java 在 JScrollPane 中使用绝对布局

Use a absolute layout inside a JScrollPane

提问by Jonás

I need to use a JScrollPane with absolute layoute. I know that the use of setLayout(null) is not recommendable at all. I've been reading that if you want to use the absolute layout with a JScrollPane it is necessary to set the preferred size property of the elements inside in order to JScrollPane can calculate its size.

我需要使用具有绝对布局的 JScrollPane。我知道 setLayout(null) 的使用根本不值得推荐。我一直在读，如果你想在 JScrollPane 中使用绝对布局，则必须设置内部元素的首选大小属性，以便 JScrollPane 可以计算其大小。

I've been trying the next code changing the order and sizes of elemnts but I can't work out where I've been wrong.

我一直在尝试更改元素的顺序和大小的下一个代码，但我无法弄清楚我错在哪里。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;


public class frame extends JFrame {

private JPanel contentPane;
private JScrollPane scrollPane;

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                frame frame = new frame();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

public frame() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 450, 300);
    contentPane = new JPanel();
    contentPane.setLayout(null);
    setContentPane(contentPane);

    JPanel panel = new JPanel();
    panel.setBackground(Color.red);
    panel.setBounds(0,0,600,600);
    panel.setPreferredSize(new Dimension(420,280));

    scrollPane = new JScrollPane(panel);
    scrollPane.setBounds(0, 0, 600, 600);
    scrollPane.setLayout(null);
    scrollPane.setBackground(Color.green);

    scrollPane.add(panel);
    scrollPane.setPreferredSize(new Dimension(450,300));
    contentPane.add(scrollPane);
}
}

Why setPreferredSize is not doing the right work? Thanks in advance.

为什么 setPreferredSize 没有做正确的工作？提前致谢。

采纳答案by Adamski

Changing the layout manager of the actual JScrollPanedoes not make sense; if you wish to use absolute layout within your application you would typically call setLayout(null)on a container class (such as JPanel) in order to position child components within it using absolute positioning.

更改实际的布局管理器JScrollPane没有意义；如果您希望在应用程序中使用绝对布局，您通常会调用setLayout(null)容器类（例如JPanel），以便使用绝对定位将子组件定位在其中。

I suggest that you should try:

我建议你应该尝试：

• Call setLayout(null)on the JPanelcontained within the JScrollPane(as I thinkthis is what you're trying to do).
• Rather than use JPaneldirectly, subclass it and have your subclass implement the Scrollableinterface, which provides additional information to the JScrollPaneregarding the optimal scrollable viewport size.

• 呼叫setLayout(null)在JPanel其中所包含的JScrollPane（因为我认为这是你想要做什么）。
• 与其JPanel直接使用，不如将其子类化并让您的子类实现Scrollable接口，这为JScrollPane有关最佳可滚动视口大小提供了额外的信息。

回答by MadProgrammer

First of all, don't change the layout manager of the scroll pane, it's not required for what you want to achieve

首先，不要更改滚动窗格的布局管理器，它不是您想要实现的必需的

Second, scroll pane works though a JViewport. You have to add your container to it instead (scrollPane.add(panel)is the wrong thing to do), instead use scrollPane.setViewportView(panel)

其次，滚动窗格通过JViewport. 您必须将容器添加到其中（这scrollPane.add(panel)是错误的做法），而是使用scrollPane.setViewportView(panel)

Thirdly, you want to take a look at the Scrollableinterface as scroll pane doesn't just rely on the preferred size of its contents

第三，您想看看Scrollable界面，因为滚动窗格不仅仅依赖于其内容的首选大小

回答by Nievinski

I can see your problem.

我可以看到你的问题。

Here you set the bound and the preferred size of your panel.

您可以在此处设置面板的边界和首选大小。

panel.setBounds(0,0,600,600);
panel.setPreferredSize(new Dimension(420,280));

then you set the bound of the scrollPane

然后你设置滚动窗格的边界

scrollPane.setBounds(0, 0, 600, 600);

Well, the bounds of the panel is useless, cause scrollPane cares only about the preferred size, and the preferred size of the panel is smaller then the bounds of the scrollPane, so the scrollPanel thinks he doesn't need to show anything else, that's why it doesn't show any scrollBars or enable them. OBS: I see no sense at setting the layout of the scrollPanel. So you can skip that line.

好吧，面板的边界没用，因为scrollPane只关心首选大小，而面板的首选大小比scrollPane的边界小，所以scrollPanel认为他不需要显示任何其他东西，那就是为什么它不显示任何滚动条或启用它们。OBS：我认为设置 scrollPanel 的布局没有意义。所以你可以跳过那一行。

Just as commentary: Using scroll with absolut layout pane is just fine since you make the care of the preferred size of the pane.

就像评论一样：使用带有绝对布局窗格的滚动就可以了，因为您可以关注窗格的首选大小。