jscrollpane to scrolling a panel

Question

hi i have to writing an applet, in left side i must use an panel to contain a list of vehicles that can be a list of buttons,what is the problem, number of the vehicles are not given !!! so, i need to scrolling panel when number of vehicles is too much,

i do this for jframe, but it didn't work correct with panel, please help me with an example

the code i use to scrolling panel is :

 public class VehicleList extends JPanel {
    private ArrayList<VehicleReport> vehicles;
    private ArrayList<JButton> v_buttons =  new ArrayList<JButton>();



 public void showList(ArrayList<Vehicles> vehicles)
 {
   this.vehicles = vehicles;
   //...
    add(getScrollpane());
    setSize(155,300);

 }

public JScrollPane getScrollpane()
{
  JPanel panel = new JPanel();
  panel.setPreferredSize(new DimensionUIResource(150, 300));
   GridBagLayout gridbag = new GridBagLayout();
    GridBagConstraints constraint = new GridBagConstraints();
    panel.setLayout(gridbag);
    constraint.fill = GridBagConstraints.HORIZONTAL;
    JLabel title = new JLabel("Vehiles list");
    constraint.gridwidth = 2;
    constraint.gridx = 0;
    constraint.gridy = 0;
    constraint.ipady = 230;
    gridbag.setConstraints(title, constraint);
    panel.add(title);
    // end of set title
    constraint.gridwidth = 1;
    int i=1;

    for(JButton jb : v_buttons )
    {
        constraint.gridx =0;
        constraint.gridy = i;
        gridbag.setConstraints(jb, constraint);
        panel.add(jb);
        JLabel vehicle_lable = new JLabel("car" + i);
        constraint.gridx = 1;
        constraint.gridy = i;
        gridbag.setConstraints(vehicle_lable, constraint);
        panel.add(vehicle_lable);
        i++;
    }
JScrollPane jsp = new JScrollPane(panel);
 return jsp;

}

}

in jaframe after add jscrollpane to jframe i place this

pack();

setSize(250, 250);

setLocation(100, 300);

and it work clearly!!!!

Answer 1

You need to set the scrolling policy on the horizontal and vertical:

public void setHorizontalScrollBarPolicy(int policy)
public void setVerticalScrollBarPolicy(int policy)

Using:

JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED
JScrollPane.HORIZONTAL_SCROLLBAR_NEVER
JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS

And:

JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED
JScrollPane.VERTICAL_SCROLLBAR_NEVER
JScrollPane.VERTICAL_SCROLLBAR_ALWAYS

So for example:

jscrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);

Answer 2

You also don't show us the layout manager of the VehicleList JPanel. In case you aren't setting it, it defaults to FlowLayout, unlike JFrame (which you mentioned this does work in), whose content pane defaults to BorderLayout. So maybe you just need to change the relevant code from:

//...
add(getScrollpane());

to

//...
setLayout(new BorderLayout());
add(getScrollpane(), BorderLayout.CENTER);