How to layout a components in vertical only scrollpane?

Question

I have a complex question I cant find an answer anywhere.

here is a example :

public static void main(final String[] args) {
    final JFrame frame = new JFrame("test");
    final JPanel bigPane = new JPanel(new GridLayout(0, 1));
    frame.setContentPane(new JScrollPane(bigPane, ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED,
            ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER));
    bigPane.add(new JTextField("reterterter ertertrert erterter ert"));
    bigPane.add(new JTextField(" ertertrert erterter ert"));
    bigPane.add(new JTextField("reterterter ertertrert  ert"));
    bigPane.add(new JTextField("reterterter ertertrert erterter "));
    frame.pack();
    frame.setSize(frame.getSize().width/2, frame.getSize().height);
    frame.setVisible(true);
}

Here, clearly the textfields are cut. More precisely, bigPane is cut. But I would like the textfields to be resized instead of cut, so we can still use them.

Since the horizontal scrollbar is forbidden to appear, I would like the layout to forget the view's (bigPane) preferred width and always force the view's width to match the viewport's width. Like there would be no virtual viewport for the horizontal direction, only in the vertical.

I can't find a solution to that, and not even a hack, thaks if you can help.

Nico.

PS: looks like the code for ViewportLayout doesn't contain any code for that

PS2 : here is a cap of the result of the above code http://www.nraynaud.com/kilombo/testLayout.png see the right side.

Answer 1

I think the "correct" way to do this is to use the Scrollable interface:

public class ScrollPaneWidthTrackingPanel extends JPanel implements Scrollable {
    private static final long serialVersionUID = 1L;

    public ScrollPaneWidthTrackingPanel(LayoutManager layoutManager) {
        super(layoutManager);
    }

    public Dimension getPreferredScrollableViewportSize() {
        return getPreferredSize();
    }

    public int getScrollableBlockIncrement(Rectangle visibleRect, int orientation, int direction) {
        return Math.max(visibleRect.height * 9 / 10, 1);
    }

    public boolean getScrollableTracksViewportHeight() {
        return false;
    }

    public boolean getScrollableTracksViewportWidth() {
        return true;
    }

    public int getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction) {
        return Math.max(visibleRect.height / 10, 1);
    }
}

Two lines of your code then have to change to:

final ScrollPaneWidthTrackingPanel bigPane = new ScrollPaneWidthTrackingPanel(new GridLayout(0, 1));
frame.setContentPane(new JScrollPane(bigPane));

And the components should always fill the entire width of the JScrollPane, whatever the size of the frame. This change has a side effect that the components will now not fill the height of the JScrollPane. To solve that add the following code to the top of the getScrollableTracksViewportHeight method:

if (getParent() instanceof JViewport) {
    JViewport viewport = (JViewport) getParent();
    return component.getPreferredSize().height < viewport.getHeight();
}

Answer 2

Use the JTextField constructor which takes an int as a parameter. This is the number of visible characters in the text field. You can then use setText to initialize the contents of the field (if required).

Alternatively, set the maximum and preferred sizes (setMaximumSize, setMinimumSize) of the text fields appropriately.

Answer 3

From the JavaDoc:

Parameters:
text - the text to be displayed, or null
columns - the number of columns to use to calculate the preferred width; if columns is set to zero, the preferred width will be whatever naturally results from the component implementation

Since you're calling the 0 constructor, you're getting the "whatever naturally results" implementation, which takes the lengths of your too-long strings. Simply calling the columns constructor, with a non-zero will fix this for you. Try these lines:

bigPane.add(new JTextField("reterterter ertertrert erterter ert",3));
bigPane.add(new JTextField(" ertertrert erterter ert",3));
bigPane.add(new JTextField("reterterter ertertrert  ert",3));
bigPane.add(new JTextField("reterterter ertertrert erterter ",3));

Here is a screenshot of the resulting pane:

_{(source: mcglashan.net)}