java - 当我尝试使用 Swing 将 Container 对象添加到主 JFrame 对象时，为什么会出现此错误？

Question

我对 Java Swing 应用程序绝对是新手，但遇到以下问题。

我有这个简单的LoginFrame2类:

package com.test.login;

import java.awt.Container;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;

import net.miginfocom.swt.MigLayout;

import org.jdesktop.application.SingleFrameApplication;

public class LoginFrame2 extends SingleFrameApplication {

    public static void main(String[] args) {
        System.out.println("DENTRO: LoginFrame() ---> main()");
        launch(LoginFrame2.class, args);
    }

    @Override
    protected void startup() {
        // TODO Auto-generated method stub
        System.out.println("Inside startup()");

        JFrame mainFrame = this.getMainFrame();         // main JFrame that represents the Windows
        mainFrame.setTitle("XCloud Login");

        Container mainContainer = mainFrame.getContentPane();       // main Container into the main JFrame

        // JPanel creation and settings of the MigLayout on it:
        JPanel externalPanel = new JPanel();
        externalPanel.setLayout(new net.miginfocom.swing.MigLayout("fill"));

        externalPanel.add(new JLabel("Username"));

        mainContainer.add(externalPanel);
        mainFrame.add(mainContainer);


    }

}

正如你所看到的，我正在使用 JDesktop 框架的 SingleFrameApplication 抽象类，它只是为我提供一个主要的 JFrame (这个抽象类还负责组件属性注入(inject)、退出处理以及以适合简单单帧应用程序的方式保存/恢复 session 状态)。

当执行该类时，将执行 startUp() 方法。

如您所见，我执行了以下操作:

1. 我使用 getMainFrame() 方法获取主 Jframe，并将其引用放入 ma​​inFrame 变量

2. 我使用主Container(即mainFrame对象)调用getContentPane()方法

3. 然后，我创建一个名为 externalPanel 的 JPanel 对象，在其中放置一个初始化的 JLabel ，它将显示一个字符串。

4. 最后，我将 JPanel 对象添加到 Container 对象，然后尝试将 Container 添加到主 >JFrame 对象。

问题是，当我执行此类时，我收到以下错误消息:

DENTRO: LoginFrame() ---> main()
Inside startup()
8-nov-2013 12.35.23 org.jdesktop.application.Application$1 run
GRAVE: Application class com.test.login.LoginFrame2 failed to launch
java.lang.IllegalArgumentException: adding container's parent to itself
    at java.awt.Container.checkAddToSelf(Container.java:418)
    at java.awt.Container.addImpl(Container.java:1036)
    at java.awt.Container.add(Container.java:957)
    at javax.swing.JFrame.addImpl(JFrame.java:540)
    at java.awt.Container.add(Container.java:363)
    at com.test.login.LoginFrame2.startup(LoginFrame2.java:38)
    at org.jdesktop.application.Application$1.run(Application.java:187)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:672)
    at java.awt.EventQueue.access$400(EventQueue.java:81)
    at java.awt.EventQueue$2.run(EventQueue.java:633)
    at java.awt.EventQueue$2.run(EventQueue.java:631)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:642)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Exception in thread "AWT-EventQueue-0" java.lang.Error: Application class com.test.login.LoginFrame2 failed to launch
    at org.jdesktop.application.Application$1.run(Application.java:192)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:672)
    at java.awt.EventQueue.access$400(EventQueue.java:81)
    at java.awt.EventQueue$2.run(EventQueue.java:633)
    at java.awt.EventQueue$2.run(EventQueue.java:631)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:642)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
Caused by: java.lang.IllegalArgumentException: adding container's parent to itself
    at java.awt.Container.checkAddToSelf(Container.java:418)
    at java.awt.Container.addImpl(Container.java:1036)
    at java.awt.Container.add(Container.java:957)
    at javax.swing.JFrame.addImpl(JFrame.java:540)
    at java.awt.Container.add(Container.java:363)
    at com.test.login.LoginFrame2.startup(LoginFrame2.java:38)
    at org.jdesktop.application.Application$1.run(Application.java:187)
    ... 14 more

我认为问题在于在其 Jframe 对象中添加了 Container 对象。但为什么？据我所知，Container 对象是包装在 JFrame 内的对象......问题出在哪里？我该如何解决？

Tnx

安德里亚

Answer 1

您正在尝试在此容器中添加容器。问题就出在这里

Container mainContainer = mainFrame.getContentPane();
...
mainFrame.add(mainContainer);

this JFrame mainFrame = this.getMainFrame(); 已经有 ContentPane，您还需要再添加一个。每个 JFrame 有 3 个面板 -> glassPane、contentPane 和 LayerdPane。

尝试在 mainContainer 中添加元素(已包含在 mainFrame 中)。