java - JScrollPane 无法与 JPanel 和 JFrame 一起使用

Question

对于我的代码，我做了类似的事情:

Jframe frame = new JFrame();
JPanel panel = new JPanel();

JButton button = new JButton();
// after locating and resizing buttons...
panel.add(button);

// and after many codes about buttons and labels...

frame.add(panel);

JScrollPane scroll = new JScrollPane(panel);
scroll.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
frame.add(scroll);

据我所知，这应该是正确的，但我无法滚动。 滚动条内的灰色条丢失。

感谢您的关注和时间! <3

image for better idea of what's happening to my code.

Answer 1

如果您阅读 https://docs.oracle.com/javase/tutorial/uiswing/components/scrollpane.html 上有关滚动 Pane 的官方教程，他们注意到这些政策:

VERTICAL_SCROLLBAR_ALWAYS

HORIZONTAL_SCROLLBAR_ALWAYS

Always display the scroll bar. The knob disappears if the viewport is large enough to show the whole client.