对象在调整大小时以及窗口最小化时消失

Question

i need some help with this code. I already have the functions of paint the objects and clear the objects from the window but how i can make that when i make a resize or when i minimize the windows the objects doesn't disappear?

This is the code i have at the moment:

public class miClass implements ActionListener{
JFrame ventana;
JPanel panel;
JButton p,c;
Graphics g;
Image img;
Font font1,font2,font3;

public miClass(){
    ventana = new JFrame("Aplicacion.");
    p = new JButton("P");
    c = new JButton("C");
    panel = new JPanel();
    ventana.setLayout(null);
    ventana.setBounds(100,100,600,600);
    ventana.getContentPane().add(panel);
    ventana.add(p);
    p.addActionListener(this);
    c.addActionListener(this);
    p.setBounds(20,20,120,45);
    ventana.add(c);
    c.setBounds(200,20,120,45);
    ventana.setFocusable(true);
    ventana.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    ventana.setVisible(true);
}

public void actionPerformed(ActionEvent e) {
    g = ventana.getGraphics();
    Toolkit tool = Toolkit.getDefaultToolkit();
    img = tool.getImage("prueba.png");
    g.drawImage(img,0,100,null);

    font1 = new Font("Helvetica",Font.PLAIN,22);
    g.setFont(font1);
    g.drawString("Hola", 100, 300);

    font2 = new Font("TimesRoman",Font.BOLD,20);
    g.setFont(font2);
    g.drawString("Mundo", 100, 340);

    font3 = new Font("Courier",Font.BOLD+Font.ITALIC,25);
    g.setFont(font3);
    g.drawString("WASAAAA!", 100, 400);

    g.setColor(Color.green);
    g.drawOval(300, 200, 150, 100);
    g.setColor(Color.red);
    g.drawArc(200, 400, 250, 64, 135, 46);
    g.setColor(Color.blue);
    g.drawLine(400, 200, 150, 100);
    g.setColor(Color.magenta);
    g.drawRect(300, 250, 160, 50);
    g.setColor(Color.cyan);
    g.fillRect(100,400,20,240);
    g.setColor(Color.lightGray);
    g.fillOval(100,340,14,30); 

    if(e.getSource() == c){ //Clean all objects on the window//
        g.clearRect(0,100,900,800);
    }
}

public static void main(String args[]){
    miClass GUI = new miClass();
}
}

Answer 1

Your frame is reset to its initial state when it is resized, and your code only redraws it when a button is clicked, not when it is resized. The paintComponent method on any subclass of Component is called after the parent frame is resized, so you can fix this issue by overriding that method.

package SO;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

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

public class miClass implements ActionListener {


  JFrame ventana;
  JPanel panel;
  JButton p, c;
  Graphics g;
  Image img;
  Font font1, font2, font3;

  public miClass() {
    ventana = new JFrame("Aplicacion.");
    p = new JButton("P");
    c = new JButton("C");
    panel = new JPanel() {
      @Override
      public void paintComponent(Graphics g) {
        // your stuff
        font1 = new Font("Helvetica", Font.PLAIN, 22);
        g.setFont(font1);
        g.drawString("THIS GETS REDRAWN", 100, 300);
      }
    };
    panel.setSize(400, 400);
    ventana.setLayout(null);
    ventana.setBounds(100, 100, 600, 600);
    ventana.getContentPane().add(panel);
    ventana.add(p);
    p.addActionListener(this);
    c.addActionListener(this);
    p.setBounds(20, 20, 120, 45);
    ventana.add(c);
    c.setBounds(200, 20, 120, 45);
    ventana.setFocusable(true);
    ventana.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    ventana.setVisible(true);
  }

  public void actionPerformed(ActionEvent e) {
    g = panel.getGraphics();
    Toolkit tool = Toolkit.getDefaultToolkit();
    img = tool.getImage("prueba.png");
    g.drawImage(img, 0, 100, null);

    font1 = new Font("Helvetica", Font.PLAIN, 22);
    g.setFont(font1);
    g.drawString("Hola", 100, 300);

    font2 = new Font("TimesRoman", Font.BOLD, 20);
    g.setFont(font2);
    g.drawString("Mundo", 100, 340);

    font3 = new Font("Courier", Font.BOLD + Font.ITALIC, 25);
    g.setFont(font3);
    g.drawString("WASAAAA!", 100, 400);

    g.setColor(Color.green);
    g.drawOval(300, 200, 150, 100);
    g.setColor(Color.red);
    g.drawArc(200, 400, 250, 64, 135, 46);
    g.setColor(Color.blue);
    g.drawLine(400, 200, 150, 100);
    g.setColor(Color.magenta);
    g.drawRect(300, 250, 160, 50);
    g.setColor(Color.cyan);
    g.fillRect(100, 400, 20, 240);
    g.setColor(Color.lightGray);
    g.fillOval(100, 340, 14, 30);

    if (e.getSource() == c) { // Clean all objects on the window//
      g.clearRect(0, 100, 900, 800);
    }
  }

  public static void main(String args[]) {
    miClass GUI = new miClass();
  }



}