在Netbeans GUI中重写paintComponent [英] Override paintComponent in Netbeans GUI

问题描述

我已经在我的Netbeans生成的GUI中添加了一个JPanel，并添加了一个覆盖paintComponent并绘制一个红色小框的JPanel BoxThing，但是它不显示，甚至从未调用paintComponent.如果我实例化我自己的JFrame并放入一个包含BoxThing的JPanel，它将正常工作.

I've added a JPanel to my Netbeans generated GUI, and add a JPanel BoxThing that overrides paintComponent and draws a small red box, but it doesn't display, paintComponent never even gets invoked. If I instantiate my own JFrame and put a JPanel containing a BoxThing in it, it works fine.

我已经在随机论坛上再问过几次这个问题，而人们没有回答这个问题，而是指向

I've seen this question asked a few other times on random forums, and the people don't answer the question, instead they point to the custom painting tutorial, which obviously doesn't help.

我先尝试使用Netbeans 5.5，然后又切换到Netbeans 6.8，同样的问题.

I tried with Netbeans 5.5 first, then switched to Netbeans 6.8, same issue.

Main.java

Main.java

package MadProGUI9000;

public class Main extends javax.swing.JFrame {

    /** Creates new form Main */
    public Main() {
        initComponents();
        panel.add(new BoxThing());
    }

    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {

        panel = new javax.swing.JPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        panel.setBorder(javax.swing.BorderFactory.createLineBorder(new java.awt.Color(0, 0, 0)));

        javax.swing.GroupLayout panelLayout = new javax.swing.GroupLayout(panel);
        panel.setLayout(panelLayout);
        panelLayout.setHorizontalGroup(
            panelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 260, Short.MAX_VALUE)
        );
        panelLayout.setVerticalGroup(
            panelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 185, Short.MAX_VALUE)
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(69, 69, 69)
                .addComponent(panel, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(69, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(45, 45, 45)
                .addComponent(panel, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(68, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>

    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Main().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify
    private javax.swing.JPanel panel;
    // End of variables declaration

}

BoxThing.java

BoxThing.java

package MadProGUI9000;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;

/**
 * A component with a red box in the center.
 */
public class BoxThing extends JPanel {

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        Dimension size = getSize();

        int rX = (size.width - 5)/2;
        int rY = (size.height - 5)/2;

        g.setColor(Color.RED);
        g2.fillRect(rX, rY, 5, 5);
    }

    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                JFrame frame = new JFrame("BoxThing demo");
                JPanel panel = new JPanel();
                frame.add(panel);
                panel.add(new BoxThing());
                frame.setVisible(true);
                panel.setPreferredSize(new Dimension(100, 100));
                frame.pack();
            }
        });
    }

}

如您所见，只要运行BoxThing.java的main，它就会起作用.如果您运行Netbeans GUI，它将无法正常工作.因此，如何将自定义组件添加到Netbeans生成的Swing GUI中?

As you can see, it works if you just run BoxThing.java's main. If you run the Netbeans GUI, it wont work. So, how can I add custom components to a Netbeans generated Swing GUI?

推荐答案

这是组布局的工作方式.它将屏幕空间划分为Groups.在布局过程中，它循环遍历各组以确定每个组件的边界.当您将面板添加到容器时，它没有添加到任何组中，因此从未指定大小或位置.结果，它的大小为(0,0)，并且从未被绘制.

That's the way Group layout works. It divides the screen real estate up into Groups. During layout it cycles through the groups to determine the bounds for each component. When you added your panel to the container, it was not added to any group, and so was never given a size or location. As a result it has a size of (0,0) and is never painted.

您可以通过设置大小使其显示，但是由于布局中并未考虑它的大小，因此很有可能最终会与其他组件重叠.

You can make it appear by setting a size, but as it's not being considered in the layout, it will most likely wind up overlapping with other components.

要完成所需的操作，需要将panel的布局设置为其他内容，例如BorderLayout.例如:

To accomplish what you want, you need to set panel's layout to something else, like BorderLayout. For example:

public Main() {
    initComponents();
    panel.setLayout(new BorderLayout());
    panel.add(new BoxThing(), Borderlayout.CENTER);
}

这篇关于在Netbeans GUI中重写paintComponent的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！