Constant Width SashForm

Question

My application has a SashForm with two children. I want the left child to stay the same size when the window is resized. I want the same thing Eclipse does with the Package Explorer and the main editor. When you resize the window only the text editor changes size. However, the Package Explorer is still resizeable by the sash.

I tried using the following

sashForm.addControlListener(new ControlAdapter() {
    @Override
    public void controlResized(ControlEvent e) {
        int width = sashForm.getClientArea().width;
        int[] weights = sashForm.getWeights();
        weights[1] = width - weights[0];
        sashForm.setWeights(weights);
    }
});

The problem is the width of the left size either shrinks to 0 or expands too much. It looks like the weights are updated before this is called or something.

If I set weights[0] equal to some constant it does what I want.

Answer 1

I managed to get an example running that should give you an idea how to solve your problem. The thing is, that the SashForm uses weights rather than pixels. So you have to compute the percentage the left child has to occupy based on the parent size and assign the rest to the right child.

In my code example, you can specify the width of the left child and set a minimal size for the right child, such that the SashForm will always show both.

private static final int MIN_WIDTH_LEFT = 100;
private static final int MIN_WIDTH_RIGHT = 50;

public static void main(String[] args)
{
    Display display = new Display();
    final Shell shell = new Shell(display);
    shell.setText("StackOverflow");
    shell.setLayout(new FillLayout());

    final SashForm form = new SashForm(shell, SWT.HORIZONTAL);

    Button button = new Button(form, SWT.PUSH);
    button.setText("Left");

    Button buttonR = new Button(form, SWT.PUSH);
    buttonR.setText("Right");

    form.setWeights(new int[] {1, 2});

    shell.addListener(SWT.Resize, new Listener()
    {
        @Override
        public void handleEvent(Event arg0)
        {
            int width = shell.getClientArea().width;
            int[] weights = form.getWeights();

            if(width >= MIN_WIDTH_LEFT + MIN_WIDTH_RIGHT)
            {
                weights[0] = 1000000 * MIN_WIDTH_LEFT / width;
                weights[1] = 1000000 - weights[0];
            }
            else
            {
                weights[0] = 1000000 * MIN_WIDTH_LEFT / (MIN_WIDTH_LEFT + MIN_WIDTH_RIGHT);
                weights[1] = 1000000 * MIN_WIDTH_RIGHT / (MIN_WIDTH_LEFT + MIN_WIDTH_RIGHT);
            }

            System.out.println(width + " " + Arrays.toString(weights));

            form.setWeights(weights);
        }
    });

    shell.pack();

    shell.setSize(600, 400);
    shell.open();
    while (!shell.isDisposed())
    {
        if (!display.readAndDispatch())
            display.sleep();
    }
    display.dispose();
}

This is what it looks like:

Startup:

After resizing:

When decreasing the window size until it is too small to show both minimal sizes:

As you can see in this case, the minimal size for the left child is ignored to still be able to show both childs.