自定义JComponent大小默认为零吗? [英] Custom JComponent size default to zero?

问题描述

我正在尝试将自定义的可滚动JComponent添加到JFrame.

I'm trying to add a custom scrollable JComponent to a JFrame.

JScrollPane sp = new JScrollPane(hg);
frame.getContentPane().add(sp, BorderLayout.CENTER);

hg是我的自定义组件.

hg is my custom component.

问题是未显示我的自定义组件.但是，如果我这样做:

The problem is that my custom component is not displayed. However, if I do this:

hg.setBounds(0, 0, 800, 600);

然后将显示它.但是我当然不想明确设置大小.我希望它适合框架的中心.

Then it will be displayed. But of course I don't want to set size explicitly. I want it to fit in the center of the frame.

在我的自定义JComponent类中，我重写了getPreferredSize():

In my custom JComponent class, I override getPreferredSize():

private Dimension computePreferredSize() {
    return new Dimension((int) (this.getParent().getSize().width * scale),
            (int) (this.getParent().getSize().height * scale));
}

public Dimension getPreferredSize() {
    Dimension d = computePreferredSize();
    System.out.println("Dimension: " + d); // prints reasonable output: Dimension: java.awt.Dimension[width=1201,height=805]
    return d;
}

但这似乎没有任何效果.即使我直接返回固定尺寸:

But this doesn't seem to have any effect. Even if I return a fixed dimension directly:

public Dimension getPreferredSize() {
    return new Dimension(800, 600);
}

这也不起作用.

我还在我的ComponentUI的paint()方法中添加了println，但是没有打印任何内容，因此我认为出于某种原因未调用paint().我认为原因是我的自定义组件的大小默认为零，并且我不确定如何让其调整自己的大小.

I also added println in my ComponentUI's paint() method, but nothing is printed, so I think for some reason paint() is not called. I think the reason why is that my custom component's size defaults to zero, and I'm not sure how to let it adjust its own size.

所以我的问题是:为什么默认情况下不显示我的JComponent，我应该怎么做才能使其自动适应JFrame的中心?

So my question is: why my JComponent is not displayed by default, and what I should do to make it automatically fit into the center of the JFrame?

谢谢！

推荐答案

在定义hg的类中，重写getPreferredSize()以返回组件的首选大小.可以在此处和找到示例这里. 此处.

In the class that defines hg, override getPreferredSize() to return your component's preferred size. Examples may be found here and here. The rationale and some important caveats are discussed here.

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