如何解决我在 MyPanel 类中创建和显示面板时遇到问题
我正在使用 Java Swing 进行 Uni 项目。我想创建一个包含温度和其他变量的统计面板。
我在 MyPanel 类中创建和显示面板时遇到问题。
当我将类 Main 中的 MyPanel p = new MyPanel() 替换为类 paintComponent 中方法 MyPanel 的内容时，它可以工作，但反过来不行。我想在一个单独的类中创建面板，然后调用它。
public class Main extends JFrame {
public static void main(String[] args) {
SwingUtilities.invokelater(new Runnable() {
public void run() {
JPanel p = createAndShowGUI();
}
});
}
private static JPanel createAndShowGUI() {
System.out.println("Created GUI on EDT? "+
SwingUtilities.isEventdispatchThread());
JFrame f = new JFrame("Swing Demo");
f.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
MyPanel p = new MyPanel();
f.add(p);
//f.add(new MyPanel());
f.pack();
f.setVisible(true);
return p;
}
}
public class MyPanel extends JPanel {
private JLabel TemperaturLabel ;
private JTextField Temperatur ;
private JLabel LuftfeuchtigkeitLabel;
private JTextField Luftfeuchtigkeit;
private JLabel luftdruckLabel;
private JTextField luftdruck;
private JLabel VorhersageLabel;
private JPanel Panel;
protected void paintComponent(Graphics g) {
TemperaturLabel = new JLabel("Temperatur: ");
Temperatur = new JTextField(2);
LuftfeuchtigkeitLabel = new JLabel("Luftfeuchtigkeit: ");
Luftfeuchtigkeit = new JTextField(3);
luftdruckLabel = new JLabel("Luftdruck: ");
luftdruck = new JTextField(4);
Panel= new JPanel( new GridBagLayout());
VorhersageLabel = new JLabel("Vorhersage:------");
GridBagConstraints c = new GridBagConstraints();
c.insets= new Insets(10,10,10);
c.gridx=0;
c.gridy=1;
Panel.add(TemperaturLabel,c);
c.gridx=1;
c.gridy=1;
Panel.add(Temperatur,c);
c.gridx=0;
c.gridy=2;
Panel.add(LuftfeuchtigkeitLabel,c);
c.gridx=1;
c.gridy=2;
Panel.add(Luftfeuchtigkeit,c);
c.gridx=0;
c.gridy=3;
Panel.add(luftdruckLabel,c);
c.gridx=1;
c.gridy=3;
Panel.add(luftdruck,c);
c.gridx=0;
c.gridy=4;
Panel.add(VorhersageLabel,c);
c.gridx=1;
c.gridy=4;
}
public Dimension getPreferredSize() {
return new Dimension(900,700);
}
}
解决方法
所以你期待看到这样的东西？
该代码中有许多逻辑错误导致了许多问题。这是更正后的代码，其中大部分都带有注释。 （有些没有固定，因为它们最终没有太大区别。）
根本问题来自扩展和创建 JPanel 的实例。最终出现在框架中的是未添加任何内容的扩展面板！
import java.awt.*;
import javax.swing.*;
// Use meaningful names for classes,attributes and methods!
// Don't. Extend. JFrame!
// public class Main extends JFrame {
public class MyPanelDisplayProblem {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
// See comments below
// JPanel p = createAndShowGUI();
createAndShowGUI();
}
});
}
// why is this method returning anything? It makes no sense to do that.
// private static JPanel createAndShowGUI() {
private static void createAndShowGUI() {
System.out.println("Created GUI on EDT? "
+ SwingUtilities.isEventDispatchThread());
JFrame f = new JFrame("Swing Demo");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Oh my! This clashes with another name in my 'junk code' package!
// Again. Descriptive names!
// MyPanel p = new MyPanel();
WeatherPanel p = new WeatherPanel();
f.add(p.getPanel());
//f.add(new MyPanel());
f.pack();
f.setVisible(true);
}
}
/* Don't extend panels either,unless custom painting. */
//class WeatherPanel extends JPanel {
class WeatherPanel {
/*
* Please learn common Java nomenclature (naming conventions - e.g.
`EachWordUpperCaseClass`,`firstWordLowerCaseMethod()`,`firstWordLowerCaseAttribute` unless it is an `UPPER_CASE_CONSTANT`)
and use it consistently.
*/
private JLabel TemperaturLabel ;
private JTextField Temperatur ;
private JLabel LuftfeuchtigkeitLabel;
private JTextField Luftfeuchtigkeit;
private JLabel luftdruckLabel;
private JTextField luftdruck;
private JLabel VorhersageLabel;
private JPanel Panel;
/*
The resoning here is entirely wrong. Components should be created and
added from within a constructor!
*/
// protected void paintComponent(Graphics g) {
public WeatherPanel() {
TemperaturLabel = new JLabel("Temperatur: ");
Temperatur = new JTextField(2);
LuftfeuchtigkeitLabel = new JLabel("Luftfeuchtigkeit: ");
Luftfeuchtigkeit = new JTextField(3);
luftdruckLabel = new JLabel("Luftdruck: ");
luftdruck = new JTextField(4);
Panel= new JPanel( new GridBagLayout());
VorhersageLabel = new JLabel("Vorhersage:------");
GridBagConstraints c = new GridBagConstraints();
c.insets= new Insets(10,10,10);
c.gridx=0;
c.gridy=1;
Panel.add(TemperaturLabel,c);
c.gridx=1;
c.gridy=1;
Panel.add(Temperatur,c);
c.gridx=0;
c.gridy=2;
Panel.add(LuftfeuchtigkeitLabel,c);
c.gridx=1;
c.gridy=2;
Panel.add(Luftfeuchtigkeit,c);
c.gridx=0;
c.gridy=3;
Panel.add(luftdruckLabel,c);
c.gridx=1;
c.gridy=3;
Panel.add(luftdruck,c);
c.gridx=0;
c.gridy=4;
Panel.add(VorhersageLabel,c);
c.gridx=1;
c.gridy=4;
}
// Now to get the panel that is created,we can add a 'get panel' method.
public JPanel getPanel() {
return Panel;
}
/**
* This is both unnecessary and counterproductive.
* See [Should I avoid the use of set(Preferred|Maximum|Minimum)Size
* methods in Java Swing?](http://stackoverflow.com/q/7229226/418556)
* (Yes.)
*/
/*
public Dimension getPreferredSize() {
return new Dimension(900,700);
}
*/
}
我拿走了你的代码，重新排列了它，并添加了一些东西来获得这个 GUI。
我重新编写了您的 createAndShowGUI 方法以删除静态并使用我创建的新 getPanel 方法。
我重新编写了您的 TemperaturePanel 类以创建并显示一个 JPanel。我按列、行顺序组织您的 Swing 组件，以便我可以直观地验证 Swing 组件。我添加了缺失的 JTextField。我创建了 getter 方法，因此您可以实际获取和设置 JTextFields 中的值。
我格式化了代码并使用了正确的驼峰式变量名。
这是修改后的代码。我将 TemperaturePanel 设为内部类，以便我可以将此代码作为一个块发布。
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class TemperatureGUI {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
new TemperatureGUI().createAndShowGUI();
}
});
}
private void createAndShowGUI() {
System.out.println("Created GUI on EDT? " +
SwingUtilities.isEventDispatchThread());
JFrame f = new JFrame("Swing Demo");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
TemperaturePanel p = new TemperaturePanel();
f.add(p.getPanel());
// f.add(new MyPanel());
f.pack();
f.setLocationByPlatform(true);
f.setVisible(true);
}
public class TemperaturePanel {
private JTextField temperatur;
private JTextField luftfeuchtigkeit;
private JTextField luftdruck;
private JTextField vorhersage;
private JPanel panel;
public TemperaturePanel() {
this.panel = createAndShowPanel();
}
private JPanel createAndShowPanel() {
JPanel panel = new JPanel(new GridBagLayout());
panel.setBorder(BorderFactory.createEmptyBorder(5,5,5));
GridBagConstraints c = new GridBagConstraints();
c.anchor = GridBagConstraints.LINE_START;
c.fill = GridBagConstraints.HORIZONTAL;
c.weightx = 1.0;
c.insets = new Insets(10,10);
c.gridx = 0;
c.gridy = 1;
JLabel temperaturLabel = new JLabel("Temperatur: ");
panel.add(temperaturLabel,c);
c.gridx = 1;
c.gridy = 1;
temperatur = new JTextField(10);
panel.add(temperatur,c);
c.gridx = 0;
c.gridy = 2;
JLabel luftfeuchtigkeitLabel = new JLabel("Luftfeuchtigkeit: ");
panel.add(luftfeuchtigkeitLabel,c);
c.gridx = 1;
c.gridy = 2;
luftfeuchtigkeit = new JTextField(10);
panel.add(luftfeuchtigkeit,c);
c.gridx = 0;
c.gridy = 3;
JLabel luftdruckLabel = new JLabel("Luftdruck: ");
panel.add(luftdruckLabel,c);
c.gridx = 1;
c.gridy = 3;
luftdruck = new JTextField(10);
panel.add(luftdruck,c);
c.gridx = 0;
c.gridy = 4;
JLabel vorhersageLabel = new JLabel("Vorhersage:------");
panel.add(vorhersageLabel,c);
c.gridx = 1;
c.gridy = 4;
vorhersage = new JTextField(10);
panel.add(vorhersage,c);
return panel;
}
public JTextField getTemperatur() {
return temperatur;
}
public JTextField getLuftfeuchtigkeit() {
return luftfeuchtigkeit;
}
public JTextField getLuftdruck() {
return luftdruck;
}
public JTextField getVorhersage() {
return vorhersage;
}
public JPanel getPanel() {
return panel;
}
}
}
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