对SpringLayout有帮助吗？

Question

I have a very odd problem when I use Java's SpringLayout manager. I'm triyng to get a tool bar to appear in my program. It was working at an earlier point in my program and now it does not work. Basically, if I remove the layout parameter from my instantiation of a JPanel the elements that I have added in the JPanel show up, albeit without my customizations. If I have that parameter in the instantiation, the toolbar does not appear at all. I have no idea what I jacked up or am doing wrong. The JPanel is going into a central JFrame, which I've changed around from a BorderLayout to another SpringLayout to nothing and it does not seem to affect this problem.

public class purchaserApp
{
static JFrame mainWindow;                                   //Main window
static JFrame addView = new JFrame ("Add An Item...");      //Add item window
static JFrame aboutView = new JFrame ("About Purchaser");   //About window
static JFrame helpView = new JFrame ("Purchaser Help");     //Help window
static JPanel toolBar, contentArea, previewPane;            //Panels for GUI
static JRootPane root;
static JToolBar toolBar2;
//SpringLayout mainLayout;
JTable table;

public purchaserApp()
{
    makemainWindow();
    makeMenu();
    makeToolbar();
     // makeMainContentView();
    mainWindow.setVisible(true);

}
public void makeToolbar()
{
    SpringLayout tbLayout = new SpringLayout();
    toolBar = new JPanel(tbLayout);     //this is the offending line of code, if I remove "tbLayout" the buttons show up in the GUI but obviously without the customizations I made below...
    JButton toolBarButtons[];
    String buttonNames[] = {"Add", "Edit", "Delete"};
    //Instantiate buttons for toolbar
    toolBarButtons = new JButton[3];
    //Resize
    Dimension d = new Dimension (40,55);

    //Add/modify/whatever
    for (i = 0; i < 3; i++)
    {
        toolBarButtons[i] = new JButton(buttonNames[i]);
        toolBarButtons[i].setPreferredSize(d);
        tbLayout.putConstraint(SpringLayout.NORTH, toolBarButtons[i], 5, SpringLayout.NORTH, toolBar);
    }

    //Adjust constraints
    tbLayout.putConstraint(SpringLayout.WEST, toolBarButtons[0], 5, SpringLayout.WEST, toolBar);
    tbLayout.putConstraint(SpringLayout.WEST, toolBarButtons[1], 5, SpringLayout.EAST, toolBarButtons[0]);
    tbLayout.putConstraint(SpringLayout.EAST, toolBarButtons[2], -5, SpringLayout.EAST, toolBar);       //due to x-axis, we must go negative to get inside the frame
    for (i = 0; i < 3; i++)
        toolBar.add(toolBarButtons[i]);

    mainWindow.add(toolBar,BorderLayout.NORTH);   //Lies! Does not add

}

I've included here the class and the offending method. Any help would be most greatly appreciated as I'm sure I am not the first one to have this problem. I also apologize if this is a relatively simple fix and I did not see it. I'm still sorta new to Java GUIs (and Java in general) so please excuse me.

Answer 1

Why are you trying to create a toolbar using a panel? Whats wrong with JToolBar which uses its own custom layout?

Even if you did create a custom toolbar panel I wouldn't use a SpringLayout, its too complicated. Just use a FlowLayout or a horizontal BoxLayout.

Read the Swing tutorial on Layout Managers for working examples of each layout manager.

Answer 2

As noted in this related question , the order of constraint specification may be important, particularly if the resulting layout is over-constrained . Depending on the version, you may have to specify the EAST/SOUTH constraints before the WEST/NORTH constraints, as described here .