Question

我有一个简单的程序来改变JFrame的背景和JLabel的前景。 JFrame上有一个JLabel和2个JButtons，一个用于更改单词，另一个用于更改背景。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;

import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JColorChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

@SuppressWarnings("serial")
public class ColorChooserDemo extends JPanel {

static JFrame frame;
JLabel label;
JButton button1, button2;

public ColorChooserDemo() {
    this.setBackground(new Color(255, 0, 255));
    setLayout(null);

    label = new JLabel("This is Text");
    button1 = new JButton("Set Word Color");
    button2 = new JButton("Set Background Color");

    add(label);
    add(button1);
    add(button2);

    label.setBounds(130, 10, 111, 15);
    button1.setBounds(100, 40, 200, 35);
    button2.setBounds(70, 90, 250, 35);

    button1.addActionListener(buttonPressed);
    button2.addActionListener(buttonPressed);
    button1.setActionCommand("words");
    button2.setActionCommand("back");

    label.setFont(new Font("Helvetica", Font.BOLD, 20));
    button1.setFont(new Font("Helvetica", Font.BOLD, 20));
    button2.setFont(new Font("Helvetica", Font.BOLD, 20));
}

AbstractAction buttonPressed = new AbstractAction() {
    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getActionCommand().equals("words")) {
            Color c = JColorChooser.showDialog(null, "Choose a Color", label.getForeground());
            if (c != null)
                label.setForeground(c);
        }
        if (e.getActionCommand().equals("back")) {
            Color c = JColorChooser.showDialog(null, "Choose a Color", label.getForeground());
            if (c != null)
                frame.getContentPane().setBackground(c);
        }
        repaint();
    }
};

public static void main(String[] args) {
    Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

    frame = new JFrame("ColorChooserDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add(new ColorChooserDemo());
    frame.setSize(400, 200);
    frame.setLocation((int) (screenSize.getWidth() - 400) / 2, (int) (screenSize.getHeight() - 200) / 2);
    frame.setResizable(false);
    frame.setVisible(true);
}

}

无论出于何种原因，frame.getContentPane().setBackground(c);都不起作用。我寻找解决方案，但没有任何工作，我不明白为什么。请帮忙。

- EDIT-- 我试过了repaint();但它仍然不起作用。它可能与frame是静态的吗？

Answer 1

这是一个很好的例子，例如static之类的东西会刺伤你......

所以，在你的代码中，你正在做......

frame.getContentPane().setBackground(c);

当你想改变背景颜色时，你必须问自己这个问题，contentPane是什么？由于您的组件从JPanel（不透明）延伸并设置了自己的背景颜色（this.setBackground(new Color(255, 0, 255));）（并且因为默认情况下JFrame使用了BorderLayout），因此您的组件覆盖了框架的整个内容区域，因此任何对frame.getContentPane().setBackground(c)的调用都不可见（因为您的面板覆盖了它）。

相反，你应该简单地使用......

setBackground(c);

澄清......

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JColorChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class ColorChooserDemo extends JPanel {

    JLabel label;
    JButton button1, button2;

    public ColorChooserDemo() {
        this.setBackground(new Color(255, 0, 255));
        setLayout(new GridBagLayout());

        label = new JLabel("This is Text");
        button1 = new JButton("Set Word Color");
        button2 = new JButton("Set Background Color");

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridwidth = GridBagConstraints.REMAINDER;

        add(label, gbc);
        add(button1, gbc);
        add(button2, gbc);

        button1.addActionListener(buttonPressed);
        button2.addActionListener(buttonPressed);
        button1.setActionCommand("words");
        button2.setActionCommand("back");

        label.setFont(new Font("Helvetica", Font.BOLD, 20));
        button1.setFont(new Font("Helvetica", Font.BOLD, 20));
        button2.setFont(new Font("Helvetica", Font.BOLD, 20));
    }

    AbstractAction buttonPressed = new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            if (e.getActionCommand().equals("words")) {
                Color c = JColorChooser.showDialog(null, "Choose a Color", label.getForeground());
                if (c != null) {
                    label.setForeground(c);
                }
            }
            if (e.getActionCommand().equals("back")) {
                System.out.println("...");
                Color c = JColorChooser.showDialog(null, "Choose a Color", getBackground());
                if (c != null) {
                    setBackground(c);
                }
            }
            repaint();
        }
    };

    public static void main(String[] args) {
        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

        JFrame frame = new JFrame("ColorChooserDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(new ColorChooserDemo());
        frame.setSize(400, 200);
        frame.setLocation((int) (screenSize.getWidth() - 400) / 2, (int) (screenSize.getHeight() - 200) / 2);
        frame.setResizable(false);
        frame.setVisible(true);
    }
}

我还强烈建议您查看Laying Out Components Within a Container，How to Use GridBagLayout和How to Use BorderLayout，了解有关layou管理API如何运作的详细信息

JFrame背景不变

1 个答案: