java awt swing控件，下拉内容，自适应宽度

原创已于 2022-10-26 09:31:32 修改

· 1.2k 阅读

3 ·

版权

文章标签：

#java #开发语言

于 2022-10-22 13:16:04 首次发布

本文介绍如何通过继承 JCombobox 并重写 doLayout 和 getSize 方法，实现DefaultComboBox 的下拉宽度自适应，确保即使组合框本身较小，也能显示所有选项。涉及的方法包括计算内容宽度和调整布局尺寸。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

效果图
在这里插入图片描述
1.使用继成复写父类方法的方式进行下拉宽度修改DefaultComboBox 继承JComboBox

 class DefaultComboBox extends JComboBox {
  public DefaultComboBox(ComboBoxModel var2) {
            super(var2);
  }
 }

2.修改下拉画布宽度

 		 /**
         * Small hack to get pop up menu size bigger enough to show items even though
         * the combo box size could be smaller
         * */
        private boolean layingOut = false;
        @Override
        public void doLayout(){
            try{
                layingOut = true;
                super.doLayout();
            }finally{
                layingOut = false;
            }
        }
        @Override
        public Dimension getSize(){
            Dimension dim = super.getSize();
            if ( !layingOut ) {
                dim.width = Math.max(dim.width, computeMaxWith());
            }
            return dim;
        }

3.计算下拉框内容宽度，并获取最大宽度

 public Integer computeMaxWith(){
            Font font = this.getFont();
            int maxWith = 0;
            for (int i = 0; i < this.getModel().getSize(); i++) {
                Object elementAt = this.getModel().getElementAt(i);
                Integer width = getWidth(elementAt.toString(), font);
                maxWith = Math.max(maxWith,width);
            }
            return maxWith+5;
        }
        public Integer getWidth(String text,Font font){
            FontMetrics fm = Toolkit.getDefaultToolkit().getFontMetrics(font);
            int width = SwingUtilities.computeStringWidth(fm, text);
            return width;
        }

4.完整代码

 class DefaultComboBox extends JComboBox {
  public DefaultComboBox(ComboBoxModel var2) {
            super(var2);
  }
   		/**
         * Small hack to get pop up menu size bigger enough to show items even though
         * the combo box size could be smaller
         * */
        private boolean layingOut = false;
        @Override
        public void doLayout(){
            try{
                layingOut = true;
                super.doLayout();
            }finally{
                layingOut = false;
            }
        }
        @Override
        public Dimension getSize(){
            Dimension dim = super.getSize();
            if ( !layingOut ) {
                dim.width = Math.max(dim.width, computeMaxWith());
            }
            return dim;
        }
        public Integer computeMaxWith(){
            Font font = this.getFont();
            int maxWith = 0;
            for (int i = 0; i < this.getModel().getSize(); i++) {
                Object elementAt = this.getModel().getElementAt(i);
                Integer width = getWidth(elementAt.toString(), font);
                maxWith = Math.max(maxWith,width);
            }
            return maxWith+5;
        }
        public Integer getWidth(String text,Font font){
            FontMetrics fm = Toolkit.getDefaultToolkit().getFontMetrics(font);
            int width = SwingUtilities.computeStringWidth(fm, text);
            return width;
        }
 }