Frame中为什么setLayout(null)时无法显示Choice????
问题同上,代码如下:只是很奇怪!!!谢谢...
import java.awt.Panel;import java.awt.Button;import java.awt.event.WindowAdapter;import java.awt.event.WindowEvent;import java.awt.Choice;import java.awt.Frame;import java.awt.event.ActionEvent;import java.awt.event.ItemEvent;import java.awt.event.ItemListener;import java.awt.event.ActionListener;public class AdvanceSetFrame extends Frame implements ActionListener, ItemListener { private Choice timeChoice; private Button btnEnter, btnCancel; private Panel panel; final String enterStr = "确定"; final String cancelStr = "取消"; final static String title = "高级设置";// 当static不标时会有提示于super(title):Cannot // refer to an instance field title // while explicitly invoking a // constructor public AdvanceSetFrame() { super(title); setBounds(500, 300, 400, 200); setLayout(null); panel = new Panel(); timeChoice = new Choice(); timeChoice.add("1.0"); timeChoice.add("1.5"); timeChoice.add("2.0"); timeChoice.add("2.5"); timeChoice.add("3.0"); timeChoice.setVisible(true); timeChoice.addItemListener(this); panel.add(timeChoice); add(panel); setVisible(true); btnEnter = new Button(enterStr); btnCancel = new Button(cancelStr); btnEnter.addActionListener(this); btnCancel.addActionListener(this); btnEnter.setBounds(145, 170, 50, 20); btnCancel.setBounds(205, 170, 50, 20); add(btnEnter); add(btnCancel); addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { setVisible(false); } }); } public void itemStateChanged(ItemEvent e) { // TODO Auto-generated method stub if (e.getItemSelectable() == timeChoice) {// if (timeChoice.getSelectedIndex() == 0) {// } else if (timeChoice.getSelectedIndex() == 1) {// } else if (timeChoice.getSelectedIndex() == 2) {// } else if (timeChoice.getSelectedIndex() == 3) {// } else if (timeChoice.getSelectedIndex() == 4) {// } } } @Override public void actionPerformed(ActionEvent e) { // TODO Auto-generated method stub if(e.getSource() == btnEnter){ this.setVisible(false); }else if(e.getSource() == btnCancel){ this.setVisible(false); } }}public class BeadrollFrame{ public static void main(String []args){ new AdvanceSetFrame(); }}