无法使用getGraphics绘制到JPanel [英] Can't draw to JPanel with getGraphics

问题描述

我想知道哪里出了问题.我之前已经做过，但是由于某种原因我这次无法使​​它正常工作.

I was wondering what went wrong. I've done this before but for some reason I can't get this to work this time.

我在Netbeans中设计了该项目.最相关的部分是initTiras方法，该方法被认为可以绘制某些东西，但事实并非如此.我包括了NetBeans生成的代码.

I designed the project in Netbeans. The most relevant part is the method initTiras, which is suppossed to draw something, but it doesn't. I included the code generated by NetBeans.

这是代码的最简化版本，但仍然没有显示任何内容.

Here's the most simplified version of the code, and still it paints nothing.

所以我在proyect中创建了一个新Frame.然后，我将JPanel放入其中(在设计模式下). JPanel称为ElPanel和JFrame LaFrame.

So I created a new Frame in the proyect. Then I put a JPanel in it (in desing mode). The JPanel's called ElPanel and the JFrame LaFrame.

这是主要班级:

package ElPackage;
public class Resistores {
    public static void main(String[] args) {
        LaFrame UnaFrame = new LaFrame();
        UnaFrame.setVisible(true);
    }   
}

在LaFrame类中:

Inside the LaFrame class:

package ElPackage;

import java.awt.Color;
import java.awt.Graphics;

public class LaFrame extends javax.swing.JFrame {
    public LaFrame () {
        initComponents();
        initTiras();
    }

    public void initTiras() {
        Graphics LasG = ElPanel.getGraphics();
        LasG.setColor(Color.WHITE);
        LasG.fillRect(10, 10, 30, 30);
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        ElPanel = new javax.swing.JPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setResizable(false);

        ElPanel.setBackground(new java.awt.Color(51, 0, 51));
        ElPanel.setForeground(new java.awt.Color(255, 255, 255));

        javax.swing.GroupLayout ElPanelLayout = new javax.swing.GroupLayout(ElPanel);
        ElPanel.setLayout(ElPanelLayout);
        ElPanelLayout.setHorizontalGroup(
            ElPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 400, Short.MAX_VALUE)
        );
        ElPanelLayout.setVerticalGroup(
            ElPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 300, Short.MAX_VALUE)
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(ElPanel, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(ElPanel, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );

        pack();
    }// </editor-fold>                        
    // Variables declaration - do not modify                     
    private javax.swing.JPanel ElPanel;
    // End of variables declaration                   
}

推荐答案

覆盖elPanel的paintComponent(Graphics g)方法，然后在其中添加代码.例如，请参见

Override paintComponent(Graphics g) method of elPanel and add your code there. See for example

使用Java命名约定-变量应以小写字母开头.

Use java naming convention - variables should start from lowercase letter.

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