JScrollPane无法在null布局中工作 [英] JScrollPane not working in null layout

问题描述

  import javax.swing.JCheckBox;
  import javax.swing.JFrame;
  import javax.swing.JLabel;
  import javax.swing.JPanel;
  import javax.swing.JScrollPane;

public class ScrollJPanelDemo extends JFrame {
   public ScrollJPanelDemo(){
    setSize(480, 200);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JLabel label = new JLabel("Select one or more options : ");
    JCheckBox jcb1 = new JCheckBox("Chandigarh");
    JCheckBox jcb2 = new JCheckBox("Mohali");
    JCheckBox jcb3 = new JCheckBox("Delhi");
    JCheckBox jcb4 = new JCheckBox("Noida");
    JCheckBox jcb5 = new JCheckBox("Mumbai");
    JCheckBox jcb6 = new JCheckBox("Kolkata");

    //creating JPanel to hold the checkboxes
    JPanel jpnl = new JPanel();
    jpnl.setLayout(null);
    jpnl.setOpaque(true);
    jcb1.setBounds(0,0,100,40);
            jcb2.setBounds(0,60,100,40);
            jcb3.setBounds(0,120,100,40);
            jcb4.setBounds(0,180,100,40);
            jcb5.setBounds(0,240,100,40);
            jcb6.setBounds(0,300,100,40);
    //adding check boxes and label to the JPanel
    jpnl.add(label);
    jpnl.add(jcb1);
    jpnl.add(jcb2);
    jpnl.add(jcb3);
    jpnl.add(jcb4);
    jpnl.add(jcb5);
    jpnl.add(jcb6);

    //creating the scroll pane that will scroll the panel.
    JScrollPane jscrlPane = new JScrollPane(jpnl);
    jscrlPane.setBounds(0,0,300,300);



        jscrlPane.setHorizontalScrollBarPolicy
       (JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS) ;
   jscrlPane.setVerticalScrollBarPolicy
   (JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

    //adding that scroll pane to the frame.
    getContentPane().add(jscrlPane);
    setVisible(true);
  }

    public static void main(String args[]){
            new ScrollJPanelDemo();             
        }

 }

我是Java Swing的新手，并尝试在Java代码上使用滚动"窗格，但无法正常工作.滚动窗格是在垂直方向上添加到框架上的，但无法使用.

I'm new in Java Swing and try to use of Scroll pane on my Java code, but it's not working. The Scroll Pane is add on the frame in vertical direction but not worked.

推荐答案

您应该创建自己的面板，该面板扩展JPanel并包含所有复选框，并在该面板中覆盖getPreferredSize()方法，例如:

You should create your own panel that extends JPanel containing all checkboxes and in this panel override getPreferredSize() method like:

@Override
public Dimension getPreferredSize()
{
    return new Dimension( 300,300 );
}

并在您的代码中使用它:

and use it in your code:

...

// creating the scroll pane that will scroll the panel.
JScrollPane jscrlPane = new JScrollPane( new MyPanelWithCheckboxes() );
jscrlPane.setBounds( 0, 0, 300, 300 );
...

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