Question

目前，我有一个嵌套在具有BorderLayout的Panel中的JScrollPane。更重要的是，在JScrollPane中，我打算垂直列出多个文本区域，其宽度不超过JScrollPane，并且需要尽可能多的高度（滚动窗格只有一个垂直滚动条）。

我的问题是文本区域看起来相对于最大的文本区域在JScrollPane中居中，并且它们都是一行。

任何人都可以告诉我，查看我的代码，如何在滚动窗格的右侧之前将文本区域包裹起来，以及如何将它们保持对齐？

private JPanel generateStateView(State state) {
        //Create a new panel, and the info label.
        JPanel container = new JPanel(new BorderLayout());
        JLabel infoLabel = new JLabel("The state of " + state.getName() + 
                ", with " + state.getElectoralVotes() + " Electoral Votes.");
        container.add(infoLabel, BorderLayout.NORTH); //Put the label on top.
        //Will scroll through polls.
        JScrollPane pollViewer = new JScrollPane();
        //This will be the scroll pane's "viewport".
        JViewport pollViewport = new JViewport();
        //And finally, this will actually hold the individual polls.
        JPanel pollPanel = new JPanel(new GridLayout(
                state.getPolls().size(), 1));
        pollPanel.setAlignmentX(LEFT_ALIGNMENT);
        //Iteratively add the polls to the container
        for (Poll poll : state.getPolls()) {
            //Holds individual polls
            Box pollBox = Box.createHorizontalBox();
            //Create the poll's panel and add it to the poll container.
            pollBox.add(generatePollPanel(poll));
            pollBox.add(Box.createHorizontalGlue()); //Fill to the right
            pollBox.setAlignmentX(LEFT_ALIGNMENT);
            pollPanel.add(pollBox); //Put the box into the pollPanel.
        }
        //Put the panel into the viewport.
        pollViewport.add(pollPanel);
        //Put the viewport "into" the scroll pane
        pollViewer.setViewport(pollViewport);
        //Put the pane into the state view.
        container.add(pollViewer, BorderLayout.CENTER);
        return container; //And give back the container.
    }

    /**
     * Method: generatePollPanel
     * Purpose: Generates a panel containing information on a particular poll.
     * @param poll The poll to have information generated from.
     * @return The JPanel.
     */
    private JPanel generatePollPanel(Poll poll) {
        //Create a new panel, then a text area to fill with the info.
        JPanel pollPanel = new JPanel();
        JTextArea pollInfo = new JTextArea("Conducted by " + poll.getAgency() + 
                " on day " + poll.getDate() + " for " + poll.getNumDays() + 
                " days, " + poll.getPercentVoteDem() +
                "% voted Democrat, and " + poll.getPercentVoteRep() +
                "% voted Republican.");
        pollInfo.setEditable(false); //We don't want the user editing this.
        pollPanel.add(pollInfo); //Throw the area in, and return the panel.
        pollPanel.setAlignmentX(LEFT_ALIGNMENT);
        return pollPanel;
    }

    /**
     * Method: valueChanged
     * Purpose: Handle the event of a different list item being selected.
     * @param event The object containing information about this event.
     */
    public void valueChanged(ListSelectionEvent event) {
        //Instantiating JList with a type of ? seems to solve the issue of
        //eclipse complaining about an unchecked cast (originally to
        //JList<String>, so I should be able to cast child values directly
        //to string later on anyways.
        JList<?> stateList = (JList<?>) event.getSource();
        //Account for keyboard and mouse actions
        if (!event.getValueIsAdjusting()) {
            State chosenState; //Keep track of the picked state.
            try {
                //Try to get the currently selected state
                chosenState = db.findState((String) stateList.getSelectedValue());
            }
            catch (NoSuchElementException exception) {
                //Somehow the picked state was not found, notify the user.
                reportError("The selected state is not available.");
                return;
            }
            //Find the container for the gui window.
            Container container = getContentPane();
            //Remove the empty state view container by generating a new one.
            container.remove(currentStateView);
            //Generate the state view and add that to the container.
            currentStateView = generateStateView(chosenState);
            container.add(currentStateView, BorderLayout.CENTER);
            //Redraw everything.
            revalidate();
        }
    }

Answer 1

看起来像遗失了的严重情况： - ）

虽然嵌套可以是实现布局要求的一种方法，但如果不能提供预期的输出，很难找出究竟出现了什么问题。此外，还有一些警告信号表明嵌套基本上是错误的

深层次的容器管理员差异很大
只有一个孩子的容器

在您的情况下，除了顶级borderlayout之外的所有内容都有一个“netto”（也就是说，不打算围绕布局问题）孩子，其级别为：

BorderLayout (the state view)
   GridLayout (the panel that's the scrollPane's view)
      BoxLayout (the panel that contains a single pollBox)
         FlowLayout (the panel that contains the textArea)

经验丰富的问题：

文本区域是单行而不包装
文本区域居中

都归功于LayoutManagers的特性，无论是部分（第一）还是完全（第二）：

未归属于管理器的部分是textArea默认不包装，您必须明确配置它才能这样做。由管理者（== FlowLayout）引起的部分是总是根据他们的prefSize布置其子项，没有别的。无论父母有多少空间，这都归结为具有固定的子尺寸。因此，即使textArea配置为wrap，它也会坚持初始大小，无论它的父级有多宽。
内部FlowLayout将其子项对齐...居中。因此，您在BoxLayout级别设置的任何对齐都没有任何效果。不像胶水一样：如果另一个子/ ren在该维度中具有最大大小（具有FlowLayout的面板没有，只是因为它就是那么简单的LayoutManager），它只需要所有多余的空间没有max的概念，只有LayoutManager2类型的管理器有）

时间退后一步并审查初始要求：

垂直列出的多个文本区域，宽度不是超过JScrollPane，以及他们需要的高度

零订单解决方案是

根据需要配置textArea
抛弃所有布局嵌套（在scrollPane内）

在代码中：

JComponent overview = new JPanel(new BorderLayout());
overview.add(new JLabel("All polls for state XY"), BorderLayout.NORTH);

JComponent pollPanel = new JPanel(); 
pollPanel.setLayout(new BoxLayout(pollPanel, BoxLayout.PAGE_AXIS));
for (int i = 0; i < 10; i++) {
    pollPanel.add(generatePollTextArea(i)); //Put the box into the pollPanel.
}
pollPanel.add(Box.createVerticalGlue());
JScrollPane pollViewer = new JScrollPane(pollPanel);
overview.add(pollViewer);
showInFrame(overview, "layout text only");

protected JComponent generatePollTextArea(int i) {
    String agency = "agency ";
    // simulates different size text
    for (int j = 0; j < i; j++) {
        agency += i;
    }
    String text = "Conducted by " + agency + 
            " on day " + "today" + " for " + 20 + 
            " days, " + 99 +
            "% voted Democrat, and " + 0.2 +
            "% voted Republican.";
    JTextArea pollInfo = new JTextArea(text); 
    // give it some reasonable initial width
    // in terms of content
    pollInfo.setColumns(20);
    pollInfo.setLineWrap(true);
    pollInfo.setWrapStyleWord(true);
    pollInfo.setEditable(false); //We don't want the user editing this.
    return pollInfo;
}

“Das Wort zum Dienstag”：嵌套布局不是避免学习在嵌套布局的各个级别上使用的LayoutManagers的特征的手段。

Answer 2

首先，我不认为Box被认为与BoxLayout以外的任何东西一起使用（我可能错了，但这就是我读它的方式）

就个人而言，我要么使用SwingLabs的GridBagLayout或VerticalLayout。

为了便于横向限制，您还需要查看Scrollable界面，尤其是getScrollableTracksViewportWidth

将JScrollPane的组件对齐到左侧？

2 个答案: