java - 如何将按钮添加到特定的 JPanel 中

Question

我有一个大面板。 bigPanel 内部有多个面板(panel_1、panel_2、panel_3 等......)

bigPanel 使用 GridBagLayout。 panel_1等使用GridLayout。

在另一个面板中，我创建了一个“添加”按钮。如果用户单击此按钮，则会出现一个 JDialog，用户必须填写表单:

1. 按钮名称:
2. 数量:
3. 字母:

用户填写完 JDialog 表单后，将基于 JDialog 表单创建一个新按钮。

此代码将在用户单击 JDialog 表单中的 FINISHED 按钮后执行:

if(Number=="1"){
                    if(Alphabet=="A")
                    {   

                    JButton newButton = new JButton(buttonName);                        
                    //bigPanel.add(newButton);
                    //bigPanel.updateUI();  
                    panel_1.add(newButton);
                    panel_1.updateUI();

                    JOptionPane.showMessageDialog(null,"Successfully added !");
                    }

                    }
                    else if(Alphabet=="B"){
                    JButton newButton = new JButton(buttonName);                        
                    //bigPanel.add(newButton);
                    //bigPanel.updateUI();  
                    panel_2.add(newButton);
                    panel_2.updateUI();

                    JOptionPane.showMessageDialog(null,"Successfully added !");
                    }
                    ...
                }
if (Number=="2"){
                    ...
                    }
                 ...

我用数字 1 和字母 A 测试 JDialog。目前我得到的结果是控制台中的警告，表明此行有问题:

panel_1.add(newButton);//line 313

控制台中的警告:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at UI2$3.actionPerformed(UI2.java:313)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

未添加按钮。但如果我改成

bigPanel.add(newButton);
bigPanel.updateUI();

newButton 已添加到 bigPanel 中。不幸的是，我希望将 newButton 添加到 panel_1 而不是 bigPanel 中。

Answer 1

请检查是否添加了panel_1