BorderLayout-添加另一个组件后，子组件仍然可见 [英] BorderLayout - child component remains visible after adding another component

问题描述

我尝试执行以下操作:

1. 使用BorderLayout
将组件添加到JFrame
2. 将另一个组件添加到JFrame

由于我使用的是BorderLayout，因此我希望新组件覆盖"旧组件.如果在调用pack()之前覆盖了旧组件，则可以使用此功能.现在，如果我在之后添加第二个组件，则调用pack()，这两个组件都保持可见.示例:

I would expect the new component to 'overwrite' the old component, since I'm using a BorderLayout. This works if I overwrite the old component before I call pack(). Now if I add the 2nd component after I call pack(), both components remain visible. Example:

public class Test extends JFrame{
    public Test(){
        setLayout(new BorderLayout());
        add(new JLabel("Quite a long text"));
        setVisible(true);
        pack();
        add(new JLabel("Another text"));
    }
}

结果:

public class Test extends JFrame{
    public Test(){
        setLayout(new BorderLayout());
        add(new JLabel("Quite a long text"));
        setVisible(true);
        add(new JLabel("Another text"));
        pack();
    }
}

结果:

我尝试添加validate();和repaint();，但这无济于事.这是怎么了

I tried adding validate(); and repaint();, but that wouldn't help. What's going wrong here?

推荐答案

在调用setViisble()之后，您正在调用会影响UI的事物-Swing不行.将影响用户界面的内容放入invokeLater调用中；查找它.

You are calling things that affect the UI after setViisble() is called -- a Swing no-no. Put things that affect the UI into an invokeLater call; look it up.

在使用它时，我认为您仍然应该从框架中获取内容窗格以添加组件...而且我认为在构造函数中创建东西不是一个好主意.

While you're at it, I think you're still supposed to get the content pane from the frame for adding components... And I don't think creating things in the constructor is a good idea.

import java.awt.BorderLayout;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;

public class SwingTest extends JFrame
{
    public void createUI()
    {
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
        SwingUtilities.invokeLater(
                new Runnable()
                {
                    public void run()
                    {
                        getContentPane().setLayout(new BorderLayout());
                        getContentPane().add(new JLabel("Quite a long text"), BorderLayout.CENTER);
                        getContentPane().add(new JLabel("Another text"), BorderLayout.CENTER);
                        pack();
                        setVisible(true);
                    }
                }
                );
    }

    public static void main(String ... args) 
    { 
        SwingTest st = new SwingTest();
        st.createUI();
    }
}

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