JComboBox弹出菜单没有出现 [英] JComboBox popup menu not appearing

问题描述

我在JPanel中有一个JComboBox（它本身嵌套在其他一些JPanel中）。它包含了一个枚举成员。我遇到了一个问题，当我点击展开按钮时没有出现弹出菜单。

I have a JComboBox inside a JPanel (which itself is nested within a few other JPanels). It's populated with members of an enum. I'm running into a problem where the popup menu doesn't appear when I click the expand button.

这是我到目前为止收集的信息：

Here's the information I've gathered so far:

1）首次点击展开按钮不会做任何事情。第二次点击会突出显示该框的内容，但弹出窗口仍然没有显示。

1) The first click on the expand button does nothing. The second click highlights the contents of the box, but the popup still doesn't appear.

2）一旦我点击了按钮并给予它焦点，就/向下击键可以正确地循环输入条目。

2) Once I've clicked the button and given it focus, up/down keystrokes cycle through the entries correctly.

3）我尝试添加PopupMenuListener来打印事件，事件以无法解释的方式触发：

3) I've tried adding a PopupMenuListener to print out events, and the events fire in unexplained ways:

mouse down: popupMenuWillBecomeVisible fires
mouse up: nothing
mouse down: popupMenuWillBecomeInvisible fires
mouse up: nothing

这是我对JComboBox的初始化代码：

Here's my initialization code for the JComboBox:

comboBox = new JComboBox();
comboBox.setPreferredSize(new Dimension(175, 30));
comboBox.setMaximumSize(new Dimension(175, 30));
comboBox.setAlignmentX(0.5f);

comboBox.addItem(Enum.Value1);
...     

parentPanel = new JPanel();
parentPanel.setLayout(new BoxLayout(parentPanel, BoxLayout.X_AXIS));
parentPanel.setMaximumSize(new Dimension(37267, 50));

... add some other stuff to parentPanel ...

parentPanel.add(comboBox);

有没有人知道为什么弹出菜单可能不会出现？

Does anyone have any idea why the popup menu might not be appearing?

感谢您的帮助！

推荐答案

我遇到了同样的问题，并想知道出了什么问题，因为通常它是有效的，而且那种bug非常非常关键。

I had the same issue and was wondering what was wrong, because usually it works and that kind of bug would be very very critical.

所以我删除了所有我只有一个带有JComboBox的JDialog的main方法的内容它。

So I deleted everything that I just had a main-method with an JDialog with just an JComboBox within it.

当我删除所有内容时，我意识到我做错了什么：我使用了 getRootPane（）而不是 getContentPane（）。

The moment I had deleted everything I realized what I've done wrong: I used getRootPane() instead of getContentPane().

我通常使用ESC关闭对话框并将KeyStroke添加到rootPane。这就是我不小心弄错的原因。

I usually use ESC for closing the dialog and add the KeyStroke to the rootPane. That was the reason for my careless mistake.

我希望这会帮助下一个犯错的人：）

I hope that will help the next ones doing that mistake : )

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