为什么JLabel在使用SpringLayout时有零高度？

Question

我是Java设计的新手，我尝试使用SpringLayout创建表单。我将JLabel放在JFrame中，添加了一些约束。我需要JLabel，以JPanel宽度为单位。但它的高度是零。宽度太小了。

下面是代码片段：

imageContainer = new JLabel();
imageContainer.setBorder(BorderFactory.createLineBorder(Color.BLACK));

filterButton = new JButton("Filter");
filterButton.addActionListener(filter);

layout.putConstraint(SpringLayout.WEST, imageContainer, 5, SpringLayout.WEST, this);
layout.putConstraint(SpringLayout.NORTH, imageContainer, 5, SpringLayout.NORTH, this);
layout.putConstraint(SpringLayout.EAST, imageContainer, 5, SpringLayout.EAST, this);

layout.putConstraint(SpringLayout.WEST, filterButton, 5, SpringLayout.WEST, this);
layout.putConstraint(SpringLayout.NORTH, filterButton, 5, SpringLayout.SOUTH, imageContainer);
layout.putConstraint(SpringLayout.SOUTH, filterButton, 5, SpringLayout.SOUTH, this);

这是结果

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我哪里出错了？如何将JLabel大小扩展到父容器？

Answer 1

我的问题不在JLablel。我试图在约束中使用这个，但实际上它是不正确的。你需要像这样的容器：

Container contentPane = this.getContentPane();

之后，您可以在约束中使用contentPane：

layout.putConstraint(SpringLayout.WEST, imageContainer, 5, SpringLayout.WEST, contentPane);
layout.putConstraint(SpringLayout.NORTH, imageContainer, 5, SpringLayout.NORTH, contentPane);
layout.putConstraint(SpringLayout.EAST, imageContainer, -5, SpringLayout.EAST, contentPane);
layout.putConstraint(SpringLayout.SOUTH, imageContainer, -5, SpringLayout.NORTH, filterButton);

layout.putConstraint(SpringLayout.WEST, filterButton, 5, SpringLayout.WEST, contentPane);
layout.putConstraint(SpringLayout.SOUTH, filterButton, -5, SpringLayout.SOUTH, contentPane);

还有这份工作。