Java JPanel 未显示在我的 JFrame 中
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/18872287/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
JPanel is not displaying in my JFrame
提问by Michael Nana
so I'm playing with JPanels and JFrames and I'm noticing that the JPanel I created is not showing displaying when I add it to a Jframe object. Note, that when I created a JPanel in my Jframe constructor giving the jpanel parameters before being added to the Jframe, it worked. However now I'm using a JPanel object I created and it's not working anymore. This is what I have done.
所以我在玩 JPanels 和 JFrames，我注意到当我将它添加到 Jframe 对象时，我创建的 JPanel 没有显示。请注意，当我在我的 Jframe 构造函数中创建一个 JPanel 时，在添加到 Jframe 之前给出 jpanel 参数，它起作用了。但是现在我正在使用我创建的 JPanel 对象，它不再工作了。这就是我所做的。
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class MyGui extends JFrame {
MyMouseListener listen = new MyMouseListener();
public MyGui() {
setSize(500, 500);
//setLayout(new BoxLayout(this, BoxLayout.X_AXIS));
getContentPane().setBackground(Color.WHITE);
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
Panel panel = new Panel();
add(panel, BorderLayout.WEST);
//setVisible(true);
show();
}
public static void main(String[] a) {
MyGui gui = new MyGui();
}
}
class Panel extends JPanel {
MyMouseListener listen = new MyMouseListener();
public Panel() {
setPreferredSize(new Dimension(300, 300));
addMouseListener(listen);
setBackground(Color.YELLOW);
setLayout(new GridLayout(3, 1));
}
public void paint(Graphics g) {
super.paintComponents(g);
g.drawOval((int) Math.round(listen.p.getX()),
(int) Math.round(listen.p.getX()), 1, 1);
}
}
class MyMouseListener implements MouseListener {
Point p = new Point();
@Override
public void mouseClicked(MouseEvent e) {
System.out.println("Mouse was clicked");
}
@Override
public void mousePressed(MouseEvent e) {
p = e.getPoint();
System.out.println(p);
}
@Override
public void mouseReleased(MouseEvent e) {
}
@Override
public void mouseEntered(MouseEvent e) {
}
@Override
public void mouseExited(MouseEvent e) {
}
}
EDIT: Actually I think I've found the error. The JPanel has it's paint method which when deleted allows the Jframe to show the panel. However I need to be able to draw stuff on the JPanel.
编辑：其实我想我已经找到了错误。JPanel 有它的绘制方法，删除时允许 Jframe 显示面板。但是我需要能够在 JPanel 上绘制东西。
采纳答案by Insane Coder
its
它的
super.paintComponent(g);
super.paintComponent(g);
Advice:
建议：
1)You are making things unnecessarily complex. e.g to close the window you should use
1）你让事情变得不必要地复杂。例如关闭你应该使用的窗口
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
instead of the call to System.exit(0);and using window listeners
而不是调用System.exit(0);和使用窗口侦听器
2)As said by @mKorbel , you should use SwingUtilities.invokeLaterto start your gui as Java GUIs are supposed to run on EDT(Event Dispatch Thread) and should not run on main thread.
2）正如@mKorbel 所说，您应该使用SwingUtilities.invokeLater来启动您的 gui，因为 Java GUI 应该在 EDT（事件调度线程）上运行，而不应该在主线程上运行。
回答by Hugo G.
Did you try to set the layout manager and add the panel to the contentPane instead of the JFrame itself ?
您是否尝试设置布局管理器并将面板添加到 contentPane 而不是 JFrame 本身？
getContentPane().setLayout(new BorderLayout());
getContentPane().add(panel, BorderLayout.WEST);
回答by Antoniossss
Default Layout manager for frame is FlowLayoutnot BorderLayout. Try to setLayout(new BorderLayout())in your MyGuicontructor.
框架的默认布局管理器FlowLayout不是BorderLayout. 尝试setLayout(new BorderLayout())在您的MyGui构造函数中。
回答by Sorontur
you didn't set a Layout to your content pane. try someting like getContentPane.setLayout(new Layout())
您没有为内容窗格设置布局。尝试像getContentPane.setLayout(new Layout())
View the oracle docs for details about layout managers: http://docs.oracle.com/javase/tutorial/uiswing/layout/layoutlist.html
有关布局管理器的详细信息，请查看 oracle 文档：http: //docs.oracle.com/javase/tutorial/uiswing/layout/layoutlist.html
hope this helpgs
希望这有帮助
回答by mKorbel
1) super.paintComponents(g); inside paint()could be
1) super.paintComponents(g); 里面paint()可能是
public void paintComponent(Graphics g) {
super.paintComponent(g);
....
}
2) don't to set any size setSize(500,500); or setPreferredSize(new Dimension(300, 300));, to use pack()and then (uncomment) setVisible(true)for JFrame and to override getPreferredSize()for JPanel
2）不要设置任何尺寸setSize(500,500)；或者setPreferredSize(new Dimension(300, 300));，使用pack()和然后（取消注释）setVisible(true)为JFrame的和重写getPreferredSize()为JPanel
3) MyGui gui=new MyGui();inside public static void main(String []a){, should be wrapped into invokeLater, more see in Oracle tutorial Initial Thread
3) MyGui gui=new MyGui();里面public static void main(String []a){，要包裹进去invokeLater，更见里面Oracle tutorial Initial Thread
