EmbMicro EmbMicro - 1 year ago 103
Java Question

Constant Width SashForm

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() {
public void controlResized(ControlEvent e) {
int width = sashForm.getClientArea().width;
int[] weights = sashForm.getWeights();
weights[1] = width - weights[0];

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 Source

This is the best solution I could come up with.

import org.eclipse.swt.SWT;
import org.eclipse.swt.custom.SashForm;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Listener;
import org.eclipse.swt.widgets.Shell;

public class Main {
private static int leftWidth, oldWeight;

public static void main(String[] args) {
    Display display = new Display();
    final Shell shell = new Shell(display);
    shell.setLayout(new FillLayout());
    shell.setSize(600, 400);

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

    final Button button = new Button(form, SWT.PUSH);

    button.addListener(SWT.Resize, new Listener() {
        public void handleEvent(Event arg0) {
            int[] weights = form.getWeights();
            // oldWeights is used to distinguish between a window resize and
            // a sash move
            if (oldWeight != weights[0]) {
                System.out.println("Weights changed!");
                oldWeight = weights[0];
                leftWidth = (int) Math.round((double) form.getClientArea().width
                        * (double) weights[0]
                        / (double) (weights[0] + weights[1]));

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

    form.setWeights(new int[] { 200, 800 });
    leftWidth = 200;

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

            double perChange = (double) leftWidth / (double) width;

            weights[0] = (int) (perChange * 1000.0);
            weights[1] = 1000 - weights[0];

            // oldWeights must be set before form.setWeights
            oldWeight = weights[0];

    while (!shell.isDisposed()) {
        if (!display.readAndDispatch())

The sash jumps around about 1px when the window is resized due to rounding issues, but it seems to do what I want.

This is a very hacky solution and I would like to know if there is a better one. It also crashes if you make the window smaller than the left button, but that is easy to fix.