java grid bag layout: avoiding center alignment

Question

Hi,

In my GUI application, I have several JPanels that are instantiated at various points during the running of my program, and certain actions will cause one of them to be displayed in a scroll pane:

mViewport.setViewportView(currentPanel);

The trouble is, that my panels are done using Grid Bag Layouts, and the behaviour of that is to center itself within the JScrollPane it is inside of. This make the GUI look weird.

Anyone know of a way to force a grid bag layout panel to top-left align?

Thanks!

---

EDIT

Note that here I am asking about the alignment of the entire panel within its scroll pane, not about the components within the panel.

Answer 1

You will need to set the weights (in the GridBagConstraints) on one or more of the components inside your panel. This has the effect of "pushing" the components to take up more of the available space (without weights, the components will only take up what they need, and the panel will be centred within the available space).

If you wanted to align the components at the top left of the scroll pane, set the bottom component's y weight to 1.0, and set the right-most component's x weight to 1.0.

Answer 2

I found a solution to my own question after some fiddling around:

Setting weights appears to be able to affect alignment of the components within the JPanel for which the GridBagLayout was used. However, it didn't have an effect on the alignment of the JPanel within the JScrollPane.

I found a rather simple solution, which is to not put the JPanel directly inside of the JScrollPane, as I was doing with my earlier code:

if (currentPanel != mCurrentPanel)
{
    mViewport.setViewportView(currentPanel);
}

... but instead to put an "outer" JPanel inside the JScrollPane, and set that to use a FlowLayout. Then when I want to switch panels, I remove the old and place the panel within the "outer" panel.

if (currentPanel != mCurrentPanel)
{
    if (mCurrentPanel != null)
    {
        mOuterPanel.remove(mCurrentPanel);
    }
    mCurrentPanel = currentPanel;
    mOuterPanel.add(mCurrentPanel);
}

This approach worked rather well, because it meant I only had to effect changes in one class, instead of each of the many panels I had.