Question

我有一个以这种方式生成的JComboBox。

private JComboBox generateComboBox() {

    JComboBox ddl = new JComboBox();
    ArrayList<String> items = null;
    if(this.editable)
        items = (ArrayList<String>) Registry.getListEditable();
    else
        items = (ArrayList<String>)  Registry.getListNotEditable;
    for(String s:items)
        ddl.addItem(s);
    return ddl;
}

此ComboBox在此处使用该代码显示在JFrame上：

        GridBagConstraints constraints = new GridBagConstraints();
        constraints.gridheight = 3;
        constraints.gridwidth = 1;
        constraints.gridx = 0;
        constraints.gridy = 0;
        this.getRootPane().add(ddl_schemes,constraints);

问题是，＆＃34;下拉＆＃34;功能不可见。 ComboBox包含值，我可以使用键盘上的箭头键选择这些值，但是我看不到列表。

有什么建议吗？

谢谢！

Answer 1

这很有效。所以你的问题可能在任何其他方面。发布更多代码或完整示例。为什么要将所有内容添加到 rootpane ？将其添加到 contentpane 。

了解更多信息：http://docs.oracle.com/javase/tutorial/uiswing/components/rootpane.html

package testing;

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.util.Arrays;
import java.util.List;
import javax.swing.JComboBox;
import javax.swing.JFrame;

public class JComboBoxMaster extends JFrame {

  private JComboBox generateComboBox() {
    JComboBox ddl = new JComboBox();
    List<String> items = Arrays.asList("one", "two", "three");

    for (String s : items) {
      ddl.addItem(s);
    }

    return ddl;
  }

  public static void main(String[] args) {
    JComboBoxMaster jcbm = new JComboBoxMaster();
    jcbm.setLayout(new GridBagLayout());
    jcbm.setDefaultCloseOperation(EXIT_ON_CLOSE);

    GridBagConstraints constraints = new GridBagConstraints();
    constraints.gridheight = 3;
    constraints.gridwidth = 1;
    constraints.gridx = 0;
    constraints.gridy = 0;
    JComboBox test = jcbm.generateComboBox();
    jcbm.getContentPane().add(test, constraints);

    jcbm.pack();
    jcbm.setVisible(true);

// This works
    test.addItem("four");

  }
}

没有显示Combobox的DropDown

1 个答案: