使用IntelliJ IDEA GUI Designer在$$$ setupUI $$$上的NullPointer异常

Question

我一直在尝试在我正在使用的applet中使用我在IntelliJ IDEAS GUI Designer中创建的GUI.当我在我的根JPanel中只有一个标签但是由于某种原因当我添加更多组件时,我得到了运行的东西我得到以下错误:

java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:1095)
at java.awt.Container.add(Container.java:971)
at inputGui.$$$setupUI$$$(inputGui.java)
at inputGui.<init>(inputGui.java:25)
at HelloWorld.init(HelloWorld.java:11)
at sun.applet.AppletPanel.run(AppletPanel.java:435)
at java.lang.Thread.run(Thread.java:745)

我的GUI类inputGui.java是这样的:

(我将标记它打破的行://!BROKEN - 第25行!)

public class inputGui extends JFrame {
private JPanel rootNode;
private JTextField id_field;
private JTextField mi_field;
private JTextField lastName_field;
private JTextField address_field;
//more declorations...

public inputGui() {//initialize GUI
        super( "Hello World" );
        setContentPane( rootNode );//!BROKEN - Line 25!
        pack();
        setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        setVisible( false );
    }
    public JPanel getRootNode() {
        return rootNode;
    }
    private void createUIComponents() {
        // TODO: place custom component creation code here
    }
}

我从我的Applets的init()函数中调用它:

public class HelloWorld extends JApplet {
    //Called when this applet is loaded into the browser.
    public void init() {
        //Execute a job on the event-dispatching thread; creating this applet's GUI.
        inputGui frame =  new inputGui();//just here to get a clearer error
        try {
            SwingUtilities.invokeAndWait(new Runnable() {
                public void run() {
                    Container content = getContentPane();
                    inputGui frame =  new inputGui();//init GUI
                    content.add(frame.getRootNode() );//add rootNode to JFRame

                }
            });
        } catch (Exception e) {
            System.err.println("createGUI didn't complete successfully");
        }
    }

}

我只是想不通为什么添加组件突然创建一个空指针!如果有任何帮助我的元素嵌套如下:

Answer 1

inputGui.java中的代码

private void createUIComponents() {
   // TODO: place custom component creation code here
}

您在UI设计器中的某个组件上选择了"自定义创建"选项.您应该自己创建该组件,否则它将失败.取消选中该选项,一切都应该没问题.