在分配新变量(setter)并调用repaint()后无法更改paintComponent的输出

Question

我被困在同一个地方将近1天，我仍然找不到我的代码错误在哪里。需要你们帮忙，这是我的密码。(相当长)

My JFrame class:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class CircleProject extends JFrame implements ActionListener{
JTextField xTextField1;
JTextField yTextField1;
JTextField textFieldRadiusLeft;
JTextField xTextField2;
JTextField yTextField2;
JTextField textFieldRadiusRight;
JButton redraw;
public static void main(String[] args) {
CircleProject frame = new CircleProject();
frame.setResizable(true);
frame.setVisible(true);
frame.setSize(580, 700);
frame.setTitle("YONG JING PING FINAL PROJECT");
}
public CircleProject() {
JPanel titlePanel = new JPanel(new FlowLayout(FlowLayout.CENTER));
JLabel theTitle = new JLabel("Two Circles Intersect?");
JLabel intersection = new JLabel("");
titlePanel.add(theTitle);
titlePanel.add(intersection);
JPanel contentPanel = new JPanel(new GridLayout(2, 1));
JPanel userInputPanel = new JPanel(new FlowLayout(FlowLayout.CENTER));
JPanel gridPanel = new JPanel(new GridLayout(1, 2, 8, 0));
JPanel leftInputPanel = new JPanel(new GridLayout(4, 1));
JLabel inputTitle1 = new JLabel("Enter circle 1 info: ");
inputTitle1.setHorizontalAlignment(JLabel.CENTER);
JPanel xInputPanelLeft = new JPanel();
xTextField1 = new JTextField(5);
xInputPanelLeft.add(new JLabel("Center X: "));
xInputPanelLeft.add(xTextField1);
JPanel yInputPanelLeft = new JPanel();
yTextField1 = new JTextField(5);
yInputPanelLeft.add(new JLabel("Center Y: "));
yInputPanelLeft.add(yTextField1);
JPanel radiusLeft = new JPanel();
textFieldRadiusLeft = new JTextField(5);
radiusLeft.add(new JLabel("Radius: "));
radiusLeft.add(textFieldRadiusLeft);
leftInputPanel.add(inputTitle1);
leftInputPanel.add(xInputPanelLeft);
leftInputPanel.add(yInputPanelLeft);
leftInputPanel.add(radiusLeft);
leftInputPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK));
JPanel rightInputPanel = new JPanel(new GridLayout(4, 1));
JLabel inputTitle2 = new JLabel("Enter circle 2 info: ");
inputTitle2.setHorizontalAlignment(JLabel.CENTER);
JPanel xInputPanelRight = new JPanel();
xTextField2 = new JTextField(5);
xInputPanelRight.add(new JLabel("Center X: "));
xInputPanelRight.add(xTextField2);
JPanel yInputPanelRight = new JPanel();
yTextField2 = new JTextField(5);
yInputPanelRight.add(new JLabel("Center Y: "));
yInputPanelRight.add(yTextField2);
JPanel radiusRight = new JPanel();
textFieldRadiusRight = new JTextField(5);
radiusRight.add(new JLabel("Radius: "));
radiusRight.add(textFieldRadiusRight);
rightInputPanel.add(inputTitle2);
rightInputPanel.add(xInputPanelRight);
rightInputPanel.add(yInputPanelRight);
rightInputPanel.add(radiusRight);
rightInputPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK));
gridPanel.add(leftInputPanel);
gridPanel.add(rightInputPanel);
userInputPanel.add(gridPanel);
contentPanel.add(new DrawPanel());
contentPanel.add(userInputPanel);
redraw = new JButton("Redraw Circles");
redraw.setEnabled(true);
redraw.addActionListener(this);
JPanel buttonPanel = new JPanel();
buttonPanel.add(redraw);
setLayout(new BorderLayout());
add(titlePanel, BorderLayout.NORTH);
add(contentPanel, BorderLayout.CENTER);
add(buttonPanel, BorderLayout.SOUTH);
}
DrawPanel drawCircle = new DrawPanel();
@Override
public void actionPerformed(ActionEvent e) {
this.setVisible(false);
if (e.getSource() == redraw) {
CircleProject frame2 = new CircleProject();
frame2.setResizable(false);
frame2.setVisible(true);
frame2.setSize(580,700);
frame2.setTitle("YONG JING PING FINAL PROJECT");

String text = xTextField1.getText();
int x1 = Integer.parseInt(text);
String text1 = xTextField2.getText();
int x2 = Integer.parseInt(text1);
String text2 = yTextField1.getText();
int y1 = Integer.parseInt(text2);
String text3 = yTextField2.getText();
int y2 = Integer.parseInt(text3);
String text4 = textFieldRadiusLeft.getText();
int r1 = Integer.parseInt(text4);
String text5 = textFieldRadiusRight.getText();
int r2 = Integer.parseInt(text5);
drawCircle.setCenterColumn1(x1, y1, r1);
drawCircle.setCenterColumn2(x2, y2, r2);
}
}
}

我的Drawpanel类:

import javax.swing.*;
import java.awt.*;
public class DrawPanel extends JPanel{
//    the coordinate's variables is the start point of it.
int coordinateX1=50, coordinateX2=300, coordinateY1=50, coordinateY2=50, radius1=0, radius2=0, length1=200, length2=200;
public void setCenterColumn1(int x, int y, int radius1){
this.coordinateX1 = x-radius1;
this.coordinateY1 = y-radius1;
this.radius1 = radius1;
length1 = radius1*2;
System.out.println(coordinateX1);
System.out.println(coordinateY1);
System.out.println(length1);
System.out.println(coordinateX2);
System.out.println(coordinateY2);
System.out.println(length2);
System.out.println("-------1-------");
repaint();
}
public void setCenterColumn2(int x, int y, int radius2){
this.coordinateX2=x-radius2;
this.coordinateY2=y-radius2;
this.radius2=radius2;
length2 = radius2*2;
System.out.println(coordinateX1);
System.out.println(coordinateY1);
System.out.println(length1);
System.out.println(coordinateX2);
System.out.println(coordinateY2);
System.out.println(length2);
System.out.println("-------2-------");
repaint();
}
public DrawPanel(){
setBackground(Color.WHITE);
}
//    error from here, when redraw pressed this paintComponent does not
//    show up the new circle.
@Override
public void paintComponent (Graphics g){
super.paintComponent(g);
g.setColor(Color.BLACK);
//        Circle for column 1
g.drawOval(coordinateX1,coordinateY1,length1,length1);
//        Circle for column 2
g.drawOval(coordinateX2,coordinateY2,length2,length2);
System.out.println(coordinateX1);
System.out.println(coordinateY1);
System.out.println(length1);
System.out.println(coordinateX2);
System.out.println(coordinateY2);
System.out.println(length2);
System.out.println("-------3-------");
}
}

我期望的结果是用户输入圆的中心坐标，点击重绘btn后，圆就会被改变。

Answer 1

问题是你没有使用你的变量drawCircle(行:DrawPanel drawCircle = new DrawPanel();)

当你使用insideactionPerformed方法时，你永远不会使用那个变量，因为它创建了Circle Project的另一个实例。(line: CircleProject frame2 = new CircleProject();)

drawCircle变量来自当前正在运行的类，因此，当您再次实例化CircleProject时，该变量内部的更改将不会产生影响。

要解决这个问题，不需要再次实例化，只需要使用该变量。

您必须在构造函数CircleProject()中做的第一件事:

....
userInputPanel.add(gridPanel);
contentPanel.add(drawCircle);
contentPanel.add(userInputPanel);
....

这里的变化只有一个，因为你有contentPanel.add(new DrawPanel());，这是不正确的(正如我所说的，你从来没有使用变量drawCircle)，所以，相反，你必须为contentPanel.add(drawCircle);更改它

另一方面，为了避免实例化CircleProject，您必须删除actionPerformed方法中的一些行，例如:

@Override
public void actionPerformed(ActionEvent e) {
if (e.getSource() == redraw) {

String text = xTextField1.getText();
int x1 = Integer.parseInt(text);
String text1 = xTextField2.getText();
int x2 = Integer.parseInt(text1);
String text2 = yTextField1.getText();
int y1 = Integer.parseInt(text2);
String text3 = yTextField2.getText();
int y2 = Integer.parseInt(text3);
String text4 = textFieldRadiusLeft.getText();
int r1 = Integer.parseInt(text4);
String text5 = textFieldRadiusRight.getText();
int r2 = Integer.parseInt(text5);
drawCircle.setCenterColumn1(x1, y1, r1);
drawCircle.setCenterColumn2(x2, y2, r2);
}
}

我试过这个程序，它对我很有效!我希望这也适用于你:D