnlarge.addActionListener(new EnlargeListener());
    jbtShrink.addActionListener(new ShrinkListener());
}


class EnlargeListener implements ActionListener{
@Override
public void actionPerformed(ActionEvent e){
    polygonPanel.enlarge();
   }
}
class ShrinkListener implements ActionListener{
@Override
public void actionPerformed(ActionEvent e){
    polygonPanel.shrink();
}
}
}

class PolygonPanel extends JPanel{
private int polygonSides = 3;

/** Add side to the polygon*/
public void enlarge(){
    polygonSides++;
    repaint();
}
public void shrink(){
    polygonSides--;
    repaint();
}
  @Override /** Draw requested Shape*/
protected void paintComponent(Graphics g){

    int frameWidth = getWidth() / 2;
    int frameHeight = getHeight() / 2;
    int radius = (int)(Math.min(getWidth(),getHeight())* 0.4);
    int xCenter = getWidth() / 2;
    int yCenter = getHeight() / 2;


    g.setColor(Color.BLUE);
    Polygon polygon = new Polygon();

    polygon.addPoint(xCenter + radius, yCenter);
                polygon.addPoint((int)(xCenter + radius * Math.cos(2 * Math.PI/polygonSides)),
                        (int)(yCenter - radius * Math.sin(2 * Math.PI / polygonSides)));
                for (int polygonPoint = 2; polygonPoint <= polygonSides; polygonPoint++){
                    polygon.addPoint((int)(xCenter + radius * Math.cos(polygonPoint * 2 * Math.PI/polygonSides)),
                        (int)(yCenter - radius * Math.sin(polygonPoint * 2 * Math.PI / polygonSides)));
                }

    g.fillPolygon(polygon);
}


}

当我尝试运行此程序时，我收到错误：线程“main”中的异常java.lang.IllegalArgumentException：向容器添加窗口在java.awt.Container.checkNotAWindow（Container.java:483）在java.awt.Container.addImpl（Container.java:1084） at java.awt.Container.add（Container.java:998）在javax.swing.JFrame.addImpl（JFrame.java:562）在java.awt.Container.add（Container.java:410）在testpolygonbox.TestPolygonBox。（TestPolygonBox.java:21）在testpolygonbox.TestPolygonBox.main（TestPolygonBox.java:24） Java结果：1

如果有人能告诉我在哪个窗口添加到容器中吗？我不确定我做错了什么。

Answer 1

PolygonBox是JFrame窗口，但您将其添加到另一个JFrame。更改类，使其扩展JPanel。

public class PolygonBox extends JPanel {

Answer 2

您的代码存在4个严重问题。

您没有在事件派发线程（EDT）中执行Swing代码。你的主要看起来像这样：
```
public static void main(String args[])
{
    SwingUtilities.invokeLater(new Runnable()
    {
        public void run()
        {
            initializeGUI();
        }
    }
}
```
即使Swing Hello World - 最简单的Swing程序 - 这也是非常重要的。如果你想知道为什么会这样，请阅读concurrency tutorial。简而言之，如果一旦程序变得更大，更复杂，你就不能正确地做到这一点，你会看到Swing类中出现很多不一致，不可重现的异常和错误，你无法追踪。
其次，正如Reimeus所说，你不能把框架放在另一个框架内，PolygonBox必须是JPanel。
第三，您没有正确填充面板。看看这段代码：
```
JPanel panel = new JPanel();
panel.add(jbtEnlarge);
panel.add(jbtShrink);
```
这段代码看起来很怪异，而且确实如此。当你看到它时弹出的问题是：“这些按钮在哪里添加？”那么在panel当然，但在面板中？这取决于面板使用的布局。那个面板的布局是什么？好吧，因为您没有明确指定它正在使用JPanels的默认布局：BorderLayout。边框布局panel.add(component);相当于panel.add(component, BorderLayout.CENTER);。但是你不能把两个组件放在CENTER中，你可以把一个面板包含很多组件或者其他什么，但是你不能直接放两个组件，这就是为什么那个代码不起作用的原因。那么你如何填充面板？选择一个布局学习使用它，然后以适当的方式添加组件。例如，我将使用GridLayout。
执行此操作
```
JPanel panel = new JPanel(new GridLayout(1, 2));
panel.add(_enlargeButton);
panel.add(_shrinkButton);
```
使用Grid布局，因为我说我想要一个网格1x2，这些添加是正确的，因为面板现在知道他必须将组件放在网格的每个单元格中。
最后你会看到有绘画问题：多边形没有被删除，它们被涂在一起，你可能会看到面板中按钮的图像...这是因为你有在paintComponent方法中调用super.paintComponent(g)。事实是代码绘制了一个多边形，是的，但是你还必须完成组件为绘制自身所做的所有其他工作，所以你要做的第一件事就是调用你要覆盖的原始代码，然后绘制你的组件。有关为何如此工作的详尽教程，请参阅Painting in AWT and Swing。

尽管如此，更改一些变量名称以遵循Java约定并重新格式化代码以实现更好的组织。这是你的固定计划：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Polygon;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class TestPolygonBox extends JFrame
{
    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable() { //Error 1: executing Swing code outside the EDT fixed
            public void run()
            {
                TestPolygonBox frame = new TestPolygonBox();
                frame.setVisible(true);
            }
        });
    }

    public TestPolygonBox()
    {
        super("Polygon Box"); //this is JFrame("title") since we are extending a frame
        setLayout(new BorderLayout());//this line doesn't actually do nothing since the frame already usesk BorderLayout by default

        add(buildPolygonBoxPanel());

        setSize(400, 420);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    }


    private JPanel buildPolygonBoxPanel() //Error 2: PolygonBox has to be a panel, also I made it into a mthod returning the panel instead of a whole class since it was unnecessary.
    {
        JPanel polygonBox = new JPanel(new BorderLayout());

        _polygonPanel = new PolygonPanel();

        JPanel buttonsPanel = new JPanel(new GridLayout(1, 2)); //Error 4 adding the buttons properly to a panel.
        _enlargeButton = new JButton("+1");
        _enlargeButton.addActionListener(new EnlargeListener());
        _shrinkButton = new JButton("-1");
        _shrinkButton.addActionListener(new ShrinkListener());
        buttonsPanel.add(_enlargeButton);
        buttonsPanel.add(_shrinkButton);

        polygonBox.add(_polygonPanel, BorderLayout.CENTER);
        polygonBox.add(buttonsPanel, BorderLayout.SOUTH);

        return polygonBox;
    }

    class EnlargeListener implements ActionListener
    {
        @Override
        public void actionPerformed(ActionEvent e)
        {
            _polygonPanel.enlarge();
        }
    }

    class ShrinkListener implements ActionListener
    {
        @Override
        public void actionPerformed(ActionEvent e)
        {
            _polygonPanel.shrink();
        }
    }

    private JButton _enlargeButton;
    private JButton _shrinkButton;
    private PolygonPanel _polygonPanel;
}

class PolygonPanel extends JPanel
{
    private int _polygonSides = 3;

    /** Add side to the polygon */
    public void enlarge()
    {
        _polygonSides++;
        repaint();
    }

    public void shrink()
    {
        if (_polygonSides > 3) _polygonSides--;
        repaint();
    }

    @Override
    /** Draw requested Shape*/
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g); //Error 4 fixed, call super.paintComponent

        int radius = (int) (Math.min(getWidth(), getHeight()) * 0.4);
        int xCenter = getWidth() / 2;
        int yCenter = getHeight() / 2;

        g.setColor(Color.BLUE);
        Polygon polygon = new Polygon();

        polygon.addPoint(xCenter + radius, yCenter);
        polygon.addPoint((int) (xCenter + radius * Math.cos(2 * Math.PI / _polygonSides)), (int) (yCenter - radius * Math.sin(2 * Math.PI / _polygonSides)));
        for (int polygonPoint = 2; polygonPoint <= _polygonSides; polygonPoint++)
        {
            polygon.addPoint((int) (xCenter + radius * Math.cos(polygonPoint * 2 * Math.PI / _polygonSides)), (int) (yCenter - radius * Math.sin(polygonPoint * 2 * Math.PI / _polygonSides)));
        }

        g.fillPolygon(polygon);
    }
}

只需复制并执行它，它看起来像这样：

TestPolygonBox

Java多边形调整大小

2 个答案: